COOLING PLATE FOR ICP-MS

Abstract

Plasma sampling interface (20) for an inductively coupled plasma mass spectrometer (ICP-MS), wherein the plasma sampling interface comprises • a housing (26) comprising an inlet opening (31) for introducing ions from plasma (24) generated by an inductively coupled plasma source (10) into an inner chamber (27) of the housing (26) and an outlet opening (25) for releasing ions from the inner chamber (27); • a sampler (70) with a sampling opening (71), wherein the sampler (70) is mounted on the housing (26), wherein the sampler (70) is arranged in use adjacent to the plasma (24) generated by the inductively coupled plasma source (10) in order to extract ions from the plasma (24) and to release ions extracted as a sample through the inlet opening (31) into the inner chamber (27), wherein the inlet opening (31) is provided in a cooling plate (30) which is integral with the housing (26), wherein the sampler (70) is mounted on the cooling plate (30) in order to at least partially cover the inlet opening (31), characterized in that the cooling plate (30) is made of bronze.

Description

Field of the invention

[0001] The invention relates to an interface for an inductively coupled plasma mass spectrometer (ICP-MS). The invention further relates to a cooling plate for use in inductively coupled plasma mass spectrometers. General state of the art

[0002] Inductively coupled plasma mass spectrometry (ICS-MS) is an analytical technique capable of detecting metals and certain non-metals at very low concentrations, down to 1015 parts per quadrillion (ppq), on unperturbed isotopes with low background activity. The technique involves ionizing the sample to be analyzed with an inductively coupled plasma and then using a mass spectrometer to separate and quantify the resulting ions.

[0003] The sample is typically a liquid solution or suspension introduced as an aerosol in a carrier gas, usually argon. The plasma is generated by ionizing the aerosol in the carrier gas in an electromagnetic coil to produce a high-energy mixture of argon atoms, free electrons, and argon ions.

[0004] The plasma is generated in a plasma torch, which typically has a number of concentric tubes forming corresponding channels and is surrounded at its downstream end by a spiral induction coil. Plasma gas, typically argon, flows into an outer channel of the torch, and an electrical charge is applied to the gas to ionize a portion of the gas. A radio frequency is applied to the torch coil, and the resulting alternating magnetic field causes free electrons to be accelerated, causing further ionization of the gas. This achieves a plasma state with a temperature within the plasma typically in the range of 5,000 to 10,000 K. The sample in the carrier gas flows through a central channel of the torch and enters the plasma, where the extremely high temperature causes atomization and ionization of the sample.

[0005] To form an ion beam from the sample ions in the plasma, the plasma is scanned through an aperture in a vacuum sampling interface. This is accomplished by providing a sampler in the form of a sampling cone (or sampling cone) with a narrow aperture tip, typically with a diameter of approximately 0.5 to 1.5 mm. Downstream of the sampling cone, the plasma within the sampling interface expands as it flows through an evacuated expansion chamber within the interface. A central portion of the expanding plasma passes through a second aperture, provided by a skimmer cone, into a second evacuation chamber with a higher degree of vacuum. Downstream of the skimmer cone are electrostatic lenses that extract ions from the plasma, thereby forming an ion beam.The resulting ion beam is then deflected by one or more ion deflectors, ion lenses, and / or ion guides and / or guided to a mass spectrometer. Sometimes the ion beam passes through a collision or reaction cell to remove potentially interfering ions before passing through the mass spectrometer.

[0006] The plasma is generated in the ICP source at atmospheric pressure. The sampling interface operates at reduced pressure, typically a few mbar. The plasma flow into the interface is thus driven by the pressure difference between the plasma and the expansion chamber within the interface.

[0007] The sampling interface is sensitive to deposits that form on the sampling cone, leading to optical defects, noise, or other artifacts in the obtained mass spectrum. Deposits can form on the sampling cone, particularly near its tip, leading to these artifacts. Blockages can arise either in the sample itself or in components of the sampling interface.

[0008] The conditions at the sample interface in ICP-MS are challenging. Due to the extremely high temperature at the plasma source (up to 10,000 K), the sampler cone must be cooled. This is typically achieved by mounting the sampler cone on a water-cooled plate (cold plate) at the front end of the sampling interface, opposite the ICP source. The sampler cone is typically made of metals that are corrosion-resistant, have high thermal conductivity, and have a high melting point. Typical metals used in the sampler cone are nickel and platinum.

[0009] The cold plate is typically made of copper, which has very high thermal conductivity. To ensure resistance to plasma corrosion, the cold plate is usually coated with a corrosion-resistant coating, such as nickel.

[0010] DE 195 12 793 A1 discloses an ICP-MS system with a conventional plasma interface, comprising a sampling cone and a skimmer cone, wherein the sampling cone is mounted on a water-cooled copper front plate and the skimmer cone is mounted on a water-cooled copper flange.

[0011] JP H11-25903 A also discloses an ICP-MS interface with a sampling cone and a skimmer cone installed on respective water-cooled metal plates.

[0012] JP 2018-146536 also discloses an ICP-MS interface with a sampling cone and a skimmer cone and suggests different materials for the cones, but does not specify materials for mounting plates or any type of cooling.

[0013] Similarly, JP 2003-016989 discloses an ICP-MS interface with a sampling cone and a skimmer cone and suggests various metals and alloys for the cones, but does not describe plates for their mounting or any type of cooling.

