Inductively coupled plasma mass spectrometer

Abstract

The sampling interface allows for sampling ions within the mass spectrometer for use in subsequent spectroscopic analysis. The sampling interface comprises an inlet for receiving a fixed amount of particles containing ions for spectroscopic analysis from an ion source; a skimmer located downstream of the inlet, having an opening through which particles from the inlet pass; an extraction lens located downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer; an adjustable voltage source for applying a bias voltage to the extraction lens to generate an electric field in a region at least between the extraction lens and the skimmer; and a controller for controlling the adjustable voltage source to apply a bias voltage to the extraction lens in order to control the reduced electric field in the region directly downstream of the skimmer.

Description

[Technical Field]

[0001] This disclosure relates to improvements in mass spectrometry. More specifically, the present invention relates to sampling interfaces and torches for plasma generation used in mass spectrometers. Specifically, examples of the present invention relate to apparatus and methods for inductively coupled plasma mass spectrometry (ICP-MS). [Background technology]

[0002] A mass spectrometer is a specialized scientific instrument used for the spectroscopic analysis of ionized or charged particles to determine the elemental composition of a sample. Typically, the ionized particles of a sample pass through a mass spectrometer before being received by one or more detectors, where various charged particles are separated based on their respective mass-to-charge ratios.

[0003] Before entering the mass spectrometer, the sample is converted into charged particles or ions, which are then focused and guided through the mass spectrometer to the mass spectrometer. In some types of mass spectrometry, inductively coupled plasma is used to convert the sample into a group of particles, including charged particles or ions. The plasma may be generated, and the introduction of the sample into the plasma may occur at a plasma source (also known as a plasma torch). The flow of particles from the plasma then passes through the mass spectrometer, particularly through a sampling interface. The sampling interface is a part of the mass spectrometer configured to allow ions to be sampled from the generated plasma, and subsequently guide and focus the sampled ions into the mass spectrometer for spectroscopic analysis. Common components of the sampling device include a sampling cone, a skimmer, and an extraction lens, each positioned along the direction of the sample particle flow.

[0004] In mass spectrometers incorporating common sampling interfaces and known conical torches, performance degradation has been observed, particularly during long analytical cycles with high-matrix samples (solutions containing high concentrations of salts, acids, bases, or other chemicals). This degradation manifests as loss of analytical sensitivity (e.g., orders-of-magnet signal decay during an hour-long experiment) and reduced signal reproducibility (where the sample signal appears suppressed in the presence of "high-matrix" components compared to a "clean" sample signal).

[0005] This performance degradation is due to contamination downstream of the conical torch, including the accumulation of high-concentration matrix components in the sampling cone and skimmer. In particular, deposits have been observed around the openings (through which charged particles pass) in both the sampling cone and the skimmer, reducing the diameter of the openings. Figure 1 shows an example of such deposits in skimmer 10, nominally with an opening diameter of 600 μm, after a 4-hour experiment contaminated with high concentrations of salt. It can be seen that the diameter of the skimmer opening 20 has been reduced to approximately 420–450 μm due to the deposits. This reduction in the skimmer opening diameter causes a pressure drop directly downstream of the skimmer assembly, leading to the overall performance degradation described above.

[0006] One known approach to mitigate the loss of analytical sensitivity is to detune specific instrument parameters (e.g., pressure in the region between the sampling cone and the skimmer). Another option is to reduce the gas flow rate through the skimmer orifice to reduce the amount of sediment. However, these methods only partially solve the loss of sensitivity and may further degrade signal reproducibility.

[0007] U.S. Patent No. 9,202,679 describes a sampling interface that allows a bias voltage potential to be applied to a skimmer in order to control the kinetic energy of ions entering the collision region immediately after the skimmer. However, applying a potential to the skimmer opening does not prevent the deposition of salt crystals on the skimmer surface. Furthermore, the voltage that can be applied without disturbing the beam of plasma-generated particles is limited to very small voltages (e.g., a few volts). Therefore, further options for reducing signal degradation are desired.

[0008] Modifications have also been made to the plasma torch. For example, U.S. Patent No. 10212798 describes a torch for generating inductively coupled plasma, comprising torch tubes arranged concentrically around a central injector tube. An annular channel is defined between the torch tubes and the injector tube, and the torch tubes have tapered sections that open towards each end, with a diameter shape such that the annular channel narrows in the middle. To cool the torch, gas can be passed spirally through the annular channel, and the gas flow is accelerated by the narrowed section. However, it is considered beneficial to further improve the torch.

