Sealed type plasma torch

Abstract

A sealed plasma torch assembly is described. In various embodiments, the sealed plasma torch completely separates the inert gas flowing inside the torch to form the plasma from the ambient air. In this way, the inert gas (e.g., argon) is not mixed with the air. The sealed torch allows for better heat management, reduced gas consumption, and simpler and less expensive construction in various embodiments. Gas may be recirculated to further reduce gas consumption. Repeatability of analytical measurements using the plasma torch may be improved since the plasma torch pressure is independent of atmospheric pressure. Methods of using the plasma torch are also described.

Description

[Technical field]

[0001] Related Applications

[0001] This application claims priority from Provisional Patent Application No. 63 / 333,942, filed April 22, 2023, the disclosure of which is incorporated by reference in its entirety into this specification.

[0002] Technical Field

[0002] The present disclosure relates to plasma torches, and in particular to a novel sealed plasma torch for generating inductively coupled plasma (ICP) for use, for example, in mass cytometry (ICP-MS) and optical emission spectrometry (ICP-OES). [Background technology]

[0003] background

[0003] Plasma torches are employed to ionize and / or excite samples through exposure of the sample to an inductively coupled plasma. One example of an analytical inductively coupled plasma (ICP) torch is the outdoor type (including the Fassel type torch). The Fassel type torch includes three concentric quartz tubes inserted into a helical coil connected to a high voltage radio frequency (RF) generator. Argon can be introduced through the rims of the concentric quartz tubes and flows into the induction zone where a plasma can be generated and maintained by an RF electromagnetic field, and subsequently into the analytical zone where sample atom ionization (for mass spectrometry) or excitation (for optical emission spectrometry) can take place.

[0004]

[0004] Most of the argon is then dispersed into the surrounding air, and a small portion (typically about 2 sLpm) is collected for mass spectrometric analysis (if applicable). The torch is typically about 2 cm in diameter and consumes about 1-1.5 kW of power and about 10-20 sLpm of argon, most of which is used to dissipate the heat introduced into the plasma and to cool the torch walls.

[0005]

[0005] Outdoor torches have been used for spectroscopic purposes for decades. Outdoor torches have challenges related to the high consumption of argon used and the high heat load. The operation of outdoor torches can also be affected by atmospheric conditions. The embodiments described herein address these and other challenges. Summary of the Invention [Means for solving the problem]

[0006] overview

[0006] In one aspect, a plasma torch assembly is disclosed that includes an envelope surrounding a plasma zone, a collection chamber including a wall having at least one collector orifice, the at least one collector orifice providing fluid communication between the plasma zone and the collection chamber, and a seal for providing a sealed connection between the envelope and the wall of the collection chamber surrounding the at least one collector orifice.

[0007]

[0007] In various embodiments, the seal robustly connects the envelope to the wall.

[0008]

[0008] As an example, the seal may include a groove formed in a surface of the collector wall facing the plasma zone and a sealing element seated in the groove. Some examples of sealing elements may include O-rings and metal seals (e.g., copper gaskets).

[0009]

[0009] The plasma torch assembly may include an injector extending from a first inlet for receiving an injector gas to a first outlet for delivering at least a portion of the injector gas to the plasma zone. An injector gas supply may supply the injector gas to the injector. In various embodiments, the injector may have a frusto-conical profile with the injector outlet having a smaller cross-sectional area compared to the injector inlet.

[0010] In various embodiments, the plasma torch assembly includes a tubular structure disposed between the injector and the inner surface of the envelope and at least partially surrounding the injector to define a second inlet for delivering auxiliary gas to a region between the outer surface of the injector and the inner surface of the tubular structure, the tubular structure further defining a third inlet for delivering vortex gas to a region between the outer surface of the tubular structure and the inner surface of the envelope. The plasma torch assembly may include an auxiliary gas supplier and a vortex gas supplier for supplying the auxiliary gas and vortex gas to the torch assembly.

[0011] In various embodiments, the injector gas, the auxiliary gas, and the swirl gas can be the same gas (e.g., supplied via a single gas supply). In other embodiments, at least two of the injector gas, the auxiliary gas, and the swirl gas can be different gases. A gas manifold can be configured to receive gas from a single gas supply and to distribute a portion of the received gas as the injector gas, the auxiliary gas, and the swirl gas.

[0012] In various embodiments, the plasma torch assembly can include at least one RF coil disposed at least partially around the envelope. The RF coil is configured to regulate the pressure inside the torch envelope to approximately 4×10 4 Pa (for example, from about 13 Pa to about 4 × 10 4 The RF voltage may be configured to allow a plasma to be ignited in response to application of an RF voltage thereto (in the range of 100 .ANG. Pa).

[0013]

[0013] In various embodiments, the at least one RF coil may include two or more RF coils electrically connected in parallel. In various embodiments, the at least one RF coil has a split coil structure having two or more segments mechanically coupled to each other to surround the torch envelope and electrically coupled to provide a conductive path between the two or more segments. In various embodiments, each of the coil segments may have an approximately semicircular profile. In some such cases, the two segments may be mechanically coupled to fully surround the torch envelope.

[0014] In various embodiments, the at least one RF coil can be axially separated from the extractor orifice by a distance of about ⅓ or less of the coil diameter.

[0015] In various embodiments, the plasma torch assembly may include a radio frequency (RF) source in electrical communication with an RF coil for generating an RF electromagnetic field within at least a portion of the plasma zone to ignite a plasma. The RF source may be configured to apply an RF voltage to the RF coil at a frequency within a range of about 900 kHz to about 10 GHz. By way of example, the RF voltage may have an amplitude within a range of about 50 V to about 6 kV.

[0016]

[0016] The plasma torch assembly further includes at least one exhaust channel formed in the wall and extending from an inlet opening to an outlet opening, where the inlet opening is in fluid communication with the plasma zone. At least one exhaust valve is operably coupled to the outlet opening of the at least one exhaust channel for controlling exhaust flow exiting the exhaust channel. At least one regulator can be coupled to the at least one exhaust valve for adjusting a flow rate of the exhaust exiting the exhaust channel. The regulator can be configured to adjust the exhaust flow rate to optimize the flow of plasma from the plasma zone into the collector orifice.

[0017]

[0017] As an example, in various embodiments, the wall of the collection chamber may support two or more exhaust channels. Two or more regulators operably coupled to the outlets of the exhaust channels may control the flow of gas through the exhaust channels. The regulators may be configured to establish a differential flow rate in the exhaust channels to adjust the position of the plasma relative to the orifice of the collector. For example, the wall of the collector may support two exhaust channels disposed on either side of the collector orifice. The flow rate of the exhaust gas through the channels may be adjusted to move the plasma along a first dimension (e.g., along a dimension perpendicular to the longitudinal axis of the torch assembly (e.g., the X dimension)). In some cases, two other channels may be provided in the wall to move the plasma along a second dimension. As an example, the second dimension may be perpendicular to the first dimension. In various embodiments, three or more exhaust channels may be employed to adjust the position of the plasma via adjusting the flow rate of the exhaust gas through the exhaust channels.

[0018]

[0018] A controller in communication with the regulator may send a control signal to the regulator to adjust the flow rate of exhaust gas through each exhaust channel (e.g., to optimize the flow (into the collector orifice) of ionic species and / or excited species generated within the plasma).

[0019]

[0019] In various embodiments, the first and second exhaust channels can be positioned symmetrically relative to the collector orifice, and the controller can control the regulator to provide approximately equal exhaust flow rates through the first and second exhaust channels (e.g., to center the plasma relative to the collector orifice).

[0020]

[0020] In various embodiments, the torch assembly may include at least one recirculation path fluidly coupled to at least one exhaust channel for returning at least a portion of the gas delivered to the plasma zone back to the plasma zone. In some such embodiments, a filter may be coupled to the recirculation path for filtering gas effluent flowing from the plasma zone into the recirculation path prior to returning at least a portion of the gas to the plasma zone. Any suitable filter may be utilized. By way of example and without limitation, the filter may be any of an activated carbon filter and a molecular sieve filter, among others.

[0021]

[0021] In various embodiments, the collector wall supports at least one cooling channel configured to receive a coolant. The cooling channel may be fluidly isolated from the plasma zone, i.e., no fluid path connects the cooling channel to the plasma zone. A coolant supplier in fluid communication with the at least one cooling channel may supply the coolant to the cooling channel.

[0022] In various embodiments, the injector has a length within a range of about 5 mm to about 50 mm. Further, in various embodiments, the torch envelope can have an inner diameter within a range of about 5 mm to about 30 mm.

[0023]

[0023] The torch envelope can have a wide variety of profiles (shapes). As an example, the envelope can have a generally cylindrical shape. In various embodiments, the torch envelope can have varying cross-sectional dimensions in a plane perpendicular to its longitudinal axis. As an example, the torch envelope can be in the form of a truncated cone.

[0024] The torch envelope may be formed of an electrically non-conductive material having a melting point of at least about 300° C. By way of example, and not limitation, the torch envelope may be formed of any of the following: ceramic (e.g., aluminum nitride, aluminum oxynitride, alumina, silicon nitride, sialon), glass, fused silica, and sapphire.

[0025] In various embodiments, the axial distance between the injector exit and the collector orifice can be up to about two inside diameters of the torch envelope (eg, in the range of about 5 mm to about 60 mm).

[0026] In various embodiments, the injector may be movable relative to the sampler orifice (e.g., in a plane perpendicular to the longitudinal axis of the torch assembly). For example, the injector may be mounted on a movable platform. Further, in various embodiments, the injector may be movable along the longitudinal axis of the torch assembly to change the axial distance between the injector outlet and the sampler orifice.

[0027]

[0027] The torch assembly may be enclosed within a housing. The housing may be formed of a metal, such as aluminum, copper, stainless steel, or metal-plated plastic or metal-plated ceramic. The wall thickness of the housing may be selected to protect the torch assembly from electromagnetic interference (EMI). Additionally, the housing may include one or more cooling channels for receiving a coolant.

[0028] In various embodiments, the torch assembly is approximately 1×10 5 For example, the operating pressure may be about 2×10 5 Pa ~ approx. 1×10 6 The pressure may be in the range of Pa.

[0029] In a related aspect, a plasma torch assembly is disclosed that includes an envelope surrounding a plasma zone where plasma is formed, a collection chamber including a wall having at least one collector orifice, the at least one collector orifice providing fluid communication between the plasma zone and the collection chamber, a seal for providing a hermetic connection between the envelope and the wall of the collection chamber around the at least one collector orifice, an injector disposed at least partially within the envelope, the injector extending from an inlet for receiving an injector gas flow to an outlet through which the injector gas exits the injector, and a vortex generator in fluid communication with the plasma zone, the vortex generator configured to deliver the vortex gas flow into the interior of the envelope. The axial distance between the injector outlet and the collector orifice can be in the range of about 5 mm to about 60 mm, for example in the range of about 10 mm to about 50 mm, or in the range of about 20 mm to about 40 mm. In various embodiments, the exterior surface of the injector and the interior surface of the envelope may be in direct fluid communication with one another, i.e., no structure is disposed between the exterior surface of the injector and the interior surface of the envelope.

[0030]

[0030] The envelope may have a profile configured to facilitate containment of the plasma generated within the plasma zone via the vortex gas. As an example, the envelope may have a tapered profile with a tapered cross-sectional dimension according to the tapered distance from the wall. As an example, the tapered profile of the collector may be a frusto-conical profile.

[0031]

[0031] In various embodiments, the injector may have a tapered profile with the injector outlet having a smaller cross-sectional area than the inlet of the injector.

[0032] At least one RF coil may be disposed at least partially around the envelope. An RF power source may be in electrical communication with the RF coil for supplying an RF voltage thereto. By way of example, the RF power source may be configured to apply an RF voltage to the RF coil at a frequency in a range of about 900 kHz to about 10 GHz (e.g., in a range of about 1 MHz to about 1 GHz).

[0033] In a related aspect, a method is disclosed for generating an inductively coupled plasma in a plasma torch having a torch envelope sealingly coupled to a wall of a collector of an analyzer, the method including introducing an inert gas into the interior of the torch envelope, maintaining a pressure within the torch envelope at about 4×10 4 The method includes maintaining the pressure in the torch at less than 1 Pa and establishing a radio frequency (RF) electromagnetic field within at least a portion of the interior of the torch envelope to ignite a plasma in the gas.

[0034] Following ignition of the plasma, the pressure within the torch envelope increases to, for example, 4×10 4 Pressures above 1×10 Pa (e.g., about 1×10 5 Pa ~ approx. 1×10 6 The pressure can be increased to within the range of Pa.

[0035]

[0035] An injector may be utilized to introduce the collector into the plasma zone via a carrier gas. Additionally, the position of the plasma relative to the longitudinal axis of the torch assembly may be adjusted by adjusting the injector's tilt and / or its XY position relative to the longitudinal axis, or both.

[0036]

[0036] In various embodiments, the position of the plasma relative to the longitudinal axis of the plasma torch can be adjusted by adjusting the flow rate of exhaust gas passing from the plasma zone or one or more exhaust channels provided in the wall of the collector.

[0037] In various embodiments, at least a portion of the gas introduced into the interior of the torch envelope may be removed as exhaust gas. The exhaust gas may be cooled, for example, to a temperature less than about 100° C. while passing through one or more exhaust channels formed in the wall of the collector. In some cases, at least a portion of the exhaust gas is recirculated back to the plasma zone via a recirculation path. In various embodiments, the exhaust gas is filtered prior to its recirculation to the plasma zone.