[0014] However, the inventors discovered that the nickel coating on the cold plate is susceptible to corrosion by aggressive chemicals. Over time, corrosion of the coating is followed by blistering of the coating, ultimately requiring replacement of the cold plate. Damage to the nickel coating, however, can lead to optical defects, particulate deposition on the sampler cone, and / or contamination by nickel isotopes in the analysis signal. A related problem arises from matrix deposition on the sampler cone, which causes signal drift when analyzing high-matrix samples.

[0015] It would therefore be desirable to provide a sampling interface for ICP-MS that minimizes the effects of corrosion or other deterioration of the cold plate. Brief description

[0016] The present invention addresses the deficiencies described above by providing an improved interface for inductively coupled plasma mass spectrometers (ICP-MS). The invention also provides an improved cold plate for use in sampling interfaces that is resistant to chemical degradation due to the extreme environment provided by the high-temperature plasma from the ICP source.

[0017] Thus, in one aspect, the invention provides a plasma sampling interface for an inductively coupled plasma mass spectrometer (ICP-MS), the plasma sampling interface comprising (i) a housing having an inlet opening for introducing ions from plasma generated by an inductively coupled plasma source into an internal chamber of the housing and an outlet opening for releasing ions from the internal chamber, and (ii) a sampler having a sampling opening, the sampler being mounted on the housing, the sampler being arranged, in use, adjacent to the plasma generated by an inductively coupled plasma source to sample ions from the plasma and to release the sampled ions through the inlet opening into the chamber, the inlet opening being provided in a cold plate integral with the housing, the sampler being mounted on the cold plate so thatthat it at least partially covers the inlet opening, and wherein the cooling plate is made of bronze.,

[0018] Another aspect of the invention relates to a cooling plate for receiving and cooling a plasma sampler in an inductively coupled plasma mass spectrometer (ICP-MS), wherein the cooling plate comprises at least one internal channel for transmitting a coolant through the cooling plate, an opening extending axially through the cooling plate, and a sampler seat portion surrounding this opening for receiving and securing a sampler to the cooling plate, characterized in that the cooling plate is formed from bronze.

[0019] Also disclosed is a method of mass spectrometry using a cold plate as disclosed in this document. Thus, a further aspect relates to a method operating a mass spectrometer sampling interface, the method comprising: (i) generating plasma by means of an inductively coupled plasma (ICP) source; and (ii) sampling the plasma by means of a sampler disposed adjacent to the plasma, the sampler being mounted on an outer surface of a cold plate integral with the housing of a sampling interface, the cold plate being adapted to allow sampled ions to pass through an opening in the cold plate and into a chamber within the sampling interface, and the cold plate being formed of bronze. The cold plate to be used in the method may preferably be a cold plate as disclosed in this document.

[0020] Furthermore, this document discloses a mass spectrometer comprising a cooling plate as disclosed in this document. Also disclosed is a mass spectrometer comprising a plasma sampling interface as described in this document. Such a mass spectrometer can, in particular, be an inductively coupled plasma mass spectrometer (ICP-MS).

[0021] The following description refers to embodiments of the invention. It should be understood that descriptions of embodiments of the cold plate are equally applicable to the cold plate itself, an interface comprising such a cold plate, a mass spectrometer comprising such a cold plate or interface, and methods for operating a mass spectrometry interface comprising such a cold plate.

[0022] The purpose of the plasma interface of an ICP-MS is to efficiently and consistently transfer ions generated in the plasma torch to a downstream mass analyzer. The plasma is generated at atmospheric pressure (about 1 atm), while a mass analyzer typically operates at very high vacuum of only 10 -10 bar. The sampling interface is typically operated at an internal pressure of about 10 -3 bar, while a downstream ion guide is normally operated at a pressure of 10 -5 up to 10 -6bar. The pressure difference between the ICP source and the interface, as well as between the interface and the downstream components of the mass spectrometer, results in a large acceleration of the ions as they enter and pass through the plasma interface. The result is a supersonic ion beam that enters the interface via the sampler (e.g., sampler cone) and exits the interface via a skimmer or skimmer cone.

[0023] The sampler can be provided as a conical structure with an orifice plate, i.e., a sampling cone, usually made of metals with high thermal conductivity and a high melting point, such as Ni deposited on Cu, Al, or Pt. To prevent melting of the cones due to exposure to extreme heat, they are typically mounted on a water-cooled plate, creating a cooling reservoir that cools the sampler and prevents it from melting. State-of-the-art cold plates are typically made of copper, which has a very high thermal conductivity and is therefore suitable for this purpose. To minimize corrosion effects, such cold plates usually have an inert coating, typically of Ni. However, over time, even this coating is subject to degeneration and rust formation due to the harsh plasma conditions.

[0024] The present invention provides a cold plate made of bronze. By making the cold plate made of bronze, two important chemical properties required of such plates are combined: thermal conductivity and chemical resistance. Although the thermal conductivity of bronze is lower than that of copper, it has been found to provide sufficient thermal conductivity for the required cooling of the sampler. Furthermore, bronze is significantly more stable in the harsh conditions of the plasma interface region, as demonstrated by results showing that a bronze cold plate is stable over extended periods when used in ICP-MS analysis (see Example 1 below).

[0025] Bronze is an alloy consisting primarily of copper and typically containing tin as a primary second component. In the present context, bronze is therefore a metal alloy containing copper as the primary component, with tin as the second major component. Bronze may also contain other metals such as arsenic, aluminum, manganese, silicon, nickel, or zinc. The incorporation of metals other than copper into the alloy influences the physicochemical properties of the resulting bronze alloy, affecting properties such as thermal and / or electrical conductivity, stiffness, ductility, melting point, and machinability of the alloy.