[0009] Therefore, the objective is to provide improved apparatus and methods for inductively coupled plasma mass spectrometry to address these problems. [Overview of the Initiative]

[0010] The first aspect is a sampling interface for use in a mass spectrometer, wherein the sampling interface is arranged in the mass spectrometer to allow sampling of ions for subsequent spectroscopic analysis, and the sampling interface is An inlet for receiving a fixed amount of particles containing ions for the aforementioned spectroscopic analysis from an ion source, A skimmer positioned downstream of the inlet, having an opening through which particles from the inlet pass; An extraction lens positioned downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer, An adjustable voltage source that applies a bias voltage to the extraction lens to generate an electric field in at least the region between the extraction lens and the skimmer, The system includes a controller configured to control the adjustable voltage source to apply a bias voltage to the extraction lens (i.e., to control the bias voltage to the extraction lens) in order to control the reduced electric field in the region directly downstream of the skimmer.

[0011] A second aspect is a method for sampling ions with a mass spectrometer for subsequent spectroscopic analysis, A sampling interface, An inlet for receiving a fixed amount of particles containing ions for the aforementioned spectroscopic analysis from an ion source, A skimmer positioned downstream of the inlet, having an opening through which particles from the inlet pass; An extraction lens positioned downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer, The sampling interface is provided, comprising: an adjustable voltage source that applies a bias voltage to the extraction lens to generate an electric field in at least the region between the extraction lens and the skimmer; The method includes applying a bias voltage to the extraction lens to control the reduced electric field in the region immediately downstream of the skimmer using the adjustable voltage source.

[0012] A third aspect is a torch for generating inductively coupled plasma, A torch tube comprising a support end and an open end, wherein a portion of the open end defines a cavity that at least partially confines the inductively coupled plasma, An injector tube having a bore, the bore extending between an injector inlet end that receives a sample flow and guides it into the bore within the injector tube, and an injector outlet end that conveys the sample flow out of the bore, and the injector tube being arranged to at least partially extend within the torch tube, comprising an injector tube. The diameter of the bore is reduced between a first position and a second position, and is constant or further reduced between the second position and a third position, and the first position is closer to the injector inlet end than the third position in the direction of the sample flow within the bore of the injector tube.

[0013] The present disclosure can be implemented in various ways, some of which are described by way of example only with reference to the accompanying drawings.

Brief Description of the Drawings

[0014] [Figure 1] It is a diagram showing a photograph of deposits generated around the opening through the skimmer of the sampling interface after a 4-hour experiment using an EPA solution (1000 ppm). [Figure 2] It is a schematic diagram showing a sampling interface and a torch arranged as part of an inductively coupled plasma mass spectrometry assembly. [Figure 3] It is a diagram showing both a plot of pressure as a function of time and a plot of the bias voltage applied to the extraction lens over the same period in the region between the skimmer and the extraction lens. [Figure 4] It is a diagram showing a disclosed torch for generating an inductively coupled plasma. Specifically, FIG. 4(a) shows a cross-section in the radial plane of the torch, FIG. 4(b) shows a cross-section in the axial plane of the torch, and FIG. 4(c) shows a perspective view of the torch. [Figure 5] It is a diagram showing a perspective view through the axial plane of a torch with a load coil arranged. [Figure 6] It is a photographic view of an inductively coupled plasma generated by an example of the disclosed torch. [Figure 7] It is a diagram showing a plot of signal intensity over time for calculating the temperature of the plasma generated by the torch. [Figure 8] It is a diagram showing a plot of signal intensity over time when analyzing a calibration solution of 1 ppb using an example of the disclosed torch in an inductively coupled plasma mass spectrometer having a triple quadrupole analyzer. [Figure 9] It is a plot showing the sensitivity limit of measurement in an inductively coupled plasma mass spectrometer having a triple quadrupole analyzer and including an example of the disclosed torch. [Figure 10] It is a diagram showing a plot of signal intensity over time when the voltage applied to the extraction lens is adjusted based on measurable system parameters to maintain a certain reduced electric field (this plot shows good signal reproducibility in a 4-hour experiment using a 1000 ppm EPA solution). [Figure 11] It is a diagram showing a plot of signal intensity over time when the voltage applied to the extraction lens is kept constant (compared with FIG. 10, this plot shows low signal reproducibility in a 4-hour experiment using a 1000 ppm EPA solution). [Figure 12] It is a diagram showing a plot of signal intensity over time showing the signal recovery obtained at the start of a 4-hour experiment using a 1000 ppm EPA solution. [Figure 13] It is a diagram showing a plot of signal intensity over time showing the signal recovery obtained at the end of a 4-hour experiment using a 1000 ppm EPA solution. [Figure 14]This figure shows photographs of the sampling cone and skimmer taken after a 4-hour experiment using 10% seawater (salinity 0.35%, or total salinity 3500 ppm) with an example of the disclosed sampling interface and torch. Figure 14(a) shows the sampling cone before the experiment. Figure 14(b) shows the skimmer before the experiment. Figure 14(c) shows the sampling cone after the experiment. Figure 14(d) shows the skimmer after the experiment. [Figure 15] This figure shows a plot of signal intensity over a longer period of time.