[0038]

[0038] A further understanding of the various aspects of some embodiments may be obtained by reference to the following detailed description in conjunction with the associated drawings, which are briefly described below.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings are not necessarily to scale or comprehensive. Instead, emphasis is generally placed on illustrating the principles of the embodiments described herein. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments in accordance with the present disclosure. Together with this specification, the accompanying drawings serve to explain the principles of the present disclosure. [Brief description of the drawings]

[0040] [Figure 1A]

[0041] 1 illustrates an example of a plasma torch assembly according to an embodiment of the present invention. [Figure 1B]

[0042] A cross section across the image of the wall of the collection chamber (the wall discussed above in connection with FIG. 1A) is shown. [Figure 1C]

[0043] FIG. 1 is a partial schematic diagram of three RF coils electrically connected in parallel and having a split coil configuration; [Figure 1D]

[0044] FIG. 2 is a schematic diagram of both components of each of the RF coils, where the components are mechanically coupled such that each of the RF coils surrounds the torch envelope. [Diagram 2]

[0045] 1 illustrates an example of a plasma torch assembly that provides recirculation of gases introduced into the torch assembly back to the plasma zone in accordance with some embodiments of the present invention. [Figure 3A]

[0046] FIG. 1 shows a schematic axial view of a collector orifice and the inlet openings of two exhaust channels positioned symmetrically on either side of the collector orifice along the X direction, where the gas flow rate through the exhaust channels can be adjusted to move the plasma along the X direction. [Figure 3B]

[0047] FIG. 1 shows a schematic axial view of a collector orifice and four inlet channels associated with four exhaust channels, where two of the inlet openings are symmetrically positioned on either side of the collector orifice along the X direction, and two of the inlet openings are symmetrically positioned on either side of the collector orifice along the Y direction, such that adjusting the gas flow rate through a pair positioned along the X direction allows for adjusting the position of the plasma along the X direction, and adjusting the gas flow rate in the two exhaust channels positioned along the Y direction allows for independent adjustment of the plasma position in the Y direction. [Figure 4A]

[0048] 13 illustrates positioning of plasma by adjusting exhaust flow rate through multiple exhaust channels distributed around a collector orifice to adjust the position of the plasma relative to the collector orifice according to some embodiments of the present invention. [Figure 4B]

[0048] Figure 1 illustrates positioning of the plasma by adjusting the exhaust flow rate through multiple exhaust channels distributed around a collector orifice to adjust the position of the plasma relative to the collector orifice according to some embodiments of the present invention. [Figure 4C]

[0049] 2 illustrates a schematic depiction of a moveable platform on which the injector is mounted; [Figure 4D]

[0050] 1 illustrates a schematic depiction of an example of a housing in which a torch assembly according to various embodiments may be housed, the housing sharing radio frequency power circuitry; [Figure 5A]

[0051] 1 is a schematic cross-sectional view of an example torch assembly according to an embodiment in which an auxiliary gas flow is not utilized. [Figure 5B]

[0051] FIG. 1 is a schematic cross-sectional view of an example torch assembly according to an embodiment in which an auxiliary gas flow is not utilized. [Figure 5C]

[0051] FIG. 1 is a schematic cross-sectional view of an example torch assembly according to an embodiment in which an auxiliary gas flow is not utilized. [Figure 6A]

[0052] 1 illustrates an example of a sealed plasma torch assembly according to some embodiments of the present invention. [Figure 6B]

[0052] An example of a sealed plasma torch assembly according to some embodiments of the present invention is shown. [Figure 7]

[0053] 1 illustrates an example process flow chart associated with an example method of analysis using a sealed plasma torch according to some embodiments of the present invention. [Figure 8]

[0054] 1 illustrates an example of some portions of a sealed plasma torch assembly according to some embodiments of the present invention. [Figure 9]

[0055] FIG. 1 shows a schematic diagram of a sealed torch assembly according to some embodiments of the present invention. [Figure 10]

[0056] FIG. 1 shows a schematic diagram of a sealed torch assembly according to some embodiments of the present invention. [Figure 11]

[0057] FIG. 1 shows a schematic diagram of a sealed torch assembly according to some embodiments of the present invention. [Figure 12]

[0058] FIG. 1 shows a schematic diagram of a sealed torch assembly according to some embodiments of the present invention. [Figure 13]

[0059] FIG. 1 shows a schematic diagram of a sealed torch assembly according to some embodiments of the present invention. [Figure 14]

[0060] FIG. 1 shows a schematic diagram of a sealed torch assembly according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Detailed Description

[0061] It will be appreciated that, for clarity, the following discussion will detail various aspects of embodiments of the applicant's teachings while omitting some specific details wherever convenient or appropriate to do so. For example, the discussion of similar or analogous features in alternative embodiments may be somewhat simplified. Well-known ideas or concepts may also not be discussed in detail for the sake of brevity. Those skilled in the art will appreciate that various embodiments of the applicant's teachings described herein may not require some of the specifically described details in every implementation, merely to provide a thorough understanding of some embodiments. Similarly, it will be apparent that the described embodiments may be susceptible to changes or modifications made by general knowledge without departing from the scope of the present disclosure. The following detailed description of the embodiments should not be considered in any way to limit the scope of the applicant's teachings.

[0042]

[0062] The following detailed description refers to the accompanying drawings. The same or similar reference numbers may be used in the accompanying drawings or herein to refer to the same or similar parts. Also, similarly named elements may perform similar functions and may be similarly designed unless otherwise specified. Details are described to provide an understanding of the example embodiments. Some embodiments (e.g., alternative embodiments) may be practiced without some of these details. In other instances, well-known techniques, procedures, and components have not been described in detail to avoid obscuring the described embodiments.

[0043]

[0063] Various terms are used herein according to their ordinary meaning in the art. As used herein, the term "seal" refers to a device and / or material used to bond two structures together. The term "sealed connection" refers to a connection made between two structures by using a seal, where the leakage (if any) through the connection is less than about 0.1 sLpm, or less than about 0.05 sLpm, or less than about 0.01 sLpm. The terms "plasma gas flow" and "vortex gas flow" are used interchangeably herein to refer to gases introduced into the envelope of the plasma torch through an inlet other than the inlet of the injector utilized to introduce the gas and sample into the plasma torch. "Vortex gas flow" may or may not include any vortexes as it flows through the plasma torch. As used herein, the term "rigid sealed connection" refers to a sealed connection that cannot be moved without breaking the seal. As used herein, the term "axial distance" refers to the distance between two parts / elements of the torch assembly along its longitudinal axis. "Axial distance between coil and collector orifice" refers to the minimum axial distance between the windings of the coil and the collector orifice.

[0044]

[0064] In an outdoor inductively coupled plasma (ICP) torch, an inert gas (e.g., argon) is introduced into the torch (e.g., through a quartz or ceramic tube). The gas then flows into the induction zone where a plasma is excited by a load coil connected to a radio frequency power source. The gas then exits the torch and is largely dissipated into the ambient air. Outdoor torches do not shield the plasma gas from the ambient air. Thus, heat introduced into the plasma gas in the induction zone is mostly dissipated into the ambient air. The plasma gas may also heat a collector through which ions or excited species produced in the plasma zone are introduced into a downstream analyzer (e.g., a mass spectrometer).

[0045]

[0065] In outdoor torches, mixing of the exhaust argon with ambient air can cause several problems. First, air can diffuse into the analysis zone (i.e., the area in front of the sampler orifice) and increase the amount of gas contaminants such as oxides in the analysis flow. Second, before ignition of the plasma, air also moves into the torch. This can create difficulties in ignition. Often, several sparks must be applied to ignite the plasma. Third, mixing of the hot plasma gases with air can result in the excitation or ionization of N2, O2, NO X and / or cause the formation of harmful molecules such as O3. Both the oxides and the air pollutants may be visible in mass spectrometry or other analytical techniques. To remove the harmful molecules, a closed conduit exhaust system may be used with a relatively large air flow of about 2000-4000 sLpm. An exhaust system with such requirements may be expensive to install and maintain.

[0046]

[0066] Additional problems associated with outdoor ICP torches include the high heat load imposed on the system by the plasma. Water cooling (or other liquid cooling) of outdoor ICP torches can pose some challenges. Analytical results of water-cooled torches may be less accurate. Water cooling can result in overcooling of the ICP torch. Furthermore, complex structures may be required for water cooling. Furthermore, water cooling carries the risk of water leaking into the high voltage zone. Additionally, power can leak into the water if the water becomes contaminated. This may be because the cooling water becomes contaminated over time.

[0047]

[0067] An open-air torch may allow adjustment between the center of the analysis zone and the inlet opening of the collector. An air gap between the torch and the ion collector of the analyzer may facilitate free movement of the torch assembly, thus moving the center of the analysis zone relative to the stationary position of the collector orifice. However, the implementation of such an XY adjustment mechanism may be complicated. These issues are further complicated by the need to maintain RF EMI (electromagnetic interference) shielding between the torch housing and the collector.

[0048]

[0068] Additionally, the Fassel type and many other torch types consume large amounts of argon gas (or any other gas used to generate the plasma). Mass spectrometry setups incorporating outdoor torches may also use gate valves within the vacuum boundary, which complicates the ion optics during transition to the plasma mass spectrometry analyzer. Although the vacuum system of an analyzer employing an outdoor plasma torch can handle the gas flow throughput when the plasma is on (e.g., because the high temperature of the plasma reduces the density of the flowing gas species), when the plasma is off, the air flow through the collector orifice may exceed the pumping throughput of the vacuum system.

[0049]

[0069] In contrast, in a sealed torch according to various embodiments of the present teachings, when there is no plasma, the pressure in the plasma zone can drop, thus limiting the amount of gas flowing into the vacuum system. In various embodiments, the sealed torch arrangement not only simplifies the vacuum system and offers additional flexibility in the ion optics, but also simplifies the software and firmware-based processing of the vacuum gate valve and interlocks that can transition the gate valve to a closed state when the plasma is off.

[0050]

[0070] If the plasma is not ignited, air may migrate into the flow of the inert gas used to generate the plasma. Igniting a plasma in an inert gas-air mixture may be more difficult than igniting a plasma in a pure inert gas such as argon. The plasma in an outdoor torch may be ignited by a dedicated electrode that is not used after the plasma is ignited. This ignition mechanism may use electronics to control the electrode, increasing the complexity and cost of the system.

[0051]

[0071] The ignition electrode and the mechanical XY adjustment structure limit the possible miniaturization of the torch size (especially its length). The mixing of the plasma with the ambient air means that the ICP pressure will depend on the atmospheric pressure. In addition, high mechanical vibrations can be caused by cooling fans used to cool a system heated by the plasma.

[0052] I. Sealed torch

[0072] Some embodiments described herein include a sealed ICP torch that separates and insulates the inert gas flowing inside the torch from the surrounding air and forms the plasma. For example, in various embodiments, a seal is employed to establish a hermetic connection between the torch and a wall of a collector that is utilized to introduce ions and / or excited species generated within the plasma zone of the torch into an analyzer.

[0053]

[0073] As an example, in various embodiments of a sealed torch, an outer quartz torch envelope extends to the collector and the junction between the distal end of the envelope and the wall of the collector is sealed, thus preventing the inert gas (e.g., argon) from mixing with the air.

[0054]

[0074] Since the inert gas and heat introduced into the plasma is no longer dissipated to the atmosphere, in various embodiments, the sealed torch can be complemented by a specialized liquid-cooled collector that includes channels for removing the inert gas from the torch and the plasma heat that is either carried by the plasma gases or transferred to the collector surface as heat. In various embodiments, the cooling liquid can include water and / or glycol, by way of example. Other heat removal mechanisms, such as heat pipes, heat diffusers, and evaporative coolers, can also be used to transfer heat away from the plasma region.

[0055]

[0075] In various embodiments, a sealed plasma torch may provide many advantages. Dissipation of a significant amount of plasma heat by the collector may be advantageous as it may reduce the heat load on other elements of the system. Dissipation of a significant amount of plasma heat by the collector may also facilitate treatment of the exhaust gas. Isolation of the plasma from the surrounding air may reduce the formation of oxides and therefore their detection in the mass spectrum of ions generated through the passage of the plasma. Furthermore, in various embodiments, a sealed plasma torch according to the present teachings may provide better control of gas contaminants in the mass spectrum, such as xenon, lead, and mercury, which are commonly associated with impurities in air.

[0056]

[0076] In various embodiments, the seal that provides the sealed connection between the plasma torch and the collector may be implemented as a moveable seal that would allow for adjustment of the position of the torch axis relative to the orifice of the collector, but in many embodiments the seal provides a robust sealed connection between the torch and the collector (which may eliminate the technical challenges associated with moveable seal implementations) that does not allow movement of the torch envelope relative to the collector (e.g., to align the torch axis with the orifice of the collector).

[0057]

[0077] To address the alignment of the plasma torch with respect to the collector orifice, various embodiments may employ alternative systems and methods for spatially positioning (e.g., in the XY plane perpendicular to the longitudinal axis of the plasma torch) and / or adjusting the plasma (e.g., to optimize the transfer of ions or excited species generated within the plasma to the collector orifice).

[0058]

[0078] In one such method, the part is made to tolerances and precision such that no further XY adjustments are required. In various embodiments, adjustments of the plasma (e.g., adjustments of the plasma along a direction in the XY plane) can be made by adjusting the position (e.g., XY position) or tilt angle of the injectors utilized to introduce the gas and sample into the plasma torch.

[0059]

[0079] In various embodiments, XY adjustment of the plasma can be achieved through exhaust gas flow control rather than mechanical adjustment. For example, the conductivity of the various gas output lines can be adjusted. This gas flow control adjustment is inherent to the sealed torch configuration. As an example, the flow rate of the exhaust gas through two exhaust channels symmetrically located on either side of the collector orifice can be adjusted to move the plasma in the XY plane, as discussed in more detail below.

[0060]

[0080] In various embodiments, the exhaust flow rate associated with a sealed plasma torch according to the present teachings can be as low as about 10-20 sLpm (e.g., of wasted argon) as compared to an open-air torch where the argon gas flow is mixed with a cooling air flow that typically reaches a flow of 2,000-4,000 sLpm (60-120 scfm). Furthermore, in various embodiments, the argon gas is cooled as it passes through the exhaust channel (e.g., via conduction cooling provided by one or more cooling channels formed in the collector wall). The low exhaust flow, along with the cooling of the exhaust gas, provides new opportunities for processing the exhaust flow.

[0061]

[0081] In various embodiments, at least a portion of the argon (or any inert gas used in the plasma) exhausted through the exhaust flow channel in the collector can be reintroduced into the plasma, in many cases reducing the total argon consumption to only the amount (usually about 2 sLpm) that is sampled through the collector orifice and into an analyzer (e.g., a mass spectrometer). Additionally, in various embodiments, at least a portion of the gas passing through the collector orifice can be captured and recycled back to the plasma zone. In various embodiments, nearly all of the gas flow (e.g., at least about 90%, or at least about 95%, or at least about 99%), including both the exhaust and collector flows, can be captured, filtered, and recycled, allowing the torch envelope to operate for days or even weeks without the need for a significant gas supply.

[0062]

[0082] Various embodiments of the sealed plasma torch according to the present teachings may not require a gate valve in the vacuum chamber, simplifying the vacuum system and reducing instrumentation costs and complexity. In such embodiments, elimination of the gate valve is possible because the flow of gas in the sealed torch can be controlled. For example, when the plasma is off, an orifice in the collector can direct a large amount of gas through the collector orifice into the vacuum. Without a sealed connection between the plasma torch and the collector, such flow could overwhelm the vacuum pumping system, necessitating the use of a gate valve. However, with the sealed torch according to various embodiments, the amount of gas flowing into the torch can be controlled by a mass flow controller. Thus, the amount of gas that would overload the vacuum system can also be controlled and kept within the capacity of the pumping system.