[0026] The bronze of the invention may generally consist of about 70% to about 95% copper, about 75% to about 95%, about 80% to about 95%, or about 85% to about 90%, based on the weight of the bronze material. The remainder of the bronze composition may consist of tin, optionally in combination with one or more additional metals. Thus, the remainder of the bronze may comprise 60% or more tin, such as 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more tin.

[0027] The remaining composition of the bronze material may include arsenic, aluminum, manganese, silicon, nickel or zinc, or any combination of two or more of these metals.

[0028] For example, the bronze cooling plate may comprise about 95% copper and about 5% tin, about 94% copper and about 6% tin, about 93% copper and about 7% tin, about 92% copper and about 8% tin, about 91% copper and about 9% tin, about 90% copper and about 10% tin, about 89% copper and about 11% tin, about 88% copper and about 12% tin, about 87% copper and about 13% tin, about 86% copper and about 14% tin, about 85% copper and about 15% tin, about 84% copper and about 16% tin, about 83% copper and about 17% tin, about 82% copper and about 18% tin, about 81% copper and about 19% tin, or about 80% copper and about 20% tin.

[0029] One embodiment comprises bronze containing about 88% copper and about 12% tin by weight of the bronze. Another embodiment comprises about 90% copper and about 10% tin by weight of the bronze. Another embodiment comprises about 86% copper and about 14% tin by weight of the bronze.

[0030] Pure copper has a thermal conductivity of approximately 400 W / mK at room temperature. Bronze has a lower thermal conductivity than pure copper, and its chemical composition is reflected in its thermal conductivity. Accordingly, the bronze according to the invention can have a thermal conductivity in the range of approximately 15 to 200 W / mK, in the range of approximately 20 to 150 W / mK, in the range of approximately 20 to 100 W / mK, in the range of approximately 20 to 80 W / mK, in the range of approximately 20 to 60 W / mK, or in the range of approximately 20 to 50 W / mK. The thermal conductivity thus defined can be the thermal conductivity at or around room temperature, for example in the range of 20°C - 25°C, including at or around 20°C, or at or around 25°C.

[0031] As a result of using bronze as the sole material in the cold plate, the resulting ICP-MS system is more stable in that it can be operated over a long period of time with minimal or no risk of corrosion artifacts, and also in that, due to the higher operating temperature of the sampling cone, the risk of matrix deposition on the sampling cone is lower, which in turn leads to fewer artifacts and more stable operation of the mass spectrometer.

[0032] For example, the physicochemical properties of bronze differ significantly from those of copper, including thermal conductivity and ductility. Furthermore, the addition of tin to copper results in an alloy that is more wear- and corrosion-resistant than pure copper. Bronze is harder and more corrosion-resistant than brass, a copper alloy containing copper and zinc as its main components.

[0033] The cold plate serves as a cooling reservoir. During operation, the sampler is exposed to intense heat from the plasma gas, and this heat is dissipated through the sampler and into the cooling reservoir provided by the plate. The cold plate therefore plays a very important structural role, i.e., for the assembly of the sampler, but above all, a physico-chemical role, acting as a thermal heat sink, keeping the sampler at a relatively low temperature during operation.

[0034] Copper has proven to be a suitable material for the cold plate due to its very high thermal conductivity. A disadvantage of such commonly used cold plates is the relatively low corrosion resistance of copper, which has been compensated for by coating the cold plate with a corrosion-resistant layer, usually made of nickel.

[0035] The increased corrosion resistance of a bronze cooling plate compared to the nickel-plated copper plates currently used represents a major advantage of the invention. Due to its corrosion resistance, the cooling plate does not need to be provided with a corrosion-resistant coating. Thus, the cooling plate according to the invention preferably contains no coating.

[0036] An additional advantage of using bronze in the cold plate is that bronze has a lower thermal conductivity than copper. As a result, the operating temperature at the tip of the sampler cone is expected to be higher when using the bronze cold plate than with state-of-the-art copper plates. A higher operating temperature, while still low enough to prevent damage to the sampler from the hot plasma, is expected to result in less interference from potentially interfering components in the sample being analyzed. This is particularly important for certain high-matrix samples, where matrix components are known to cause redeposition of matrix on the sample cone, which in turn can lead to signal artifacts such as drift and poorer stability when analyzing such samples.

[0037] The sampler is mounted on the cold plate above an inlet port in the plate, so that ions from the plasma entering the sampling interface do so through an opening in the sampler. Typically, this interface is provided by a nozzle at the tip of a conical structure, the sampler cone. During use, the sampler, and thus the cold plate on which the sampler is mounted, faces the ICP source.

[0038] The ICP source is typically placed very close to the sampler or at a distance of approximately 1 cm. As a result, the conditions at the sampler and the cold plate on which the sampler is mounted are quite extreme, partly due to the high temperature of the plasma (5000-10,000 K) and partly due to chemical components of the sample and / or matrix generated by the plasma, which can be corrosive.

[0039] The sampler may typically be in the form of a circular structure, for example, a circular structure with a cone at its center, with a small-diameter nozzle at the apex of the cone, the nozzle defining a sampling nozzle through which ions from the plasma enter the sampling interface. The sampler may be mounted on the cold plate such that the cold plate surrounds at least an outer portion of the sampler. Thus, the sampler may be mounted in a recess on the cold plate that is complementary in shape to the sampler, e.g., in the form of a recess or lip surrounding the opening (entrance port) in the plate.

[0040] The sampler may comprise a flange extending radially from the conical structure. The flange may be adapted to engage an outer surface of the cooling plate surrounding the inlet opening. A securing mechanism may be provided to secure the sampler to the cooling plate via the flange.

[0041] A common problem in ICP-MS is the blockage or corrosion of the interface cones (sampling and skimmer cones), which can result from deterioration of the cones themselves, from matrix components originating from the sample, or from corrosion or deterioration of the interface itself, especially the cold plate.

[0042] The lower thermal conductivity of bronze compared to copper is considered an advantage for certain analyses. It is thought that the slightly reduced thermal conductivity of a bronze cold plate compared to state-of-the-art copper plates results in a higher operating temperature of the sampler, particularly at the sampler cone nozzle, when provided as a conical structure, due to reduced heat dissipation from the sampler. In high-matrix applications, i.e., applications where there is a risk of potentially interfering ions emanating, particularly from a sample matrix, this is expected to result in improved analytical performance because the risk of salt deposition in or around the nozzle in the sampler cone is reduced at higher sampler cone operating temperatures.

[0043] The sampler can be attached to the cold plate using any suitable means. It has been proven advantageous to place a seal, such as a graphite gasket, between the sampler and the cold plate to provide an airtight connection to the plate. This ensures that ions from the plasma gas can only enter the sampling interface via the sampler nozzle.

[0044] In one embodiment, the sampler is attached directly to the cold plate. This can be achieved, for example, by providing a thread on the sampler, such as on the outer periphery of the circular sampler structure (i.e., along its outer periphery) or, alternatively, on an outer periphery of a circular flange portion of the sampler, so that the sampler can be attached to the cold plate via a complementary thread on the circular inlet opening on the plate.

[0045] Alternatively, a threaded securing element may be attached to the cold plate. The purpose of such a securing element is to provide attachment means for the sampler, i.e., to provide means for attaching a sampler to the cold plate. Such a securing element may comprise a circular structure threaded on its inner circumference, the circular threaded opening thus provided being complementary to the sampler when the securing element is attached to the cold plate. The securing element may, for example, be adapted to engage an outer circular portion of the sampler so that the securing element, when attached to the plate, provides means for attaching the sampler to the plate. Accordingly, the sampler may be attached to the cold plate via the securing element.

[0046] The securing element thus provided may be shaped alternatively, in particular it may have different external dimensions, provided that it includes a threaded opening which is complementary to a corresponding threaded portion along the circumference of the sampler, so that the sampler can be attached to the securing element.

[0047] Alternatively, the sampler can be secured to the plate or to a securing element attached to the plate via a securing flange that is attached to the cold plate and simultaneously secures the sampler to the cold plate. The securing flange can be provided so that it meets the outer circumference of the sampler, i.e., an outer portion of the circular sampler. In such an embodiment, the flange is provided as a circular ring structure that is threaded along its outer circumference. The securing flange thus provided can be complementary to a corresponding thread on the cold plate itself or complementary to a securing element attached to the plate. When the flange is screwed onto the cold plate or the securing element, it exerts a radial force on the plate, i.e.a force that is approximately perpendicular to the front of the plate, thereby pressing the sampler onto the plate.

[0048] The cooling plate can be adapted to have a recess extending around the inlet opening in the cooling plate, so that the sampler can be placed within the circular recess thus provided in the plate. A gasket can be placed between the sampler and the plate so that when the sampler is attached to the plate, the resulting connection is airtight.

[0049] Accordingly, in one embodiment, the interface of the invention comprises a securing flange for securing the sampler to the cooling plate and providing an airtight seal therebetween, wherein the securing flange comprises an external thread adapted to engage a complementary thread on the plate to secure the securing flange to the cooling plate and thereby exert force on the sampler to provide a seal between the sampler and the plate.

[0050] The interface may further comprise a securing element, the securing element being adapted to be mounted on the outer surface of the cooling plate and thereby enclosing the inlet opening of the cooling plate, the securing element being further provided with a thread on an inner circular surface thereof to provide a complementary thread for securing the sampler to the cooling plate via the securing flange.

[0051] The interface housing may include a skimmer or skimmer cone through which ions exit the interface. The skimmer may be mounted on an inner surface of the housing, opposite the sampler, and may have an opening for receiving ions generated by the plasma and releasing these ions through the opening. The skimmer preferably covers the exit opening of the interface housing so that ions can exit the interface only through the nozzle in the skimmer cone.

[0052] The interface is pumped to a pressure of approximately 1 mbar by a vacuum pump. The downstream components of the mass spectrometer (including at least one ion guide) typically operate at a pressure of approximately 10 -5bar. Due to the high pressure difference between the ICP source (ambient pressure approximately 1 bar), the interface, and the downstream components, rapid expansion of plasma gas (plasma components within the interface) occurs. The pressure difference and the small nozzles on the sampler and skimmer cones lead to the formation of a supersonic stream of ions that exit the interface and are guided by ion guides and other intermediate components of the instrument into the downstream mass analyzer.

[0053] The cold plate may be cooled, e.g., by internal coolants, to provide a constant temperature heat sink capable of maintaining the sampler at a constant and relatively low temperature. The cold plate may be cooled by a cooling liquid conveyed via internal channels in the plate. Such channels may be machined into the plate or formed by other means known in the art. For example, the channels may be provided as a plurality of straight channels machined into the plate. Where such channels are formed by drilling a plurality of straight, interconnected channels into the plate, a stop may be provided at the end of each of these channels near the periphery of the plate, except for an opening for supplying cooling liquid into the cold plate and an exit for draining liquid from the plate.This allows circulation of the liquid within the cooling plate to be provided.