[0063]

[0083] In various embodiments, a sealed plasma torch according to the present teachings does not include conventional ignition electrodes and their electronics because the plasma within the sealed torch can be self-ignited solely by an RF electromagnetic field at low pressure. In particular, the RF electromagnetic field generated by one or more RF coils surrounding the envelope can be applied at low pressures (e.g., from about 0.1 Torr (about 1.3 Pa) to about 300 Torr (about 4×10 4 Not only can it generate an RF electromagnetic field capable of causing ignition of a plasma at pressures in the range of 1000 MPa (1000 psi) but also sustain the plasma when the pressure in the plasma zone is increased, for example to above atmospheric pressure, following ignition of the plasma. This in turn allows the use of shorter plasma vessels (torches) and allows the injector length to be reduced. The reduced injector length in turn allows faster transport of the ablation plume along the path through which it travels (including through the injector conduit) from the laser ablation spot to the plasma, leading to transition times approaching 100 μs and enabling pixel speeds of 10 kHz. In combination with compact RF generators (including those built on solid components), extremely short injectors are possible. This results in a faster arrival of the laser ablation plume in the plasma and a consequent narrower spread of the resulting plume transient.

[0064]

[0084] Because the torch assembly is shielded from the atmosphere, the ICP pressure is independent of the atmospheric pressure at a given location, which enhances the repeatability of the measurement results (e.g., weather changes no longer affect the ion signal) and makes the measurement independent of the altitude of the instrument location.

[0065]

[0085] Furthermore, in various embodiments, there is a significant reduction in thermal exhaust because almost all of the plasma heat is transferred to the collector, and therefore the heat load on the benchtop system can be more easily managed. In various embodiments in which the collector includes cooling channels through which coolant flows, the heat from the plasma is primarily dissipated by the coolant flow. This coolant flow can be managed by a cooler or a chiller that is independent of the benchtop system. Thus, residual heat in the benchtop system is minimized. This in turn eases the thermal requirements for the instrument design. For example, the enhanced heat dissipation provided by the sealed plasma torch assembly according to various embodiments can reduce the number of mechanical fans in the system, thus reducing vibration, providing an advantage of the integrated laser ablation / mass cytometry system used for imaging applications.

[0066]

[0086] Additionally, the sealed torch assembly according to various embodiments may stabilize the time required for the sample to arrive at the plasma (e.g., from the ablation cell). The flow rate through the transfer tube of the plasma torch (usually specified to be a constant flow (sLpm)) may depend on the discharge pressure. Thus, in an open-air torch, the transition rate of the ablated material through the injector depends on the ambient atmospheric pressure conditions, whereas in a sealed torch, the transition rate does not depend on the ambient atmospheric pressure conditions since the sealed torch is insulated from the surrounding environment. Thus, in various embodiments, the sealed torch may provide enhanced stability in imaging applications, since the stability of the arrival time of the sample (e.g., ablated material) may directly impact the fidelity of the imaging data.

[0067] Exemplary Torch Assembly

[0087] 1A shows a schematic diagram of an example of a plasma torch assembly 100 according to one embodiment including a torch envelope 104 that provides a housing for housing various components of the torch assembly as discussed below. As an example, the torch envelope 104 can be in the form of a tubular structure having a wide variety of profiles. In some embodiments, the torch envelope 104 can be in the form of a cylindrical tube, a truncated cone, a trumpet-like shape, or any other suitable shape (including a shape formed by rotating a profile, a parabola, about an axis of symmetry).

[0068]

[0088] As will be discussed in more detail below, the plasma torch assembly 100 further includes a collection envelope 112 having a wall 116, where the wall 116 includes a surface 120 that is in sealing contact with the torch envelope 104.

[0069]

[0089] Additionally, the torch envelope 104 may have a wide variety of inner diameters. In various embodiments (e.g., the torch envelope is a cylindrical tube), the inner diameter of the torch envelope may be approximately uniform along its length, while in other embodiments, the inner diameter of the envelope may vary along its length (e.g., in the case where the envelope is in the form of a truncated cone). The variation in inner diameter may be determined by a linear or non-linear formula (e.g., x 1 or x 2 , where x is the distance along the longitudinal axis of the torch assembly.

[0070]

[0090] The torch envelope 104 may be formed of any suitable electrically non-conductive material capable of withstanding the temperatures encountered during operation of the plasma torch assembly. Some examples of suitable materials include, for example, glass (e.g., quartz) or ceramic (such as aluminum nitride) or other suitable materials.

[0071]

[0091] In various embodiments, the torch envelope 104 can have a diameter in the range of about 0.5 to about 1 cm, or about 1 to about 3 cm, or about 3 to about 5 cm, or about 5 to about 10 cm, or greater than about 10 cm (e.g., in the range of about 10 cm to about 30 cm). As another example, the torch envelope 104 can have a length in the range of 1 to 3 cm, 3 to 5 cm, 5 to 10 cm, 10 to 20 cm, 20 to 30 cm, 30 to 50 cm, or greater than 50 cm.

[0072]

[0092] In this embodiment, the plasma torch assembly 100 may include a coil 108 (also referred to herein as an RF coil) disposed about the torch envelope 104. A power supply 125 for generating RF power is in electrical communication with the coil 108 for providing power to the coil to generate an RF electromagnetic field within a plasma zone of the torch assembly to facilitate generating and maintaining a plasma during operation of the plasma torch assembly.

[0073]

[0093] Conventionally, it is believed that the RF coil utilized in a plasma torch assembly should be positioned at a sufficient distance relative to the collector envelope to allow the magnetic flux lines generated by the coil to form a closed loop. However, as disclosed herein, it has been discovered that in various embodiments of a sealed torch assembly according to the present teachings, the RF coil can be positioned relative to the collector envelope such that the axial distance (D) between the RF coil and the collector orifice (see FIG. 2) is about 1 / 3 or less of the diameter of the RF coil. As an example, the axial distance between the RF coil and the collector orifice can be in the range of about 1 mm to about 20 mm. The ability to place the RF coil close to the collector orifice can allow for a more compact construction of the torch assembly.

[0074]

[0094] By way of example, the power supply may be configured to deliver a voltage to the coil at a frequency (such as 27.12 MHz and 40 MHz) in the range of about 1 MHz to about 10 GHz (e.g., in the range of about 1 MHz to about 300 MHz). The amplitude of the voltage may be, for example, in the range of about 50 V to about 6 kV (e.g., in the range of about 300 V to about 6 kV). In various embodiments, the coil 108 may be a single coil that is spirally wound around the torch envelope, while in some other embodiments multiple coils electrically connected in parallel may be used. Additionally, in various embodiments, the coil 108 may have a split coil configuration having two or more segments mechanically coupled to each other to surround the torch envelope and electrically coupled to provide an electrical path between the two segments. The coil 108 may be any load coil described herein or any known load coil.

[0075]

[0095] In various embodiments, multiple RF coils electrically connected in parallel may be employed. As an example, Figure 1C illustrates diagrammatically three coils 190, 192, and 194 electrically connected in parallel. One advantage of using multiple coils connected in parallel is that lower voltages can be utilized to generate the required RF electromagnetic field.

[0076]

[0096] 1C and 1D, in this embodiment, coils 192, 194, and 196 each have a split coil structure including two parts / segments (e.g., 190a and 190b) that can be mechanically connected to surround the torch envelope. Additionally, the two parts of each coil are electrically connected to allow the passage of electrical current therebetween. Although in this embodiment, the coils are each formed of two parts, in other embodiments, one or more coils utilized as RF coils may have a split coil structure including three or more parts.

[0077]

[0097] Referring again to FIG. 1A, the wall 116 may be made of a thermally conductive material such as copper. In this embodiment, the surface 120 forms a sealed connection with the torch envelope 104. For example, an O-ring 122b seated in a groove 122a formed in the surface 120 provides a seal 122 for establishing a sealed connection between the plasma torch and the wall 116. Other types of seals, such as metal seals (e.g., copper or aluminum gaskets, welded or brazed seals, or glued seals), may also be employed. Indeed, any suitable seal that can provide the desired sealed connection between the torch envelope and the extractor wall may be utilized. As discussed in more detail below, a sealed connection between the torch envelope and the extractor wall may provide several advantages.

[0078]

[0098] The surface and a portion of the torch envelope may define a plasma zone 124 (also referred to herein as an inductive zone) in which an inductively coupled plasma may be generated. Although the shape of plasma zone 124 is shown approximately in the figure, the shape is shown for illustrative purposes only and thus plasma zone 124 may take other shapes.

[0079]

[0099] In various embodiments, the surface 120 may define one or more openings that may provide fluid communication between the plasma zone and one or more channels (e.g., exhaust channels) formed in the wall 116. The number of openings provided in the surface 120 may range from 2 to 5, 5 to 10, 10 to 15, 15 to 20, or more than 20, for example. In various embodiments, the multiple openings may be uniformly distributed within the space enclosed by the torch envelope 104. As an example, the multiple openings may be distributed in a radially symmetric pattern. In various embodiments, the surface 120 may define a single opening that may accommodate all of the flow from the plasma.

[0080]

[0100] In this embodiment, a first opening 128 (also referred to herein as a collector orifice) of the plurality of openings may fluidly connect a collection chamber 132 defined by the collection envelope 112 to the plasma zone 124. The first opening 128 is disposed on a longitudinal axis 134 extending along the center of the torch envelope 104. The first opening 128 may be in the center of the wall 116 enclosed by the torch envelope 104. The first opening 128 may be considered a collector orifice or collector through which analytes ionized or excited in the plasma zone may be transferred downstream to an analyzer, such as a mass spectrometer or optical emission spectrometer.

[0081]

[0101] The longitudinal axis 134 can be perpendicular to the wall 116 (including the surface 120 of the wall 116). In various embodiments, the wall 116 can define a conical space having a collector orifice 128 at one end of the conical space. The collection chamber 132 can be a conical space. The first opening 128 can have its smallest diameter in the range of about 0.1 to about 0.2 mm, about 0.2 to about 0.3 mm, about 0.3 to about 0.4 mm, about 0.4 to about 0.5 mm, about 0.5 to about 1 mm, about 1 to about 2 mm, or greater than about 2 mm.

[0082]

[0102] The collection chamber 132 may be in fluid communication with a pump that may be part of the plasma torch assembly 100. Because of the sealed connection, the plasma zone 124 is not exposed to the atmosphere when the pump is operating and the collection chamber 132 is at vacuum pressure or a higher pressure (e.g., 1 atmosphere).

[0083]

[0103] The pressure upstream in the plasma zone 124 can be higher (e.g., 1-10 atm, including 1.2 atm). In various embodiments, a pressure gradient between the plasma zone 124 and the collection chamber 132 creates a plasma jet that flows into the collection chamber 132, where an apparatus for analysis of the jet can be installed. For optical emission spectroscopy (OES), the apparatus can operate at 1 atm, if desired. OES can also operate at a pressure difference of 0.1 atm between the zones 124 and 132. And for inductively coupled plasma mass spectrometry (ICP-MS), the pressure in the collection chamber can be sufficiently low as required by the mass spectrometer (e.g., 3 Torr in the first section of the zone 132). The pressure in an ICP-MS collection chamber is usually not uniform. Multiple vacuum compartments can be used in mass spectrometry to facilitate differential pumping and gradual reduction of pressure to a level where ions can be mass spectrometrically analyzed and detected.

[0084]

[0104] In various embodiments, one or more channels may be formed in the wall 116 in fluid communication with the plasma zone to receive the exhaust stream (e.g., one or more gases introduced into the plasma torch and / or plasma effluent). In various embodiments, the exhaust stream may be at least partially returned to the plasma zone (e.g., after appropriate filtration). In other embodiments, the exhaust stream may be directed to an exhaust system (e.g., a fume hood). In various embodiments, the exhaust gas may be compressed or liquefied (e.g., via directing the exhaust stream to a compressor or liquefier station), and the compressed or liquefied exhaust gas may be stored and utilized in applications where low grade use of gas is acceptable. For example, in some laser ablation imaging cytometry configurations, after a single pass, contamination of an inert gas (e.g., argon) is typically less than about 2 ppm in dry plasma mode. With such low contamination of impurities, the gas may still be usable for a wide variety of applications (e.g., in some welding applications).

[0085]

[0105] The use of a sealed torch not only allows for cooling the exhaust gas but also for reducing the exhaust gas flow rate (e.g., via at least partial recirculation of the exhaust gas back to the plasma zone), thereby allowing the residual exhaust stream to be exhausted using a much more economical manner than is possible in conventional plasma torch assemblies that are open to atmospheric pressure. As an example, the cooling of the exhaust gas in various embodiments of the torch assembly according to the present teachings can reduce the gas temperature to less than about 100° C., while the exhaust gas in a conventional torch assembly can exhibit a temperature at least an order of magnitude higher before the plasma gas is mixed with air and cooled. Furthermore, in various embodiments, the exhaust gas flow rate in a torch assembly according to the present teachings can be as low as about 15 sLpm, while the exhaust flow rate in a conventional plasma torch assembly can be about 150 times higher because the hot plasma gas is diluted with air to cool it before being directed to the exhaust duct. The ability to operate the torch assembly according to various embodiments at low exhaust flow rates provides a convenient and inexpensive way to handle the exhaust (eg, via directing the exhaust flow into a conventional fume hood).

[0086]

[0106] 1A, in this embodiment, the wall 116 defines a first channel 136 having a plurality of openings, inlet openings 140 (also referred to herein as second openings 140), that provide fluid communication between the first channel 136 and the plasma zone 124. In this embodiment, the first channel 136 may function as an exhaust channel by receiving gases and other plasma effluents from the plasma zone via the inlet openings 140. The first channel 136 includes an outlet opening 141 through which the exhaust flow exits the channel. In this embodiment, the exhaust flow is received by an exhaust system (e.g., a fume hood) that discards the exhaust flow without returning the exhaust flow (or a portion thereof, e.g., the gas employed to generate the plasma) to the plasma zone 124.

[0087]

[0107] In this embodiment, the wall 116 defines another channel 148 that is in fluid communication with the plasma zone 124 through an inlet opening 152. Similar to the channel 136, the channel 148 may also function as an exhaust channel. In particular, the channel 148 includes an exit opening 149 through which the exhaust flow may exit the channel 148.

[0088]

[0108] As discussed in more detail below, each channel 136 and 148 may also function as a recirculation channel to return at least a portion of the inert gas in the exhaust stream back to the plasma zone, e.g., after filtering. Flow in each of the channels 136 and 148 may be independently controlled via two valves 137 and 139, respectively. Regulators 137a and 139a, in communication with the outlets of channels 136 and 148, may adjust the valves to control the flow rate through channels 136 and 148, respectively. A controller 2000 is in communication with the regulators to send control signals to the regulators for controlling their operation.

[0089]

[0109] In this embodiment, the wall 116 defines cooling channels 144a / 144b formed therein and in communication with a cooling unit 1002 that may include a coolant (e.g., water, glycol, and / or other coolant) supplier and provide a recirculating flow of coolant to the channels 144a / 144b. Neither channel 144a nor channel 144b is in fluid communication with the plasma zone, i.e., the two channels are fluidly isolated from the plasma zone.

[0090]

[0110] The flow of coolant through cooling channels 144a and 144b not only provides cooling for wall 116, but also for cooling the exhaust air flowing through exhaust channels 136 and 148. As noted above, cooling the exhaust air can advantageously reduce its temperature, which in turn allows for handling of the exhaust air in ways that are impractical in conventional systems.

[0091]

[0111] In this embodiment, the torch envelope 104 is robustly coupled to the wall 116 of the collection envelope 112. In particular, an O-ring seal 122, including a groove 122a formed in the wall 116 in which an O-ring 122b is seated, provides a robust sealed connection between the wall 116 and the torch envelope 104. Whereas in conventional systems, a gap between the torch envelope and the wall of the collection chamber allows leakage of gas to the outside environment, in this embodiment, there is no gap between the torch envelope and the wall 116, and therefore the O-ring seal 122 prevents such leakage. The robust connection also simplifies the connection of the plasma torch to the wall of the collection chamber. Furthermore, the sealed connection between the torch envelope and the wall of the collection chamber allows for operating the plasma at pressures other than atmospheric pressure. Such flexibility provides several advantages. For example, prior to ignition of the plasma, the pressure within the plasma torch can be reduced (e.g., to a pressure within the range of about 0.1 Torr to about 300 Torr (corresponding to a pressure within the range of about 13.3 Pa to about 40,000 Pa)) to permit the use of an RF coil to ignite the plasma without the need for a conventional ignition coil. Once the plasma is ignited, the pressure within the plasma torch can be increased while the RF radiation generated by the RF coil provides sufficient power to sustain the plasma. By way of example, and not limitation, the pressure within the plasma zone can be greater than 1 atm (2 or 3 atm (2×10 5 Or 3 x 10 5 The pressure can be increased to 10 Pa, etc.

[0092]

[0112] Thus, in this embodiment, the torch envelope 104 is rigidly coupled to the openings 128, 140, 152 and / or the wall 116. The torch envelope 104 may be in direct contact with the O-ring 122, the wall 116 and / or the collection envelope 112. The O-ring 122 may be in direct contact with the collection envelope 112. The rigid coupling between the torch envelope 104 and the collection envelope 112 does not allow movement of the torch envelope 104 relative to the collection envelope 112 without breaking the sealed connection. For example, in various embodiments, the torch envelope 104 is not coupled to the collection envelope 112 by a bellows-type connection or another XY adjustment mechanism that may allow movement of the torch envelope relative to the collection envelope.

[0093]

[0113] With continued reference to FIG. 1A, the torch assembly 100 further includes a gas injector 176 extending from an inlet 176a through which an injector gas can be received and an outlet 176b through which the injector gas can exit the injector 176 and reach the plasma zone 124 where an inductively coupled plasma can be formed. Additionally, a sample for which analytical analysis (e.g., via mass spectrometry) is desired can be delivered through the inlet 176a of the injector 176 and delivered to the plasma zone 124 through the injector outlet 176b along the longitudinal axis 134 of the plasma torch assembly. For example, the injector gas flowing through the injector can carry the sample to the plasma zone. As an example, the sample can be in the form of a suspension of small (e.g., about 1 to about 20 micrometers in diameter) droplets, or dry molecules or an aerosol introduced into the injector can be carried by the gas to the plasma zone. As an example, the source of the sample may be a nebulizer capable of generating an aerosol of a liquid sample (including a sample having biological cells), a laser ablation system for providing a plume of ablated material, or a gas chromatography effluent.

[0094]

[0114] One or more analytes in the sample may be ionized or excited through passage through the plasma zone as a result of their interaction with the plasma. The ions or excited species pass through the sampler orifice 128 to the downstream analyzer. Additionally, at least a portion of the injector gas may pass through the sampler orifice 128. In some cases, some or all of the injector gas passing through the sampler orifice 128 may be collected through the vacuum system of the analyzer and returned to the plasma zone. The returned gas will likely require cleaning / scrubbing before it can be reused by the system.

[0095]

[0115] As noted above, in the sealed torches according to various embodiments, the plasma can be self-ignited via application of an RF electromagnetic field at low pressure, which facilitates the use of shorter injectors in the torch assembly. By way of example, in various embodiments, the injector can have a length in the range of about 5 mm to about 50 mm (e.g., in the range of about 5 mm to about 10 mm, or in the range of about 10 mm to about 20 mm, or in the range of about 30 mm to about 40 mm, or in the range of about 20 mm to about 30 mm, or in the range of about 40 mm to about 50 mm).

[0096]

[0116] The boundaries of the plasma zone 124 are depicted for illustrative purposes only and are not necessarily intended to depict the actual boundaries of the plasma zone. In particular, plasmas are not usually completely confined in volumes with sharp boundaries. Furthermore, there are thermal gradients within an ICP. For example, the center of the plasma may be cooled via the injector flow, thus forming a "center channel" where induction zones outside the channel are hotter and heat from the zones flows into the "center channel."

[0097]

[0117] In this embodiment, the plasma torch assembly 100 includes a bulkhead 180 in the form of a cylindrical structure disposed between the injector 176 and the torch envelope 104. While in this embodiment the torch envelope 104, the injector 176 and the cylindrical structure 180 are disposed concentrically relative to one another, in other embodiments one or more of these structures may be radially offset relative to one or more of the other structures. Additionally, as discussed in more detail below, in various embodiments the injector may be movable in the XY plane (i.e., a plane perpendicular to the longitudinal axis 134). Additionally, although the bulkhead 180 has been depicted as a cylindrical structure, other profiles may be employed, such as a frusto-conical structure.

[0098]

[0118] The positioning of the cylindrical structure 180 between the injector and the torch envelope provides a passageway (also referred to herein as a channel) 182 between the outer surface of the injector 176c and an inner surface 180a of the cylindrical structure 180 having an inlet 182a through which auxiliary gas may be introduced. The auxiliary gas may flow through the passageway 182 to reach the plasma zone 124. Another passageway 183 formed between the outer surface 180b of the cylindrical structure 180 and the inner surface 104a of the torch envelope provides another inlet 183a through which a vortex gas flow (also referred to herein as a plasma gas flow) may be introduced into the interior of the torch envelope. The vortex gas flow may help maintain the plasma in the plasma zone 124 away from the inner surface of the torch envelope and may further facilitate maintaining the plasma near the longitudinal axis 134 of the torch assembly.

[0099]

[0119] In this embodiment, a single source of argon 168 (also referred to herein as the Ar supply) supplies the injector gas, the auxiliary gas, and the vortex gas. Specifically, the Ar supply 168 is fluidly connected to a gas manifold 172, which is in communication with the injectors and channels 182 and 183 via fluid paths 156, 160, and 164, and which distributes a portion of the gas received from the Ar supply via inlets 176a, 182a, 183a into the interior of the torch envelope. While in this embodiment the injector gas, the auxiliary gas, and the vortex gas are the same (i.e., argon), in other embodiments at least two of the gases may be different.

[0100]

[0120] At least one coil 108 (e.g., in the form of multiple coils electrically connected in parallel) is disposed outside the torch and surrounds at least a portion of the plasma zone 124. An RF power supply 125 is in electrical communication with the coil 108 (also referred to herein as an RF coil 108) for applying an RF voltage to the coil 108. Application of the RF voltage to the coil 108 results in the generation of an RF electromagnetic field within at least a portion of the plasma zone. In various embodiments, prior to ignition of a plasma in the plasma zone, the pressure in the plasma zone is maintained at a low pressure (e.g., in the range of about 0.1 Torr to about 300 Torr), and an RF electromagnetic field is utilized to ignite the plasma without utilizing a conventional ignition electrode within or outside the envelope 104. In other embodiments, rather than using an RF electromagnetic field to cause ignition, other mechanisms may be employed, including, for example, a DC or AC electromagnetic field that triggers a breakdown in the presence of the RF electromagnetic field. The ignition trigger electromagnetic field may be provided via additional structures typically implemented for plasma ignition. With a sealed torch, a DC or AC electromagnetic field can be employed to ignite the plasma under low pressure conditions. The reduced pressure and application of an RF electromagnetic field to the plasma zone allows for the use of lower DC or AC ignition voltages and powers, thereby simplifying the ignition circuitry and therefore allowing the use of cheaper and more compact ignition circuitry.

[0101]

[0121] By way of example and without limitation, the RF frequency may be within a range of about 1 MHz to about 10 GHz (e.g., within a range of about 1 MHz to about 300 MHz), and the amplitude of the RF voltage may be within a range of about 50 V to about 6 KV (e.g., within a range of about 300 V to about 1 kV).

[0102]

[0122] As noted, in various embodiments, the exhaust stream, or at least a portion thereof, may be recirculated to the plasma zone. As an example, FIG. 2 shows a plasma torch assembly 200 that is similar to the plasma torch assembly 100 discussed above, but further includes a recirculation path 212 (also referred to herein as a recirculation line 212). The recirculation path 212 is in fluid communication with the outlets of the exhaust channels 136 and 148 and receives the exhaust stream from these channels, including gases that are transferred into the torch assembly via the injector gas flow, the auxiliary gas flow, and the vortex gas flow. The recirculation path routes the received exhaust stream to a gas manifold 208, which in turn routes the gases to the plasma zone. In addition to receiving gases from the recirculation path, the gas manifold 208 also receives gases (e.g., Ar) from a gas supply (not shown in this figure) and distributes the gases received from the gas supply as the injector gas, the auxiliary gas, and the vortex gas for delivery to the plasma zone.

[0103]

[0123] In various embodiments, the recirculation line 212 and / or the gas manifold 208 and the compressor 215 for compressing the exhaust gas may be within the torch envelope housing and / or the RF voltage and / or gas flow control electronics housing. The housing may also include channels for coolant.

[0104]

[0124] By way of further illustration, Figure 1B shows a cutaway view of a wall 300 of a collection chamber (such as wall 116 discussed above in connection with Figure 1A). Wall 300 defines a collector orifice 304, which may be the same as collector orifice 128 depicted in Figure 1A. Collector orifice 304 may open into the collection chamber. Wall 300 may also define openings 308, 312, and 316. Opening 308 may lead to channel 320. Opening 312 may lead to channel 324. Channels 320 and 324 may function as exhaust channels 136 and 148 discussed above for routing gas (e.g., argon) toward an exhaust treatment system or to a recirculation path.

[0105]

[0125] Wall 300 also defines channels 328 and 332 corresponding to coolant channels 144a / 144b through which coolant may be circulated through the wall. Because the wall is formed of a conductive material, it may provide good thermal conductivity, thus allowing the coolant to efficiently extract heat from the exhaust gases flowing into channels 320 and 324.

[0106]

[0126] As discussed above, the wall 300 may also define a groove 336 in which an O-ring may be seated to provide a seal for establishing a sealed connection between the wall 300 and the torch envelope of the plasma torch assembly. The sealed connection may be made by other suitable mechanisms (e.g., by brazing the torch envelope to the surface 300). Alternatively, a portion of the wall 300 may be made of the same material as the torch. In various embodiments, the torch envelope and the wall 300 may be formed of a single unitary element (e.g., by 3D printing or machining a ceramic material). As an example, aluminum nitride and / or Shapal may be particularly suitable for use in various embodiments due to their high thermal conductivity.

[0107]

[0127] 2, in various embodiments, a filter 214 may be placed in the recirculation path to filter the exhaust streams exiting channels 136 and 148 prior to their arrival at gas manifold 172. The filter may separate argon or other inert gas utilized to generate the plasma from other discharge effluents for delivery to the plasma zone. Some examples of filters include, but are not limited to, activated carbon filters, molecular sieve filters, or other suitable filters (including those in PCT Published Application No. WO 2018 / 154512 A1, which is incorporated by reference in its entirety).

[0108]

[0128] In various embodiments, a compressor 215 may be placed in the recirculation path before and / or after the filter 214 to compress the recirculated gas prior to its delivery to the gas manifold 208. Compression of the gas may be accomplished using a wide variety of mechanisms. By way of example, any suitable pump may be utilized, such as a micro-turbine pump, a micro-Scroll pump, a micro-Roots blower, a diaphragm pump, a centrifugal blower, or the like.

[0109]

[0129] In various embodiments, gas flowing through the sampler orifice received by the analyzer may be directed to an exhaust treatment system (e.g., a fume hood) or compressed and stored as a low-grade gas for use in other applications, while gas flowing through the exhaust channels 136 and 148 may be recirculated via recirculation path 212. Such an arrangement is referred to herein as "partial recirculation." In other embodiments, gas flowing through the sampler orifice may be captured, filtered (e.g., by using a filter similar to filter 214), and then returned to the gas manifold, and gas flowing into the exhaust channels 136 and 148 may also be recirculated, optionally filtered, and compressed and returned to the gas manifold. Such an arrangement is referred to herein as full recirculation. Such a gas recirculation arrangement allows for the use of a much smaller gas supply 168, which in some cases may last for months of operation.

[0110]

[0130] 1A, 1B and 2 show the collection orifice (e.g., aperture 128 or aperture 304), exhaust channel (e.g., channel 136 / 148 or channel 320 / 324), and cooling channel (e.g., channel 144a / 144b or channel 320 / 324) in an integral piece. However, such components may be in separate pieces. For example, the collection orifice, exhaust channel, and cooling channel may be in three separate pieces that are then fastened together. In various embodiments, the exhaust channel and cooling channel may be in one integral piece, and that piece may be fastened to the piece with the collection orifice and also to the torch envelope. In various embodiments, the exhaust channel, cooling channel, and torch envelope may be integrated together as one piece and made of the same material (e.g., a machinable ceramic such as Shapal). In other embodiments, the torch envelope and cooling channels may be integrated together as one piece, and the sampling orifice and exhaust channels may be integrated as another piece.

[0111]

[0131] While conventional plasma torches are limited to operating at atmospheric pressure, the sealed connection between the torch envelope and the collector wall in various embodiments of the present teachings provides flexibility in adjusting the operating pressure within the plasma zone. For example, as discussed above, the pressure can be reduced prior to ignition of the discharge to allow for self-ignition using only the electromagnetic field provided by one or more RF coils. Furthermore, after ignition, the pressure can be increased to a value greater than atmospheric pressure. Thus, a torch assembly according to the present teachings can be operated over a wide pressure range, e.g., a pressure range extending from about 0.1 to about 20 atm. The torch assembly can be configured to operate at pressures higher than those typically used with semiconductor ICP processing. For example, the torch assembly can be configured to operate at pressures of about 0.1 to about 0.5, about 0.5 to about 1, about 1 to about 5, about 5 to about 10, or about 10 to about 20 atm. As a result of the different operating pressures, the torch envelope dimensions (e.g., wall thickness), collection envelope dimensions (e.g., collector orifice diameter, other opening diameters), pump speeds, and / or flow rates may differ from those at lower pressures (e.g., 0.01 atm).