[0054] Thus, at least one channel may be provided having an inlet opening to allow cooling liquid (e.g., water) to enter the channel and an outlet opening to discharge liquid from the channel. A single channel may be provided for this purpose. There may also be a plurality of interconnected channels within the plate to allow circulation of liquid within the plate. A channel opening and a channel exit may be provided anywhere on the outer portion of the cold plate to provide circulation through the cold plate (i.e., away from the interface). However, it may be preferable to provide such an opening and exit so as to minimize the risk of interference with the analysis and / or the risk of corrosion or other damage from the plasma gas.Therefore, it may be advantageous to place this inlet and outlet on the perimeter of the cold plate side (i.e., on an outer peripheral edge, on a side facing away from the ICP source).

[0055] The above features and additional details of the invention are further described in the following examples, which are intended to further illustrate the invention but are not intended to limit its scope in any way. Brief description of the drawings

[0056] Those skilled in the art will understand that the drawings described below are for illustrative purposes only. The drawings are not intended to limit the scope of the present teachings in any way. Fig. 1 shows an interface area of ​​an ICP-MS device. Fig. 2 shows a cooling plate according to the invention. Fig. Figure 3 shows a front view of an interface comprising a cooling plate according to the invention. Fig. Figure 4 shows a cross-sectional view of a cooling plate and sampler assembly according to the invention. Fig. Figure 5 shows an embodiment in which an internal fluid channel is provided within the cooling plate so that it can be cooled. Description of the different embodiments

[0057] The following describes the embodiments of the invention with reference to the figures. These examples are intended to provide a more thorough understanding of the invention without limiting its scope.

[0058] The following description describes a sequence of steps. Those skilled in the art will appreciate that, unless the context requires, the order of the steps is not critical to the resulting configuration and its effect. Furthermore, those skilled in the art will appreciate that, regardless of the order of the steps, the presence or absence of a time delay between the steps may exist between some or all of the described steps.

[0059] In Fig. Figure 1 shows a plasma interface. The plasma torch 10 consists of three concentric tubes 11, 12, and 13, typically made of quartz. Plasma gas is passed between the outer and middle tubes 11, 12, with an auxiliary gas being supplied between the middle tube 12 and the sample tube 13. A sample is provided in a sample gas through the innermost sample tube 13.

[0060] The plasma torch is centrally located within an RF coil 14, approximately 1-2 cm from the cutting point 20. A high-frequency generator supplies the coil with RF power (typically 750-1500 W). The RF oscillations cause an intense electromagnetic field to be generated at the tip (end) of the torch. As the argon gas flows through the torch, a high-voltage spark is applied to the gas, causing electrons to be removed from argon atoms. These released electrons collide with other argon atoms in the plasma gas, removing even more electrons from the argon atoms. The result is a chain reaction of events that breaks the argon atoms down into argon ions and electrons. This inductive process is maintained by the continuous transfer of RF energy to the torch.

[0061] Sample gas supplied through the innermost tube 13 is introduced into the plasma 24, which has a temperature in the range of 5,000–10,000 K. The result is a series of chemical changes, beginning with the desolvation of the sample (typically provided as an aerosol), followed by gasification and the formation of charged ions through the collision of high-energy electrons and argon ions with ground-state atomic species. The arrow indicates a flow of plasma gas generated in the ICP source toward the plasma interface 20.

[0062] The interface consists of a housing 26 having an internal chamber 27 pumped by a vacuum pump via port 23. Ions from the plasma enter the chamber via a sampler 70, which typically has a conical structure with a narrow opening or nozzle 71 with an internal diameter typically in the range of 0.8–1.2 mm. Within the chamber, the ions sampled from the plasma pass through a second conical structure, referred to as a skimmer 22, which has an opening or nozzle 25 with a diameter typically approximately 0.4–0.8 mm.

[0063] The sampler is mounted on a cooling plate formed integrally with the housing 26 to form at least a portion of the outer surface of the housing 26 facing the plasma torch 10. The cooling plate may cover the entire side 28 of the housing 26 facing the plasma torch 10, or it may cover a portion thereof.

[0064] Downstream of the interface is an ion guide 90, which extracts ions that pass through the interface. The extracted ions are then passed to a mass analyzer (not shown), where the mass-to-charge ratio of the ions is determined.

[0065] The section of the interface facing the ICP torch is located in close proximity to the ICP source (10-20 mm from the outer coil 11). This means that the sampler 70 and the section of the housing on which the sampler is mounted, including the cooling plate, are exposed to the very harsh conditions in the plasma (high temperature and high-energy species in the plasma gas).

[0066] With reference to Fig. 2, a cooling plate 30 is shown which can be mounted on an interface 20 to provide a forward end thereof (i.e., the end facing the plasma torch 10). The cooling plate has an inlet opening 31 which allows the transfer of ions into the internal chamber of the plasma interface 20. The cooling plate can be attached to the plasma interface using fastening means such as screws, using the threaded screw holes 36. The coolant inlet tube 34 and the coolant outlet tube 35 provide means for conveying coolant into internal channels within the cooling plate (not shown) to maintain the main portion of the cooling plate at a relatively constant temperature. Typically, however, there is a temperature gradient within the plate, with the center of the cooling plate, directed towards the sampler (sampler cone), being the hottest.The cooling fluid is typically provided at a temperature of around 20 °C. Consequently, the lower end of the plate's temperature range at the outer peripheral edge of the plate roughly corresponds to the temperature of the cooling fluid. However, in the center, where the cold plate meets the sampler, the cold plate temperature will be significantly higher, up to several hundred degrees Celsius. It should therefore be understood that the thermal conductivity of the plate is very important for its function.