[0112]

[0132] The torch assembly may include any of the configurations described herein, including those shown in Figures 5A, 5B, 5C and 6A and 6B, and Figures 8-14.

[0113] Plasma Positioning

[0133] In a standard outdoor torch, the area where sample ionization (e.g., for mass spectrometry) or excitation (e.g., for optical emission spectrometry) occurs may be misaligned with respect to the longitudinal axis of the torch. Reasons for misalignment may include, for example, convective forces that pull the plasma upward (in configurations where the torch axis is at an angle to the direction of gravity), imperfect symmetry of the load coil that can tilt the plasma with respect to the axis, asymmetric introduction of argon into the torch, and imperfections in factors that affect torch performance (injector inner piping, injector tilt and offset, collector orifice, plasma vortex, etc.). Thus, XY positioning of the ICP torch with respect to the collector orifice is important to maximize the analyte signal and minimize the Ar and Ar2 ion signals. In systems with conventional outdoor torches, XY positioning is usually achieved by two-dimensional mechanical motion of the torch with respect to the collector.

[0114]

[0134] As previously described, in the sealed torches according to various embodiments, the torch envelope is rigidly connected to the collector wall, thus preventing XY movement of the torch envelope relative to the collector wall for alignment purposes. Although a movable seal may be utilized that would facilitate such XY adjustment, the movable seal mechanism may be complex and therefore prone to failure. The inability to perform such XY positioning would make a sealed torch configuration in which the torch envelope is rigidly connected to the collector wall impractical. However, the present disclosure provides several approaches that may be employed to adjust the location of the optimal collection area relative to the collection orifice of a collector having a sealed torch according to various embodiments.

[0115]

[0135] For example, referring to Figures 1A and 1B and 3A, the position of the plasma relative to the longitudinal axis of the plasma torch can be adjusted by regulating the flow of exhaust through the exhaust channels 136 and 148. Because the exhaust channels 136 and 148 are symmetrically positioned relative to the collector orifice 128 along the X axis, the plasma can be moved along the X direction by modifying the flow rate of exhaust through these channels, i.e., by establishing a differential flow rate through these channels. Valves 137 and 149 operating under the control of the controller 2000 can be utilized to adjust the flow rate through the exhaust channels 136 and 148. For example, the pressure difference can compensate for factors such as asymmetry of the exhaust inlet relative to the collector orifice or differences in the flow conductances provided by the exhaust channels, among others.

[0116]

[0136] Referring to FIG. 3B, in various embodiments, four exhaust channels 136, 148, 136a, and 148a are provided in the collector wall to allow independent X and Y adjustment of the position of the plasma relative to the longitudinal axis of the torch assembly. For example, as shown in FIG. 3B, the inlets of channels 136 and 148 can be positioned symmetrically with respect to the collector orifice along the X direction, and the inlets of channels 136a and 148a can be positioned symmetrically with respect to the collector orifice along the Y direction. Adjustment of the exhaust flow rate through channels 136 and 148 can be utilized to adjust the position of the plasma along the X direction, and adjustment of the exhaust flow rate through channels 136a and 148a can be utilized to adjust the position of the plasma along the Y direction. Such independent adjustment of the plasma is advantageous because it can facilitate optimization of the analytical signal generated by a downstream analyzer (e.g., a mass spectrometer).

[0117]

[0137] In various embodiments, five or more exhaust channels may be provided in the collector wall to provide additional degrees of freedom for adjusting the position of the plasma, for example, relative to the longitudinal axis of the torch assembly. As an example, Figures 4A and 4B show a schematic demonstration of positioning the plasma by adjusting the exhaust flow through six exhaust channels distributed at the same radial distance around the collector orifice. Each of the exhaust channels may be a channel similar to channel 136 or 148 discussed above in connection with Figure 1A.

[0118]

[0138] 4A shows a situation when the gas flows through the exhaust channel are approximately equal to center the plasma with respect to the longitudinal axis and to promote delivery of ions or excited species to the collector orifice. In some cases, the plasma may not be necessarily centered in this situation, and therefore the XY position may need to be adjusted to increase the flow to the collector orifice.

[0119]

[0139] If the flow of argon in one of the exhaust channels is reduced, the argon flow may deviate from the equilibrium flow in a direction opposite to the location of the exhaust channel where the flow rate is reduced. In this way, pneumatic XY regulation of the argon flow is possible. FIG. 4B shows reduced flow through two of the six exhaust channels. Proportional valves can be installed at the outlet of each individual exhaust channel to individually regulate the exhaust gas flow, or the channels can be grouped such that two or more channels are regulated by one proportional valve.

[0120]

[0140] The pneumatic XY adjustment of the plasma position disclosed herein offers at least two advantages. First, it eliminates the need for mechanical XY adjustment (which is not possible if the torch envelope is robustly sealed to the collector wall) and simplifies the mechanical construction of the torch. Second, in various embodiments, the valves and / or regulators required to adjust the flow rate of the exhaust through the exhaust channel can be located away from the collector (e.g., connected to the collector by a flexible tube). In this way, the control of the exhaust gas flow can be spatially separated from the torch. This allows independent development of the torch and the gas control system and simplifies the replacement of system parts in case of any damage.

[0121]

[0141] As noted above, in various embodiments of the sealed torch according to the present teachings, it is not feasible to move the torch envelope (also referred to herein as the outer jacket) relative to the collector wall. For example, such movement of the torch envelope may result in seal failure. Alternative XY tuning of the ion signal may be performed by moving the injector (e.g., injector 176 of FIG. 1A) while maintaining the torch envelope in a stationary state. For example, as shown diagrammatically in FIG. 4C, the injector (e.g., injector 176) may be placed on a movable platform 4000 (e.g., an XY motion and tilt platform) that may be moved, for example, to tilt or offset the injector relative to the longitudinal axis of the torch envelope 104 to optimize the passage of ions generated through the interaction of the plasma with the sample into the collector orifice 128 of the collector wall 112 (similar to the previous embodiment, multiple RF coils 108 surround the torch envelope). In particular, ions passing through the collector orifice typically originate from a central channel in the plasma. The central channel is largely dictated by the gas jet delivered by the injector, and therefore the position of the jet and its tilt can be used as parameters to adjust the ion signal. These adjustments compensate for the above-mentioned factors that can move the plasma off-axis.

[0122]

[0142] Another way to simplify the XY adjustment is to eliminate sources of off-axis plasma displacement. As previously mentioned, in a standard open-air torch, off-axis displacement can result from convection forces and external air currents that can pull the plasma away from the longitudinal axis, imperfect symmetry of the load coil that can tilt the plasma relative to the longitudinal axis, asymmetric introduction of argon into the torch, and imperfections in the construction of the torch assembly (i.e., precision limitations due to machining techniques). The introduction of gas may not be symmetric as in the embodiments described herein. Furthermore, in various embodiments, the ICP torch may be placed vertically to eliminate gravity effects. In various embodiments, a flat load coil may be used that may be nearly symmetric and thus reduce, preferably eliminate, tilting of the plasma. Thus, in various embodiments, a combination of such approaches (vertical torch, flat symmetric load coil, symmetric introduction of argon) may reduce or eliminate the need for XY adjustment in a closed torch assembly.

[0123]

[0143] Furthermore, as discussed above, a sealed torch assembly may be implemented by using a shorter envelope and / or shorter injectors, which may significantly reduce the need for XY adjustments that may occur due to imperfections in the structure of the torch assembly, for example. In fact, with the reduction in size of the injectors and torches (e.g., to the ranges disclosed herein), the alignment of the parts may be precise enough to eliminate the need for further optimization. For example, a shorter injector may be more precisely positioned inside the torch envelope to provide precise alignment of the injector outlet relative to the collector orifice. The shorter torch piping may also be precisely made (e.g., from a cylindrical or tapered piece of glass or ceramic). Thus, the plasma positioning and the positioning of the central channel in the injector relative to the collector orifice may be precise enough.

[0124]

[0144] In a vertical plasma configuration, the axis of the injector may be aligned with the axis of the torch envelope (e.g., longitudinal axis 134) and the axis of the collector. In a horizontal or tilted plasma configuration, the injector position may be offset or the injector may be tilted to account for the chimney effect (gas flow resulting from buoyancy differences between warm and cold air masses) under optimal operating conditions.

[0125]

[0145] Because the torch envelope may be robustly coupled to the collection envelope, the torch envelope may also be robustly coupled to the exhaust manifold and / or heat spreader.

[0126]

[0146] The collector may dissipate nearly all the plasma heat, reducing the heat load on other elements of the system. Thus, in many embodiments, thermal management of the system may be achieved by focusing primarily on the thermal management of the collector. As discussed above, in various embodiments, thermal management may be provided by coolant flow through coolant channels provided in the collector wall, in which an exhaust channel is also provided. In various embodiments, the exhaust channel and the coolant channel are in sufficient thermal communication (e.g., have sufficient overlap area for heat exchange) such that most of the plasma heat introduced into the collector by the exhaust gas is transferred to the body of the collector and then to a coolant (e.g., water or other coolant, or a heat spreader including fins and / or fans). The heat spreader may include technologies such as heat pipes and flat heat piping surfaces. In this way, nearly all the plasma heat may be managed and removed by the collector. This reduces the heat load on other components of the system.

[0127]

[0147] Because almost all the heat from the plasma goes to the collector, there is no hot exhaust to manage in other elements, and the overall residual heat load on the analytical system is reduced. This relaxes the thermal requirements for the instrument design. This in turn can reduce the number of mechanical fans in the system, thus reducing vibrations that are critical in, for example, a mass cytometry microscope setup.

[0128] Reduced Oxides and Gaseous Contaminants

[0148] In an open-air torch, argon is exhausted into the ambient air. Although argon flows directly through the analysis zone, diffusion of air from the outside into the analysis zone is possible. This can lead to the formation of oxides of metal analytes and increased leakage of gas contaminants from the atmosphere. In various embodiments, a sealed torch according to the present teachings can prevent air diffusion into the torch assembly. Thus, in various embodiments, no mixing of air with argon (or other gases used for plasma) occurs. For example, a seal created between the torch envelope 104 and the collector wall 116 as shown in FIG. 1A reduces, and preferably prevents, mixing of air with gases for plasma.

[0129] Reduced gas emissions

[0149] Some embodiments of plasma torch assemblies according to the present teachings as described herein may significantly reduce gas emissions from instruments utilizing such torch assemblies for ionization and / or excitation of analytes under study. For example, in various embodiments, only about 10-20 sLpm of nearly pure argon may be exhausted. In contrast, in outdoor torches, the hot exhausted argon, including excited and ionized Ar species, is mixed with the atmosphere. This results in the generation of excited or ionized N2, O2, and NO2. X , which can cause the formation of harmful molecules like O3, HCN, CO, CO2. To contain and remove this gas mixture, closed chemical exhausters with an exhaust capacity of about 2000-4000 sLpm are usually used.

[0130]

[0150] In contrast, in various embodiments of the sealed torch described herein, the argon or other gas exiting the collector is already cold and therefore free of or completely free of many excited or ionized species (such as those listed above). However, the collector effluent gas may still contain some reaction products from the injected sample. However, such reaction products may be present in much smaller amounts than the molecules formed from mixing air with the plasma in the open-air torch (since there is no mixing of air with the plasma). A small exhaust of about 10-20 sLpm of cold argon may be sufficient to evacuate the reaction products in the sealed torch collector. Dry plasma operation (e.g., in laser ablation ICP-MS) is particularly attractive when combined with a sealed torch. In the dry plasma mode, there are no bulk reagents (such as water or buffers that can contribute to the generation of harmful and corrosive species in the exhaust gas) that enter the plasma.

[0131] Reduced gas consumption

[0151] As discussed above, in various embodiments, the exhausted gas (e.g., argon) can be reintroduced into the plasma, reducing the total gas consumption (e.g., by a factor of about 5-10). In various embodiments, the sealed torch can consume about 10-20 sLpm of gas for the generation of the plasma. About 2 sLpm of gas can enter through the collector orifice into a vacuum pump associated with a downstream analyzer (e.g., a mass spectrometer). The remaining 8-18 sLpm flow goes to exhaust channels 136 and 148. In a sealed torch, the exhausted gas is not mixed with air, so this gas can be reintroduced into the plasma torch. For example, gas recirculation can be performed as shown in FIG. 2. In this way, in various embodiments, the entire system (e.g., plasma torch assembly and downstream analyzer) can consume only the amount of argon that flows through the collector and into the vacuum pump (e.g., about 2 sLpm in this example), and the total argon consumption can be reduced by about 5-10 times.

[0132]

[0152] This mode of operation may be referred to as partial recirculation since gas leaving the collector is not recirculated. In a full recirculation approach, gas is recirculated not only from the outer plasma gas (e.g., exhaust gas passing through the exhaust channel (e.g., exhaust channel 136, channel 148) rather than through the collector orifice (e.g., collector orifice 128 shown in FIG. 1A)) but also from gas passing through the collector orifice.

[0133]

[0153] In many cases, the gas passing through the orifice of the collector may be contaminated by the sample being analyzed. Thus, in various embodiments, a purification system may be employed to purify the gas (e.g., argon gas) prior to its introduction into the plasma zone via the recirculation path. In the case of partial recirculation, purification of the gas (e.g., argon) may be minimal or may not even be required. In such cases, the complexity and cost of the purification equipment may depend on the level of contamination of the outer plasma gas. In most cases, the argon flow through the collector exceeds the flow from the injector. Thus, most of the analysis flow carried by the injector is sucked into the collector, and therefore only a small portion of the analysis sample components may diffuse into the outer plasma gas flow.

[0134]

[0154] In many cases, since most of the contamination comes from the sample and sample carrier liquid, the contamination may be largely confined to the central channel of the plasma, which is ultimately drawn off by the collector. As an example, in a typical operating situation, about 1 sLpm of gas (e.g., argon) is supplied by the injector, and 2 sLpm is drawn off by the collector. Thus, the collector absorbs not only the injector flow, but also any surrounding plasma that may be contaminated by diffusion of sample material from the central channel. Yet, the outer gas (e.g., argon or other outer gas) may be relatively clean.

[0135]

[0155] As discussed above, if necessary, the recirculated gas may be further purified (filtered) before being reintroduced into the plasma zone (e.g., as a cooling plasma gas). Because no plasma gas is wasted in such a configuration, in various embodiments, a higher flow rate of the vortex gas (e.g., a flow rate of about 50 sLpm) may be employed (e.g., to provide better cooling of the walls of the torch envelope). A high flow rate of the vortex gas (e.g., argon) (e.g., a flow rate of about 50 sLpm) may increase the separation between the walls of the torch envelope and the induction zone in the plasma. This in turn may reduce heat flow to the torch envelope.

[0136]

[0156] The recirculation of argon can benefit from dry plasma operation (such as laser ablation or introduction of dry LIFTed material such as whole cells). In dry plasma mode, the vortex gas stream (e.g., argon) introduced into the torch assembly is unlikely to be contaminated. Even if a small amount of another gas (e.g., helium) is introduced into the injector, most of the other gas (e.g., helium) may remain in the central channel. The remainder may enter the recirculated gas. This remainder may be a small contribution to the total gas (e.g., argon) in the recirculated stream and is therefore unlikely to significantly alter the characteristics of the induction zone. Thus, the system may operate as is or with minor adjustments to compensate for such impurities being recirculated back to the plasma zone.

[0137] Delete the gate valve

[0157] In various embodiments, a gate valve may not be required in the analyzer receiving ions or excited species from a sealed torch according to the present teachings. When the ICP torch is turned off, the plasma temperature drops rapidly and the gas density near the collector orifice increases rapidly. As a result, the mass flow through the collector orifice may increase significantly (by about four times). The mass flow through the vacuum system of the downstream analyzer (e.g., mass spectrometer) may also increase significantly. This mass flow may load the vacuum system beyond the capacity of the turbomolecular and roughing pumps to maintain steady operation. A gate valve between the interface and the mass spectrometer is usually installed with an open-air torch. The gate valve may be closed before the plasma is disabled.

[0138]

[0158] In various embodiments of the sealed torches described herein, turning off the plasma can be accomplished by stopping or reducing the flow of gas (e.g., argon) into the torch. Because the torch is sealed from the atmosphere, in the plasma-off condition the interior of the torch envelope can be evacuated or partially evacuated, thus preventing excessive gas load on the vacuum system of a downstream analyzer (e.g., a mass spectrometer), thus eliminating the need for a gate valve.

[0139]

[0159] In various embodiments, a dry sample can be ablated in the ablation cell, and the products of the ablation can then be mixed with a gas flow and pumped through the injector. In various embodiments, the sample can be introduced into a suspension that includes droplets and aerosols. To prevent gas flow through the injector, a mechanical plug can be used to block input into the injector in the ablation cell. Alternatively, a mini-gate valve blade can be placed in the injector path. Even without the mini-gate valve, if the auxiliary flow and vortex flow are stopped, the only gas entering the torch will flow through the injector. However, the injector opening is usually smaller than the opening in the collector.

[0140]

[0160] Thus, the injector size will limit the flow of gas into the vacuum system. For example, with a typical collector inner diameter (ID) of 1 mm and an injector ID of 0.5 mm, the flow of gas into the vacuum system will be 4 times lower when a sealed torch is installed than with an open-air torch. With an open-air torch, the atmosphere will go directly to the collector when the plasma is off, which may then overload the vacuum pumping system. With a sealed torch, the atmosphere is prevented from reaching the collector orifice. Furthermore, if the injector is connected to the ablation cell (which is also sealed), without plasma gas, the pressure in the ablation chamber will drop, resulting in nearly no load on the vacuum system without plasma during operation. The sealed torch described herein allows this reduced load because the sealed torch, injector, and ablation cell are part of the sealed vessel.

[0141]

[0161] Control of vacuum pump overload can be particularly simple in systems with a recirculating outer plasma gas (outer vortex gas). In such a recirculating system, the flow rate of gas (e.g., argon) into the sealed torch can be approximately matched to the flow rate (e.g., 2 sLpm) of gas (e.g., argon) entering the collector through its orifice under normal plasma operation. If the plasma is off, the gas (e.g., argon) supply is maintained at the same flow rate, thus producing approximately no change to the pumping load. In various embodiments, the recirculation flow of the vortex gas can be as high as 50 sLpm, but since the torch is a closed circuit system, the recirculation flow does not contribute to the total pressure in the torch. As discussed above, the closed circuit system is sealed and can include partial recirculation of the plasma (vortex) gas. With plasma operation, the pressure in the torch can be at a set point controlled by the flow rate, the temperature of the plasma, and the opening in the collector. During operation, the pressure can be 1 atm or 1.2 atm or 0.8 atm or even 2-20 atm depending on the operator needs and the opening in the collector. With the plasma off, the pressure in the torch housing can drop to a level that balances the input flow from the mass flow controller (source) and the output flow through the opening in the collector (sink).

[0142] Self-ignition of plasma by RF electromagnetic fields.

[0162] As discussed above, in various embodiments, no ignition electrodes and their electronics may be required to ignite the plasma in a sealed torch according to the present teachings. In particular, the plasma may be self-ignited at low pressure using only an RF electromagnetic field generated by an RF powered RF coil. In contrast, in an outdoor torch, the plasma cannot be automatically ignited when argon or other gas is introduced into the torch and a high voltage is applied to the load coil. In an outdoor torch, the pressure in the plasma zone is at or near atmospheric pressure, increasing the required breakdown voltage to ignite the plasma. To ignite the plasma, a seed high voltage spark is usually used. This spark requires an additional electrode mounted inside or outside the plasma torch as well as electronics for the spark discharge.

[0143]

[0163] In a sealed torch, the pressure of the argon or other gas can be easily reduced to a few Torr. At such low pressure, the plasma can be self-ignited if a suitably high voltage is applied to the load coil. A suitably high RF voltage can be supplied by the RF power supply 125 once the pressure in the sealed torch is reduced. Thus, no ignition electrode or additional ignition electronics need be used in the sealed torch.

[0144] Short injector

[0164] In various embodiments, a short injector may be employed, for example, as a result of the lack of need for igniter hardware and / or mechanical XY adjustments and / or the use of a compact solid-state RF generator. For example, no space for extra hardware is required between the sample and the torch. A short injector may result in earlier arrival of the sample (e.g., laser ablation plume) in the plasma and consequently less spread of the resulting transient.

[0145]

[0165] In various embodiments, the minimum length of a sealed torch according to the present teachings can be determined by the size of the load coil and can be estimated as the coil thickness plus the diameter of the coil windings based on empirical (or modeling) rules of how the external conductor interacts with the magnetic field created by the load coil and the plasma. A short injector can be installed in the sealed torch envelope, and the sample introduced into the torch can be generated, for example, as a laser ablation plume near the torch. The distance from the laser ablation plume to the induction zone can be as short as possible (such as 0.5 cm to 1 cm or 1 cm to 5 cm). This in turn results in faster plume arrival times and a narrower spread of the resulting plume transient.

[0146]

[0166] By way of example, as discussed above, injectors having lengths in the range of about 5 mm to about 50 mm may be used in various embodiments described herein. By way of example, the use of an injector having a length of about 18 mm should result in a reduction in the diffusive spread of the ablation plume of about 20× compared to commercial ICP torch systems based on the open-air torch design used for application of laser ablation ICP MS.

[0147]

[0167] Additionally, as discussed in more detail below, in various embodiments, the auxiliary gas flow may be eliminated, allowing the injector to be moved closer to the collector orifice. In various embodiments, the injector may be mounted on a metal base and formed of a metal injector or may have a metal injector jacket to facilitate dissipation of plasma heat flowing into the injector. In some such cases, the injector may have a conical envelope with a cross-sectional area that decreases from its inlet to its outlet to reduce the mass of the portion of the injector closer to the plasma while reducing any potential disturbances caused by the metal parts of the injector to the RF electromagnetic field, thereby providing more efficient thermal management of the injector.

[0148] Independence from atmospheric pressure

[0168] The sealed torch described herein has an ICP pressure that is independent of atmospheric pressure, enhancing measurement repeatability and making the measurement independent of instrument altitude.

[0149]

[0169] In an open ICP torch, the exhaust argon exits to the open atmosphere. As a result, the gas pressure in the plasma may be equal to or dependent on atmospheric pressure. Atmospheric pressure may vary, for example, from day to day and may depend on the altitude of the instrument operation site. These variations reduce the repeatability of the measurements. Both the temperature of the plasma and the amount of sampled gas (e.g., argon) may vary depending on the pressure in the torch. In various embodiments of the sealed torch described herein, the pressure may be controlled independently of the atmospheric pressure. In this way, the repeatability of the measurements may be improved. Furthermore, when the plasma is ignited by using an RF coil, the pressure in the plasma torch may be increased above atmospheric pressure (e.g., to avoid the ingress of contaminants from the outside air). However, the operation of a sealed torch according to the present teachings is not limited to pressures above atmospheric pressure. Rather, in various embodiments, a sealed torch according to the present teachings may be operated at or below atmospheric pressure. Still, in some circumstances, operating significantly above 1 atm may be preferable to increase the density of the plasma.

[0150]

[0170] 4D, in various embodiments, the sealed torch assembly may be housed within a housing 400. The housing 400 may be formed, for example, of metal, to protect the sealed torch assembly and RFG from radiated electromagnetic interference. Additionally, cooling channels may be formed within the housing. Passage of a coolant (e.g., water) through such cooling channels may dissipate heat generated by the torch plasma and / or other system components.

[0151]

[0171] In various embodiments of a sealed torch assembly according to the present teachings, the auxiliary gas flow can be eliminated. This allows for a more compact construction of the torch assembly as discussed below. For example, Figure 5A illustrates a cross-section of a sealed torch 500 including a torch envelope 502 in the form of a cylindrical tube including a back wall 502a and a cylindrical outer wall 502b. As in the previous embodiment, the torch envelope 502 is rigidly connected to the wall 504a of the collector 504 around the orifice 504b of the collector envelope via a sealed connection.

[0152]

[0172] A conical injector 506 is placed within the housing provided by the torch envelope 502. The injector 506 extends from an inlet opening 506a, through which gas carrying the sample can be introduced from within the injector to an exit opening 506b, through which gas entrained with the sample can exit the injector and enter the plasma zone.

[0153]

[0173] A vortex generator 508 is coupled to the torch envelope 502 and receives a vortex gas (which may be the same as or different from the injector gas) from a gas supply and delivers the gas to the inner radially outer portion of the torch envelope 502. The gas flow delivered by the vortex generator exhibits a plurality of vortices that may help confine the generated plasma within a plasma zone (shadow area) near the longitudinal axis of the torch envelope.

[0154]

[0174] One or more RF coils 510, such as the RF coils described above, surround a portion of the torch envelope. An RF power source (not shown in this figure) applies RF power to the coils to generate an RF electromagnetic field in the plasma zone. As with the previous embodiment, the RF coils can be utilized to ignite a plasma 519 in the plasma zone at low pressure. Following ignition of the plasma, the pressure in the torch envelope can be increased while the RF electromagnetic field helps to sustain the plasma.

[0155]

[0175] The injector gas exiting the injector carries the sample through the plasma where one or more analytes in the sample are ionized and / or excited. The gas flow further carries the ions and / or excited species through orifice 504b to the analysis zone of a downstream analyzer (e.g., a mass spectrometer).

[0156]

[0176] An exhaust channel 512 is in fluid communication with the interior of the torch envelope to remove the vortex gases and any potential plasma effluent that may have mixed with the vortex gases from the torch envelope. The majority of the vortex gases exit the torch envelope via the exhaust channel 512. As with the previous embodiment, the exhaust gases may be recirculated or disposed of without recirculation.

[0157]

[0177] There are significant structural differences between the torch assembly 500 and conventional torch assemblies. For example, the sealed connection between the torch assembly and the extractor wall allows the axial length of the torch assembly to be shortened. As an example, in various embodiments, the axial distance between the back plate of the torch assembly and the orifice of the extractor envelope can be about 3x or less than the inner diameter of the torch envelope. This in turn allows the length of the injector to be shortened and the axial distance between the injector outlet and the orifice to be shortened. As an example, the length of the injector can be in the range of about 5mm to about 50mm, and the distance between the injector outlet and the orifice can be in the range of about 5mm to about 40mm. Additionally, in this embodiment, the injector is completely enclosed within the interior of the torch assembly such that a portion of the injector protrudes into the plasma. The conical shape of the injector helps reduce heating of the injector by the plasma. Additionally, at least a portion of the injector (e.g., the outer surface) may be formed of a material (e.g., a metal) that exhibits good thermal conductivity that may facilitate heat dissipation, thus enabling the injector to withstand the high plasma temperatures to which it is exposed.

[0158]

[0178] The conical shape of the injector, as well as the proximity of the back wall of the torch envelope to the plasma, and its positioning relative to the orifice of the collector envelope, facilitates propelling the plasma forward toward the collector, where the ions and / or excited species can be introduced into a downstream analyzer.

[0159]

[0179] By way of further illustration, FIG. 5B generally depicts a cross-sectional view of another embodiment 514 of a torch assembly according to the present teachings that does not employ an auxiliary gas flow. As with the previous embodiment, the torch assembly 514 includes a torch envelope 516 that is robustly sealed to the collector wall around the collector orifice. The torch assembly 514 also includes an injector 518 for injecting an injector gas that can carry the sample to the plasma generated in the plasma zone, and a vortex generator that can generate a vortex gas flow within the outer radial portion of the torch envelope (which can help confine the plasma near the longitudinal axis of the torch envelope). Additionally, as with the previous embodiment, an exhaust channel 520 is in fluid communication with the interior of the torch envelope for removing a majority of the vortex gas introduced into the torch envelope.

[0160]

[0180] Unlike the previous embodiment, the torch envelope has a frusto-conical profile with a cross-section that widens in the direction of the collector orifice (which may help propel the plasma toward the collector orifice). Furthermore, in this embodiment, the injector is not fully contained within the enclosure provided by the torch envelope. Rather, the injector protrudes partially into the interior of the torch envelope. As a result, while close to the plasma, the injector does not protrude into the plasma. In addition, the injector has a cylindrical profile. The conical shape of the injector and the closer proximity of wall 502a to the collector orifice may collectively eliminate the need for an auxiliary gas.

[0161]

[0181] FIG. 5C shows another example of a plasma torch assembly 522 according to an embodiment in which an auxiliary gas flow is not utilized. The plasma torch assembly 522 includes a torch envelope 524, an injector 526, a vortex generator 528, and an exhaust channel 530 connected via a robust seal to the collector envelope. As in the previous embodiment, the distance between the backplate of the torch envelope and the collector orifice is shortened relative to the conventional system. Furthermore, the outlet of the injector is closer to the collector orifice than in the conventional system. In this embodiment, the injector protrudes partially into the interior of the torch envelope and has a cylindrical profile. The torch envelope has a curved profile with a varying radius of curvature that decreases in a nonlinear manner from the end of the torch envelope that is robustly sealed to the collector envelope to the end that is coupled to the injector. The tapered profile of the torch envelope is such that the cross-sectional area of ​​the torch envelope increases from the end that is coupled to the injector to the end that is robustly sealed to the collector envelope. More generally, the cross section (R) of the torch envelope may vary in any suitable manner as a function of distance (z) along the longitudinal axis of the torch envelope. The tapered profile of the torch envelope helps to direct vortices and propel the plasma toward the collector orifice in a manner that may more efficiently confine the plasma closer to the longitudinal axis of the torch envelope.