[0067] The inlet opening of the cooling plate is circular. Flanking the opening is a first support section 38 on which a sampler (not shown) can be placed. A second support section 39 is shown, which is located outward and radially from the first support section 38. This second support section 39 is provided for receiving a securing element (not shown) attached to the cooling plate so that the sampler can be hermetically secured to the cooling plate. The securing element, having an annular shape, is attached to the cooling plate 30 by means of screws inserted into the threaded holes 40 on the second support section 39.

[0068] A graphite gasket (not shown) is preferably mounted beneath the sampler to provide an airtight seal between the sampler and the cold plate. The annular gasket is disposed at the first support portion 38 between the cold plate 30 and the sampler. The securing member provides means for securing the sampler to the plate via a securing flange that threads onto the securing member, thereby exerting force on the sampler and the graphite gasket located between the sampler and the cold plate to secure the sampler to the cold plate and provide an airtight connection between the sampler and the plate. This restricts ions from the plasma to enter the sampling interface only via the nozzle 71 on the conical tip of the sampler.

[0069] In Fig. Figure 3 shows a front view of the front end of the plasma sampling interface, facing the adjacent ICP source. A sampler 70 having a generally conical structure is mounted on a cold plate 30 so as to cover the inlet opening of the cold plate. The sampler is secured by the locking flange 60. The circular locking flange is threaded on its outer periphery so that the flange can be screwed into a complementary thread on the locking element 50, which is attached to the cold plate by means of the screws 51. Notches 72 are provided on the locking flange and provide a means for screwing the locking flange 60 into the locking element 50 using a tool (not shown) adapted to fit into the notches 72.While the retaining flange is screwed onto the retaining element, the flange exerts a force axially directed toward the cold plate and sampler, thereby pressing the sampler against the cold plate. A graphite gasket (not shown) between the sampler and the cold plate ensures an airtight seal between the sampler and the cold plate. Panel 80, on which the sampling interface is mounted by means of screws 81, represents the front end of the mass spectrometer housing.

[0070] The cross-sectional view of a cooling plate as shown in Fig. 4, shows the connection and sealing features of the sampler 70 to the cold plate 30 by means of the securing flange 60 and a securing element having a circular shape so that it can be provided as a securing element 50. As can be seen in this view, the cold plate is provided with stepped recesses surrounding the inlet opening in the plate to accommodate the sampler 70, the securing element 50, and the securing flange 60. The sampler 70 thus sits on the innermost of these stepped recesses, with a graphite gasket 95 disposed on the innermost recess where it meets an outer peripheral portion of the sampler 70 to provide a seal between the sampler 70 and the cold plate 30.The retaining element 50 is attached to the cold plate 30 by means of screws (not shown) that thread into threaded holes 52 on the retaining element and the mating threaded holes on the cold plate. The holes 52 are shown extending through the cold plate. However, it should be understood that the holes may extend only partially into the cold plate and may only be open to the retaining element 50. The retaining element is provided with a thread 61 on its peripheral edge surrounding the entry opening in the plate. The retaining flange 60 includes a complementary thread 41 on its outer peripheral edge so that the flange can be screwed onto the retaining element.As the retaining flange is threaded onto the retaining element, it exerts an axial force on the sampler 70, which presses and secures the sampler 70 onto the cooling plate 30, with the gasket 95 providing an airtight seal between the sampler 70 and the cooling plate 30.

[0071] Cooling can be achieved via internal channels that allow the circulation of a coolant within the plate. Fig. Figure 5 shows an embodiment illustrating such a channel. Thus, a cross-sectional view of the cooling plate is shown, in which a series of interconnected channels 32 are provided. The inlet pipe 34 and outlet pipe 35 are connected to the channels 32, thereby enabling the pumping of a coolant through the plate. In this embodiment, the channels 32 are formed by interconnected straight channels that can be drilled into the plate and are closed by plugs 33, except for the portions of the channel 32 connected to the inlet and outlet pipes 34, 35.

[0072] It is understood that this embodiment shows only one possible type of coolant circulation within the plate. Thus, the cooling plate can be cooled by providing alternative shapes and dimensions of the internal channels in the plate. The channels can thus be straight or curved, or contain a combination of curved and straight segments. The channels can further be machined into the cooling plate using all known means of the art. Thus, the channels can be formed by a series of interconnected straight channels, as shown in Fig. 5, in which the channels at the peripheral edge of the cooling plate are closed by plugs, except for the open ends of the resulting interconnected channels, which provide an inlet and an outlet allowing circulation through the channels. Alternatively, the channels may be provided as an integral part of the plate, i.e., they do not extend to the outer peripheral edge of the plate, except for an inlet and an outlet for supplying and releasing liquid. Preferably, the channels extend symmetrically or nearly symmetrically all the way around the cooling plate to provide uniform cooling of the cooling plate in use.