[0162]

[0182] example

[0183] Example 1

[0184] Figure 6A shows an image of a sealed plasma torch assembly according to one embodiment, and Figure 6B shows the sealed plasma torch assembly of Figure 6A with the plasma on and the load coil visible.

[0163]

[0185] Example 2

[0186] 8 shows an image of the torch envelope 704 and the harvest envelope 708. The torch envelope 704 is made of ceramic and has a trumpet-like shape. The torch envelope 704 has a section with an inner diameter 712 and flares out from the inner diameter 712 to a larger inner diameter 716. In this case, the length of the section of the torch envelope with the inner diameter 712 is about 80% of the total length of the torch envelope 704. In general, the length of the section of the torch envelope with the inner diameter 712 can be 99%-90%, 90%-80%, 80%-70%, 70%-60%, 60%-50%, 50%-40%, 40%-30%, 30%-20%, 20%-10%, or 10%-1% of the total length of the torch envelope 704. The sampling envelope 708 includes a sampling orifice 720 and an opening 724 for an exhaust channel. Several outputs of the exhaust channel 724 (including an exhaust output 728) are shown with the sampling envelope 708.

[0164]

[0187] Example 3

[0188] 9 shows a diagram of a sealed torch assembly 800 that includes a supply (i.e., source) of sample for analysis. Sample supply can be via a nebulizer to generate an aerosol of liquid sample (including samples with biological cells), a laser ablation setup to supply a plume of ablated material, or a gas chromatography effluent.

[0165]

[0189] The sealed torch assembly 800 also includes an injector for supplying the sample (eg, in the form of an aerosol and gaseous material including a carrier gas), and the sample in the form of particles, molecules and / or atoms.

[0166]

[0190] Also shown is a plasma gas supply manifold, the purpose of which is to create a desired pattern of gas flow that aids in the desired induction zone (e.g., plasma zone) and cooling within the torch envelope of the sealed torch assembly 800. The torch envelope can be an enclosure that confines the plasma and prevents its contact with the outside environment (e.g., air).

[0167]

[0191] The sealed torch assembly 800 includes an RF load coil for generating an RF electromagnetic field to ignite and sustain a plasma.

[0168]

[0192] The sealed torch assembly 800 also includes an exhaust manifold for removing most of the gases supplied by the plasma gas manifold.

[0169]

[0193] The system may also include a heat spreader / cooler to remove heat generated by the power imparted into the plasma through the RF load coil.

[0170]

[0194] The sampling orifice is shown in the sampling envelope. The sampling envelope is the element that separates the plasma torch zone (including its analytical zone) from the analytical chamber (also the sampling chamber). The sampling orifice allows the passage of the sample (analytical flow) from the analytical zone into the analytical chamber (which can be a vacuum chamber with ion optics for ICP-MS and mass cytometry). The analytical chamber can be a chamber at or around atmospheric pressure for analysis such as ICP-OES.

[0171]

[0195] Example 4

[0196] Figure 10 shows a schematic diagram of a sealed torch assembly 900 that has the same components as the sealed torch assembly 800. However, Figure 10 shows how the module connections can be interfaced with each other. The sealed torch assembly 900 has an axial positioning order of the heat spreader / cooler and exhaust manifold reversed compared to the sealed torch assembly 800.

[0172]

[0197] Example 5

[0198] Figure 11 shows a diagram of a sealed torch assembly 1000. The sealed torch assembly 1000 has the same components as the sealed torch assembly 800. Figure 11 shows an embodiment in which the heat spreader (shown as a dashed line) is extended and incorporates the gas supply manifold, load coil, torch envelope, and sampling envelope.

[0173]

[0199] Example 6

[0200] 12 shows a diagram of a sealed torch assembly 1100. The sealed torch assembly 1100 has the same components as the sealed torch assembly 800. The sealed torch assembly 1100 has the positions of the gas supplies and exhaust manifold reversed compared to the sealed torch assembly 800.

[0174]

[0201] Example 7

[0202] 13 shows a diagram of a sealed torch assembly 1200. The sealed torch assembly 1200 has the same components as the sealed torch assembly 800. However, the sealed torch assembly 1200 has a torch envelope that is not cylindrical in shape. In the sealed torch assembly 1200, the torch envelope has a frusto-conical shape.

[0175]

[0203] Example 8

[0204] FIG. 14 shows a diagram of a sealed torch assembly 1300. The sealed torch assembly 1300 has the same parts as the sealed torch assembly 800. In addition, the sealed torch assembly 1300 includes an igniter module. The igniter module can be used to initiate the plasma. As described herein, the ability to seal the plasma chamber creates an opportunity for self-ignition of the plasma by using the RF electromagnetic field of the load coil. Thus, the igniter module can be redundant and is therefore optional. Removing the igniter module results in a simpler and more compact setup. Sealing the torch allows for operation of the igniter at reduced pressures which reduces igniter voltage and power requirements and simplifies the igniter mechanical and electrical setup. Thus, if RF self-ignition is not available due to RF power supply constraints, the lower pressure igniter ignition allowed by the sealed torch reduces the impact of the torch assembly length and the cost of the system.

[0176]

[0205] The sealed torch assemblies or portions thereof shown in FIGS. 6A and 6B and FIGS. 8-14 may be used in plasma torch assembly 100 of FIG. 1A or plasma torch assembly 200 of FIG.

[0177] II. Method

[0206] 7 is a flow chart of an example process 600 associated with an embodiment of a method of analysis using a plasma in a sealed plasma torch. In some implementations, one or more process blocks of FIG. 6 may be performed by an assembly (e.g., the plasma torch assembly 100). In some implementations, one or more process blocks of FIG. 6 may be performed by another device or group of devices separate from or including the assembly. Additionally or alternatively, one or more process blocks of FIG. 6 may be performed by one or more components of the plasma torch assembly 100.

[0178]

[0207] At block 610, a voltage is applied to a coil disposed around the torch envelope. As an example, the coil can be coil 108, and the torch envelope can be torch envelope 104 discussed above in connection with FIG. 1A. For example, a power source can apply a voltage to the coil disposed around the torch envelope. The power source can be an RF generator. The application of the voltage can consume a power in the range of 0.2-1 kW, 1-1.5 kW, 1.5 kW-2 kW, or greater than 2 kW. Gas is introduced into the interior of the torch envelope, and a pressure is maintained within the torch envelope (e.g., in the range of about 0.0001 atm to about 0.4 atm). In other cases, ignition of the plasma can be achieved at elevated pressures (e.g., in the range of 1-5 atm), including conventional pressures (by using an igniter capable of operating at such pressures).

[0179]

[0208] At block 620, a plasma is ignited within the torch envelope by applying an RF voltage to the coil. For example, the voltage applied to the coil may ignite the plasma within the torch envelope as described above. The plasma may be ignited at a pressure within the range of about 0001 to about 0.1, about 0.01 to about 0.1, about 0.1 to about 0.5, about 0.5 to about 1, about 1 to about 5, about 5 to about 10, or about 10 to about 20 atm. During the process of igniting the plasma, the pressure may be any of the pressures described for ignition. Igniting the plasma may not need to include applying a voltage to a conventional ignition electrode inside the torch envelope. For example, with a sealed torch, the plasma may self-ignite via a voltage applied to the RF coil once the pressure within the sealed torch is reduced to a sufficiently low level.

[0180]

[0209] In block 630, a first gas (e.g., argon) is flowed through the torch envelope, where the first gas can carry the sample to the plasma to cause its ionization or excitation. The passage of the gas carrying the sample can generate a plasma effluent. The first gas can flow through the torch envelope at a flow rate of about 0.1 to about 2 sLpm, about 2 to about 5 sLpm, about 5 to about 10 sLpm, about 10 to about 50 sLpm, or more than 50 sLpm. The flow rate of the first gas can be the flow through the injector (e.g., injector 176 in FIG. 1A) or can be the total flow rate of the gas through the torch envelope 104 (e.g., all gas going to the torch envelope via the fluid paths 156, 160, and 164 depicted in FIG. 1A). The first gas can include argon, helium, or any noble gas. The first gas can also be nitrogen or hydrogen or some other suitable gas for sustaining a plasma. In various embodiments, the first gas may exclude oxygen or nitrogen (including proportions present in air). The first gas may exclude air. The plasma effluent may include atoms, ions, and radicals of the first gas and / or samples entrapped within the first gas.

[0181]

[0210] A first gas may be introduced into the torch envelope by flowing a first portion of the first gas through an injector (e.g., injector 176) about a longitudinal axis (e.g., longitudinal axis 134) of the torch envelope. In various embodiments, the sample to be analyzed may be flowed through the injector with a first portion of the first gas. The plasma effluent may include ionized and excited species from the sample. A second portion of the first gas may be flowed through an annular region between the torch envelope and the injector. The annular region may be supplied with gas via fluid path 160 and / or fluid path 164 depicted in FIG. 1A.

[0182]

[0211] At block 640, the gas introduced into the torch envelope (also referred to herein as a second gas) is flowed through a plurality of openings. The plurality of openings may be defined by a surface of a wall. The surface may form a sealed connection with the torch envelope. The wall may be wall 116, and the surface may be surface 120 depicted in FIG. 1A.

[0183]

[0212] At block 650, a first portion of the second gas is flowed through a first opening of the plurality of openings into the collection chamber. The first opening can be the sampler orifice 128 or any collection orifice described herein. The first portion of the first gas flowing through the first opening can have a flow rate of about 0.1 to about 0.5 sLpm, about 0.5 to about 1 sLpm, about 1 to about 2 sLpm, or about 2 to about 5 sLpm.

[0184]

[0213] At block 660, a second portion of the second gas may be flowed through a second opening of the plurality of openings into a first channel defined by the wall. The first portion of the second gas may have a greater percentage of plasma effluent than the second portion of the second gas. The second portion of the second gas may include gas that did not pass through the plasma. The first opening may be closer to a center of the torch envelope than the second opening or other openings of the plurality of openings.

[0185]

[0214] In various embodiments, the process 600 may include increasing the amount of plasma effluent passing through the first opening by adjusting the flow rate of the second gas through the second opening. Positioning the plasma relative to the longitudinal axis of the torch assembly to optimize the passage of the plasma effluent through the collector orifice may be performed as described in connection with FIGS. 4A and 4B. One or more of the flow rates through the openings other than the first opening may be adjusted (e.g., by a valve or mass flow controller). Reducing the flow rate through an opening may move the maximum concentration of plasma effluent away from the opening. Increasing the flow through an opening may move the maximum concentration of plasma effluent toward the opening.

[0186]

[0215] In various embodiments, the process 600 can include recycling a second portion of the second gas back to the plasma (recirculation). As an example, the recirculation can be performed as described with respect to Figure 2. In various embodiments, the recycled gas can be further purified to remove contaminants before being recycled to the plasma.

[0187]

[0216] In various embodiments, the process 600 may include flowing a coolant through a cooling channel defined by a wall of the collector orifice. In various embodiments, the process 600 may include cooling the temperature of the wall to 100° C. or less, including 80° C. or less, 60° C. or less, 40° C. or less. The coolant may include water, glycol, or any other suitable coolant.

[0188]

[0217] In various embodiments, the process 600 can include flowing a remaining portion of the second gas through a remaining opening of the plurality of openings. A flow rate of the second portion of the second gas and the remaining portion of the second gas can be in a range of 2 to 50 sLpm.

[0189]

[0218] Process 600 may include additional implementations, such as any single implementation or any combination of implementations described below and / or in conjunction with one or more other processes described elsewhere herein.

[0190]

[0219] In various embodiments, the first portion of the second gas may contact the sample after flowing through the first opening. More generally, the first portion of the second gas may contact the sample before flowing through the first opening, e.g., the sample may be carried into the plasma zone by the injector flow. The first portion of the second gas may react with the sample. In various embodiments, the first portion of the second gas may include particles originating from the ablated sample. In various embodiments, the first portion of the second gas may include particles in suspension. The results of any reaction between the first portion of the second gas and the sample may be analyzed (including by mass spectrometry or optical emission spectrometry). Collection techniques include Imaging Mass Cytometry™ and Suspension Mass Cytometry.

[0191]

[0220] Although Figure 6 illustrates example blocks of process 600, in some implementations, process 600 may include additional blocks, fewer blocks, different blocks, or blocks arranged in a different manner than depicted in Figure 6. Additionally or alternatively, two or more of the blocks of process 600 may be performed in parallel.

[0192]

[0221] The specific details of the particular embodiments may be combined in any suitable manner without departing from the spirit and scope of the embodiments of the invention, however, other embodiments of the invention may be directed to particular embodiments relating to each individual aspect, or particular combinations of these individual aspects.

[0193]

[0222] The foregoing description of the exemplary embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms described above, and thus many modifications and variations are possible in light of the above teachings.

[0194]

[0223] In the preceding description, for purposes of explanation, numerous details have been set forth to provide an understanding of various embodiments of the present technology. However, it will be apparent to one skilled in the art that some embodiments may be practiced without some of these details or with additional details.

[0195]

[0224] Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, many well-known processes and elements have not been described in order to avoid unnecessarily obscuring the invention. Additionally, the details of any particular embodiment may not necessarily be present in variations of the embodiments, or may be added to other embodiments.

[0196]

[0225] Where a range of values ​​is provided, it is understood that each intermediate value between the upper and lower limits of that range (to one-tenth of the unit of the lower limit unless the context clearly dictates otherwise) is also specifically disclosed. Each smaller range between any stated value or intermediate value in a stated range and any other stated or intermediate value in that stated range is included. The upper and lower limits of these smaller ranges may be independently included or excluded in the range, and each range in which either, neither, or both of the upper and lower limits are included in the smaller range is also encompassed within the invention, subject to any specifically excluded limits in the stated range. Where a stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

[0197]

[0226] As used herein and in the appended claims, the singular indefinite and definite articles include plural references unless the context dictates otherwise. Thus, for example, a reference to "a method" includes a plurality of such methods, and a reference to "the sample" includes a reference to one or more such samples and equivalents thereof known to those skilled in the art, etc. The invention has now been described in detail for purposes of clarity and understanding. However, it will be understood that certain variations and modifications may be practiced within the scope of the appended claims.

[0198]

[0227] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. None of them is admitted to be prior art.