[0073] As can be seen from the above, some advantages of the present invention are: 1. A bronze cooling plate that is extremely resistant to corrosion and other chemical damage. 2. A bronze cooling plate that does not require a coating layer, thus avoiding effects such as chipping, blistering, or other deterioration of the coating. 3. More stable operation of ICP-MS instruments through the use of bronze cooling plates. 4. Increased operating temperature of sample cones mounted on bronze cooling plates, resulting in reduced matrix effects. 5. Reduced fouling effects due to damage to the cooling plate and reduced matrix effects due to increased operating temperature of the sampling cones.

[0074] As used in this document, including the claims, the singular forms of terms should be construed to include the plural form, and vice versa, unless the context clearly indicates otherwise. For example, the singular forms "a" and "the" should be construed to include plural references unless the context clearly indicates otherwise.

[0075] Throughout the specification and claims, the terms “comprise,” “including,” “having,” and “containing,” and their variations, are intended to mean “including, but not limited to,” and are not intended to exclude other components.

[0076] It is understood that changes may be made to the above embodiments of the invention, but these changes still fall within the scope of the invention. Features disclosed in the specification may, unless otherwise stated, be replaced by alternative features serving the same, equivalent, or similar purpose. Thus, unless otherwise stated, each disclosed feature represents an example of a generic series of equivalent or similar features.

[0077] The use of exemplary language such as "for example," "such as," "for example," and the like is intended only to better illustrate the invention and is not intended to be limiting on the scope of the invention unless claimed. All steps described in the specification may be performed in any order or simultaneously, unless the context clearly indicates otherwise.

[0078] All features and / or steps disclosed in the specification may be combined in any combination, except for combinations in which at least some of the features and / or steps are mutually exclusive. In particular, the preferred features of the invention apply to all aspects of the invention and may be used in any combination. Example 1

[0079] The stability of a water-cooled bronze cold plate was tested over time by subjecting the cold plate to prolonged exposure conditions of an ICP source.

[0080] The cooling plate (as in Fig. 2) was made of solid bronze (88% Cu, 12% Sn) and mounted on a sampling interface to provide the front of the interface, which, in use, faces the ICP source. A solid Pt sampling cone was mounted on the plate as shown in Fig. 3 illustrates.

[0081] The interface comprising the water-cooled bronze plate was subjected to a treatment of continuous exposure to plasma at a power of 1250 watts for 14 days, during which time a stream of isopropanol was injected into the plasma.

[0082] At the end of the treatment period, the cooling plate and sampling cone were examined for aging using light microscopy. No visual change in the nozzle size of the sampling cone was observed, indicating that the cooling plate maintained its chemical integrity, at least to the extent that no visible degeneration of the sampling cone occurred.