Claims

1. An envelope surrounding the plasma zone, a collection chamber including a wall having at least one collector orifice, the at least one collector orifice providing fluid communication between the plasma zone and the collection chamber; and A plasma torch assembly including a seal for providing a hermetic connection between the envelope and the wall of the collection chamber around the at least one collector orifice.

2. The plasma torch assembly of claim 1 , wherein the seal is configured to robustly connect the envelope to the wall.

3. 10. The plasma torch assembly of claim 1, further comprising an injector extending from a first inlet for receiving an injector gas to a first outlet for delivering at least a portion of said injector gas to said plasma zone.

4. The plasma torch assembly of claim 3 , further comprising an injector gas supply for supplying the injector gas to the injector.

5. 5. The plasma torch assembly of claim 4, further comprising a tubular structure at least partially surrounding the injector and disposed between the injector and an inner surface of the envelope to define a second inlet for delivering auxiliary gas to a region between an outer surface of the injector and an inner surface of the tubular structure, The tubular structure further defines a third inlet for delivering vortex gas to a region between an outer surface of the tubular structure and an inner surface of the envelope.

6. The plasma torch assembly of claim 5, further comprising an auxiliary gas supplier and a vortex gas supplier for supplying the auxiliary gas and the vortex gas.

7. 7. The plasma torch assembly of claim 6, wherein the injector gas, the auxiliary gas and the vortex gas are the same gas and are supplied via a single gas supply.

8. 8. The plasma torch assembly of claim 7, further comprising a gas manifold configured to receive the gas from the single gas supply and to distribute a portion of the received gas as the injector gas, the auxiliary gas, and the vortex gas.

9. The plasma torch assembly of claim 1 , further comprising at least one RF coil disposed at least partially around said envelope.

10. The at least one RF coil is adapted to maintain a pressure within the interior of the torch envelope between about 13 Pa and about 4×10 ４ 10. The plasma torch assembly of claim 9, configured to permit ignition of the plasma in response to application of an RF voltage thereto when the RF voltage is within the range of Pa.

11. 10. The plasma torch assembly of claim 9, wherein the at least one RF coil comprises two or more RF coils electrically connected in parallel.

12. 10. The plasma torch assembly of claim 9, wherein the at least one RF coil has a split coil structure having two or more segments, the two or more segments being mechanically coupled to each other to surround the envelope and electrically coupled to provide an electrical path between the two or more segments.

13. The plasma torch assembly of claim 11 , wherein each of the coil segments has a generally semi-circular profile.

14. 10. The plasma torch assembly of claim 9, wherein the at least one RF coil is axially separated from the collector orifice by a distance of about 1 / 3 or less of a diameter of the RF coil.

15. 10. The plasma torch assembly of claim 9, further comprising a radio frequency (RF) source in electrical communication with the at least one RF coil for generating an RF electromagnetic field within at least a portion of the plasma zone for igniting the plasma.

16. The plasma torch assembly of claim 15, wherein the RF source is configured to apply an RF voltage to the RF coil at a frequency in a range of about 900 kHz to about 10 GHz.

17. The plasma torch assembly of claim 16, wherein the RF voltage has an amplitude in the range of about 50V to about 6 kV.

18. 10. The plasma torch assembly of claim 1, further comprising at least one exhaust channel formed in said wall and extending from an inlet opening to an outlet opening, said inlet opening being in fluid communication with said plasma zone.

19. 20. The plasma torch assembly of claim 18, further comprising at least one exhaust valve operably coupled to the outlet opening of the at least one exhaust channel for controlling exhaust flow exiting the exhaust channel.

20. 20. The plasma torch assembly of claim 19, further comprising at least one regulator coupled to the at least one exhaust valve for regulating a flow rate of exhaust exiting the exhaust channel.

21. 21. The plasma torch assembly of claim 20, wherein the at least one regulator is configured to adjust the exhaust flow rate to optimize a flow of ions or excited species from the plasma zone into the collector orifice.

22. 22. The plasma torch assembly of claim 21, wherein the at least one exhaust channel includes first and second exhaust channels disposed on opposite sides of the collector orifice.

23. 23. The plasma torch assembly of claim 22, wherein the at least one regulator includes first and second regulators operably coupled to the first and second exhaust channels, respectively, for regulating a flow rate of the exhaust exiting the channels.

24. 23. The plasma torch assembly of claim 22, wherein the at least one exhaust channel includes two or more pairs of channels, each of the pairs configured to enable adjusting a position of the plasma along a different dimension via adjusting a flow rate of exhaust gas through the channel of the pair.

25. 25. The plasma torch assembly of claim 24, further comprising a controller in communication with the first and second regulators for adjusting the exhaust flow rates through the first and second exhaust channels to optimize a flow of ions or excited species from the plasma zone into the collector orifice.

26. 26. The plasma torch assembly of claim 25, wherein the first and second exhaust channels are symmetrically positioned about the collector orifice, and the controller controls the regulator to provide approximately equal exhaust flow rates through the first and second exhaust channels.

27. 20. The plasma torch assembly of claim 19, wherein the at least one exhaust channel includes at least two pairs of exhaust channels, at least a first pair of the exhaust channels positioned relative to the collector orifice to enable adjustment of a position of the plasma along one dimension via adjusting a flow rate of the exhaust through the at least first pair, and at least a second pair of the exhaust channels positioned relative to the collector orifice to enable adjustment of a position of the plasma along an orthogonal dimension.

28. 20. The plasma torch assembly of claim 18, further comprising at least one recirculation path fluidly coupled to the at least one exhaust channel for returning at least a portion of the gas delivered to the plasma zone back to the plasma zone.

29. 30. The plasma torch assembly of claim 28, further comprising a filter coupled to the recirculation path for filtering gas effluent flowing from the plasma zone into the recirculation path prior to returning at least a portion of the gas to the plasma zone.

30. 30. The plasma torch assembly of claim 29, wherein the filter comprises one of an activated carbon filter and a molecular sieve filter.

31. The plasma torch assembly of claim 1 , further comprising at least one cooling channel formed in the wall, the at least one cooling channel configured to receive a coolant.

32. 32. The plasma torch assembly of claim 31, wherein the at least one cooling channel is fluidly isolated from the plasma zone.

33. 33. The plasma torch assembly of claim 32, further comprising a coolant supply in fluid communication with said at least one cooling channel for supplying said coolant to said at least one cooling channel.

34. 2. The plasma torch assembly of claim 1, wherein the seal includes a groove formed in a surface of the wall facing the plasma zone and a sealing element seated in the groove.

35. 34. The plasma torch assembly of claim 33, wherein the sealing element comprises one of an O-ring and a metal seal.

36. The plasma torch assembly of claim 3, wherein the injector has a length in the range of about 5 mm to about 50 mm.

37. The plasma torch assembly of claim 1 , wherein the envelope has an inner diameter within a range of about 5 mm to about 30 mm.

38. The plasma torch assembly of claim 1 , wherein the envelope has a generally cylindrical shape.

39. The plasma torch assembly of claim 1 , wherein the envelope is in the form of a truncated cone.

40. The plasma torch assembly of claim 1 , wherein the envelope has varying cross-sectional dimensions.

41. The plasma torch assembly of claim 1 , wherein the envelope comprises a non-conductive material having a melting point of at least about 300° C.

42. 42. The plasma torch assembly of claim 41, wherein the envelope comprises one of ceramic, glass, alumina, fused silica, and sapphire.

43. 43. The plasma torch assembly of claim 42, wherein the ceramic comprises one of aluminum nitride and aluminum oxynitride.

44. The plasma torch assembly of claim 3, wherein the axial distance of the outlet of the injector to the collector orifice is in the range of about 5 mm to about 60 mm.

45. The plasma torch assembly of claim 3 , wherein the injector is movable relative to the collector orifice.

46. 46. ​​The plasma torch assembly of claim 45, wherein the injector is movable in a plane perpendicular to a longitudinal axis of the torch assembly.

47. 47. The plasma torch assembly of claim 46, wherein the injector is further movable along the longitudinal axis of the torch assembly.

48. 4. The plasma torch assembly of claim 3, wherein the injector has a frusto-conical profile with the injector exit having a smaller cross-sectional area compared to the injector inlet.

49. The plasma torch assembly of claim 1 , further comprising a housing providing a housing in which the envelope is disposed.

50. 50. The plasma torch assembly of claim 49, wherein the housing comprises metal and is configured to protect at least the plasma zone from electromagnetic interference.

51. 50. The plasma torch assembly of claim 49, wherein the housing includes one or more cooling channels for receiving a coolant.

52. The torch assembly is approximately 1×10 ５ The plasma torch assembly of claim 1 , configured to operate at an operating pressure greater than 1000 psi.

53. The operating pressure is about 2×10 ５ Pa ~ approx. 1×10 ６ 53. The plasma torch assembly of claim 52, wherein the plasma torch assembly is in the range of 1000 psi to 1000 psi.

54. 1. A plasma torch assembly comprising: an envelope surrounding a plasma zone in which plasma can be formed; a collection chamber including a wall having at least one collector orifice, the at least one collector orifice providing fluid communication between the plasma zone and the collection chamber; a seal for providing a hermetic connection between the envelope and the wall of the collection chamber around the at least one collector orifice; an injector disposed at least partially within the envelope, the injector extending from an inlet for receiving an injector gas flow to an outlet from which the injector gas exits; and a vortex generator in fluid communication with the plasma zone, the vortex generator configured to deliver a vortex gas flow into an interior of the envelope; The plasma torch assembly, wherein the axial distance between the outlet of the injector and the collector orifice is within a range of about 5 mm to about 60 mm.

55. 55. The plasma torch assembly of claim 54, wherein an outer surface of the injector and an inner surface of the envelope are in direct fluid communication with each other.

56. 55. The plasma torch assembly of claim 54, wherein the envelope has a profile configured to facilitate containment of the plasma within the plasma zone via the vortex gas flow.

57. 55. The plasma torch assembly of claim 54, wherein the envelope has a tapered profile having a decreasing cross-sectional dimension with decreasing distance from the wall.

58. 58. The plasma torch assembly of claim 57, wherein the tapered profile is a frusto-conical profile.

59. 58. The plasma torch assembly of claim 57, wherein the injector has a tapered profile with the injector exit having a smaller cross-sectional area than the injector inlet.

60. 55. The plasma torch assembly of claim 54, further comprising at least one RF coil disposed at least partially around the envelope.

61. 61. The plasma torch assembly of claim 60, further comprising a radio frequency (RF) source in electrical communication with the RF coil for supplying an RF voltage to the RF coil.

62. 62. The plasma torch assembly of claim 61, wherein the RF source is configured to apply an RF voltage to an ignition coil at a frequency in a range of about 900 kHz to about 10 GHz.

63. 55. The plasma torch assembly of claim 54, wherein the axial distance is in the range of about 10 mm to about 40 mm, or in the range of about 20 mm to about 30 mm.

64. 1. A method for generating an inductively coupled plasma in a plasma torch having a torch envelope sealingly coupled to a wall of an analyzer collector, comprising: introducing an inert gas into the interior of the torch envelope; The pressure inside the torch envelope is about 4×10 ４ Pa. The method includes establishing a radio frequency (RF) electromagnetic field within at least a portion of the interior of the torch envelope to ignite a plasma within the gas.

65. The pressure inside the torch envelope is 4×10 ４ 65. The method of claim 64, further comprising increasing the pressure to greater than Pa.

66. The increased pressure is about 1×10 ５ Pa ~ approx. 1×10 ６ The method of claim 65, wherein the temperature is in the range of Pa.

67. 65. The method of claim 64, further comprising utilizing an injector to introduce the sample into the plasma via a carrier gas.

68. 68. The method of claim 67, further comprising adjusting a position of the plasma relative to a longitudinal axis of the torch assembly via adjusting an inclination of the injector relative to the longitudinal axis.

69. 65. The method of claim 64, further comprising adjusting a position of the plasma relative to a longitudinal axis of the plasma torch by adjusting a flow rate of exhaust gas traversing from the plasma zone to one or more exhaust channels disposed in the wall of the collector.

70. 65. The method of claim 64, wherein the axial distance of the outlet of the injector to the collector orifice is in the range of about 5 mm to about 60 mm.

71. 65. The method of claim 64, wherein the injector is movable relative to the sampler orifice.

72. 72. The method of claim 71, wherein the injector is movable in a plane perpendicular to a longitudinal axis of the torch assembly.

73. 72. The method of claim 71, wherein the injector is further movable along the longitudinal axis of the torch assembly.

74. 68. The method of claim 67, wherein the injector has a frusto-conical profile with the injector exit having a smaller cross-sectional area compared to the injector inlet.

75. The torch assembly is approximately 1×10 ５ 65. The method of claim 64, wherein the device is configured to operate at an operating pressure greater than 1000 psi.

76. 76. The method of claim 75, wherein the operating pressure is in the range of about 2 atm to greater than about 10 atm.

77. 1. A plasma torch assembly comprising: an envelope surrounding a plasma zone in which plasma can be formed; a collection chamber including a wall having at least one collector orifice, the at least one collector orifice providing fluid communication between the plasma zone and the collection chamber; a seal for providing a robust, sealed connection between the envelope and the wall of the collection chamber surrounding the at least one collector orifice; an injector disposed at least partially within the envelope, the injector extending from an inlet for receiving a flow of injector gas to an outlet through which the injector gas exits; and a vortex generator in fluid communication with the plasma zone, the vortex generator configured to deliver a vortex gas flow into an interior of the envelope. The plasma torch assembly, wherein the axial distance between the outlet of the injector and the collector orifice is within a range of about 5 mm to about 60 mm.

78. 78. The plasma torch assembly of claim 77, wherein an outer surface of the injector and an inner surface of the envelope are in direct fluid communication with each other.

79. 78. The plasma torch assembly of claim 77, wherein the envelope has a profile configured to facilitate confinement of the plasma within the plasma zone via the vortex gas flow.

80. 78. The plasma torch assembly of claim 77, wherein the envelope has a tapered profile having a decreasing cross-sectional dimension according to a decreasing distance from the wall of the collector.

81. 81. The plasma torch assembly of claim 80, wherein the tapered profile is a frusto-conical profile.

82. 78. The plasma torch assembly of claim 77, wherein the injector has a tapered profile with the injector exit having a smaller cross-sectional area than the injector inlet.

83. 80. The plasma torch assembly of claim 77, further comprising at least one RF coil disposed at least partially around said envelope for igniting a plasma in said plasma zone.

84. 84. The plasma torch assembly of claim 83, further comprising a radio frequency (RF) source in electrical communication with the at least one RF coil for generating an RF electromagnetic field within at least a portion of the plasma zone for igniting the plasma.

85. 85. The plasma torch assembly of claim 84, wherein the RF source is configured to apply an RF voltage to the RF coil at a frequency in a range of about 900 kHz to about 10 GHz.

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