Claims

[1] Plasma sampling interface (20) for an inductively coupled plasma mass spectrometer (ICP-MS), the plasma sampling interface comprising • a housing (26) comprising an inlet opening (31) for introducing ions from plasma (24) generated by an inductively coupled plasma source (10) into an inner chamber (27) of the housing (26) and an outlet opening (25) for releasing ions from the inner chamber (27); • a sampler (70) having a sampling opening (71), the sampler (70) being mounted on the housing (26), the sampler (70) being arranged, in use, adjacent to the plasma (24) generated by the inductively coupled plasma source (10) to sample ions from the plasma (24) and to release sampled ions through the inlet opening (31) into the inner chamber (27), the inlet opening (31) being provided in a cooling plate (30) which is integral with the housing (26), the sampler (70) being mounted on the cooling plate (30) to at least partially cover the inlet opening (31), characterized by that the cooling plate (30) is made of bronze. [2] The plasma sampling interface (20) of claim 1, wherein the bronze is comprised of about 70% to about 95% copper by weight of the bronze, and wherein at least 80% by weight of the remainder of the bronze is comprised of tin. [3] The plasma sampling interface (20) of any preceding claim, wherein the bronze consists of about 70% to about 95% copper, preferably about 80% to about 95% copper, more preferably about 85% to about 90%, by weight of the bronze, and wherein the remainder of the bronze consists of tin. [4] The plasma sampling interface (20) of any preceding claim, wherein the bronze consists of about 88% copper and about 12% tin by weight of the bronze. [5] A plasma sampling interface (20) according to any preceding claim, wherein the sampler (70) is mounted on an outer surface of the cooling plate (30) which, in use, faces the plasma (24) from an inductively coupled plasma source (10). [6] Plasma sampling interface (20) according to any one of the preceding claims, wherein the cooling plate (30) surrounds at least an outer peripheral portion of the sampler (70). [7] A plasma sampling interface (20) according to any preceding claim, wherein the cooling plate (30) is adapted to face the plasma (24) and is arranged to provide at least a portion of the outer surface of the housing (26) which, during use, faces (24) the plasma generated by an inductively coupled plasma source (10). [8] The plasma sampling interface (20) of any preceding claim, wherein the sampler (70) comprises a conical structure with an open tip for defining the sampling opening (71). [9] The plasma sampling interface (20) of the preceding claim, wherein the sampler (70) comprises a flange extending radially away from the conical structure, the flange being adapted to engage an outer surface of the cooling plate (30) surrounding the inlet opening (31). [10] A plasma sampling interface (20) according to the preceding claim, wherein the flange is externally threaded and wherein the cooling plate (30) comprises a threaded portion on its surface surrounding the inlet opening (31), the threaded portion being adapted to receive the externally threaded flange to secure the flange to the cooling plate. [11] A plasma sampling interface (20) according to any preceding claim, further comprising a securing flange (60) for securing the sampler (70) to the cold plate (30) and providing an airtight seal therebetween, the securing flange (60) comprising an external thread (61) adapted to mate with a complementary thread (41) on the cold plate (30) to secure the securing flange (60) to the cold plate (30) and thereby exert force on the sampler (70) to provide an airtight seal between the sampler (70) and the cold plate (30). [12] The plasma sampling interface (20) of claim 11, further comprising a securing member (50), the securing member (50) being adapted to be mounted on the outer surface of the cooling plate (30) and thereby enclosing the inlet opening (31) of the cooling plate (30), the securing member (50) further being provided with a thread on an inner circular surface thereof to provide a complementary thread for securing the sampler to the cooling plate (30) via the securing flange (50). [13] A plasma sampling interface (20) according to any one of the preceding claims, wherein the bronze has a thermal conductivity in the range of 15 - 200 W / mK. [14] A plasma sampling interface (20) according to any preceding claim, wherein the cooling plate (30) does not comprise any coating or deposit on its outer surface. [15] A plasma sampling interface (20) according to any preceding claim, wherein the housing (26) further comprises a skimmer (22) mounted on an inner surface thereof opposite the sampler (70), the skimmer (22) having an opening for receiving ions from the plasma (24) within the inner chamber and for releasing the sampled ions through the exit opening (25). [16] A plasma sampling interface (20) according to any preceding claim, wherein the cooling plate (30) comprises internal cooling means. [17] A plasma sampling interface (20) according to any preceding claim, wherein the cooling plate (30) comprises at least one internal channel (32) for conducting a coolant flow therethrough and thereby cooling the cooling plate (30). [18] Cooling plate (30) for receiving and cooling a sampler (70) in an inductively coupled plasma mass spectrometer (ICP-MS), wherein the cooling plate (30) comprises at least one internal channel (32) for transmitting a coolant through the cooling plate (30), an opening extending axially through the cooling plate, and a sampler seat portion (38) surrounding the opening for receiving and securing a sampler (70) to the cooling plate (30), characterized by that the cooling plate (30) is made of bronze. [19] Cooling plate (30) according to the preceding claim, wherein the bronze consists of about 70% to about 95% copper, based on the weight of the bronze, and wherein at least 80% by weight of the remainder of the bronze consists of tin. [20] Cooling plate (30) according to one of the two preceding claims, wherein the bronze consists of about 70% to about 95% copper, preferably about 80% to about 95% copper, more preferably about 85% to about 90%, based on the weight of the bronze, and wherein the remainder of the bronze consists of tin. [21] Cooling plate (30) according to one of the three preceding claims, wherein the bronze consists of about 88% copper and about 12% tin, based on the weight of the bronze. [22] A cooling plate (30) according to any one of the preceding four claims, wherein the sampler support portion (38) is adapted to allow the sampler (70) to be mounted on an outer surface of the cooling plate (30) to form a seal (95) between the sampler (70) and the sampler support portion (38) such that plasma ions transmitted from the sampler (70) can pass through the axial opening in the cooling plate (30). [23] Cooling plate (30) according to one of the five preceding claims, wherein the cooling plate (30) is adapted to receive at least one securing element (50) for securing the sampler (70) to the cooling plate (30). [24] The cooling plate (30) according to the preceding claim, wherein the securing element (50) comprises a circular structure adapted to engage an outer peripheral portion of the sampler (70) and thereby secure the sampler (70) to the cooling plate (30). [25] A cooling plate (30) according to any one of the seven preceding claims, wherein the cooling plate (30) is adapted to provide, in use, at least a portion of the outer surface of a plasma interface housing (26) facing the plasma (24) generated by an inductively coupled plasma source (10). [26] A method of operating a mass spectrometer sampling interface (20), the method comprising: • Generating plasma (24) by means of an inductively coupled plasma source (ICP) (10) and • Taking a sample from the plasma (24) by means of a sampler (70) arranged adjacent to the plasma (24), the sampler (70) being mounted on an outer surface of a cooling plate (30) which is integral with the housing (26) of the sampling interface (20), the cooling plate (30) being adapted to allow the sampled ions to flow through an opening in the cooling plate (30) and into a chamber (27) within the sampling interface (20), characterized by that the cooling plate (30) is made of bronze. [27] Method according to the preceding claim, wherein the sampling interface (20) is vacuum pumped. [28] A method according to any one of the preceding claims, wherein the bronze consists of about 70% to about 95% copper by weight of the bronze, and wherein at least 80% by weight of the remainder of the bronze consists of tin. [29] A method according to any one of the three preceding claims, wherein the bronze consists of about 70% to about 95% copper, preferably about 80% to about 95% copper, more preferably about 85% to about 90% copper, based on the weight of the bronze, and wherein the remainder of the bronze consists of tin. [30] A method according to any one of the preceding four claims, wherein the bronze consists of about 88% copper and about 12% tin, based on the weight of the bronze. [31] A method according to any one of the five preceding claims, wherein the sampler (70) is mounted on a support portion (38) on an outer surface of the cooling plate (30) surrounding an axial opening extending through the cooling plate (30), the support portion (38) being adapted to receive the sampler (70) to provide an airtight connection therebetween. [32] A mass spectrometer comprising a plasma sampling interface (20) as recited in any one of claims 1 to 17. [33] A mass spectrometer comprising a cooling plate (30) as recited in any one of claims 18 to 25. [34] A mass spectrometer according to the preceding claim, wherein the mass spectrometer is an inductively coupled plasma mass spectrometer (ICP-MS).

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