[0015] It will be understood that similar features are given the same reference numerals. The figures are not to scale. [Modes for carrying out the invention]

[0016] This disclosure relates to a sampling interface for use in a mass spectrometer and a method for using the same, as well as a torch for generating inductively coupled plasma for use in an inductively coupled plasma mass spectrometer. The sampling interface and the torch each offer advantages compared to prior art designs, and the combination of these two embodiments yields a superior system overall.

[0017] Figure 2 shows a sampling interface 100 comprising an inlet (or sampling cone) 110, a skimmer 115, and an extraction lens 120. In the specific example in Figure 2, the inlet 110 comprises a sampling cone. The region between the inlet 110 and the skimmer 115 is further referred to as the interface region. The sampling cone and the skimmer 115 each have an opening through which particles or ions can pass. The inlet 110, skimmer 115, and extraction lens 120 are arranged so that particles or ions pass in this order. A variable or adjustable voltage source 125 is arranged to apply a bias voltage to the extraction lens 120. The skimmer 115 may be held at a predetermined voltage, such as 0V (in the specific example in Figure 2, it is held at ground potential). A torch 130 (or conical torch) is positioned near the inlet 110 of the sampling interface 100 so that multiple particles generated by the plasma 135 of the torch 130 pass through the inlet 110.

[0018] During use, a plasma (e.g., inductively coupled) may be generated in the torch 130. A sample may be supplied to the plasma to generate sample ions. Multiple particles generated in the plasma 135, including the sample ions, may pass through the inlet 110 (e.g., through the opening of the sampling cone). The inner diameter of the discharge channel of the injector tube of the plasma torch that generates the plasma (e.g., as described below with reference to Figure 4) may be less than 1 in ratio to the diameter of the opening through the inlet 110, so that most of the particles generated in the plasma pass through the opening of the inlet 110 (usually consisting of a sampling cone) without obstruction. The inlet also serves to form a beam 140 of particles traveling toward the mass spectrometer (not shown) of a mass spectrometer.

[0019] As particles confined in the plasma move downstream, they further pass through the opening of skimmer 115. Skimmer 115 has an interface region (typically in the range of 1.3 to 2 mbar) and a downstream region (typically 2 × 10⁻¹⁶) that includes the extraction ion optics. -3 mbar~5×10-4 This allows for a differential pressure drop between the skimmer and the first extraction lens (pressure in the range of mbar). The electric field between the skimmer and the first extraction lens (hereinafter referred to as the extraction field) and the rapid pressure drop downstream of the skimmer cause the extraction of ionized particles from the plasma. Furthermore, the extraction field is also used to regulate the kinetic energy of the extracted ionized particles and to focus the particle beam.

[0020] In this embodiment, the skimmer 115 is grounded. The skimmer 115 and the sampling cone (which constitutes the inlet 110 in this case) can function as a partial barrier between regions with differential pressure (for example, as part of a differential pump transition from the atmospheric pressure region where plasma 135 is generated in the torch 130 to the low-pressure region of the mass spectrometer. (Note that the mass spectrometer is not shown in Figure 2, but is located in the direction of arrow 145)).

[0021] The extraction lens 120 extracts ionized particles from the plasma and further focuses these ions to form a narrow ion beam that travels toward the mass spectrometer (not shown in Figure 2, but located further downstream of the sampling interface). Efficient extraction of ions from the plasma by the extraction lens 120 increases sampling efficiency and thereby improves analytical sensitivity. Note that the plasma in the interface region between the inlet (e.g., sampler) and the skimmer is electrically neutral, and therefore no extraction occurs there. Consequently, the extraction lens does not affect the interface region.

[0022] During use, a bias voltage is applied to the extraction lens 120 via an adjustable voltage source 125. Applying a bias voltage to the extraction lens 120 (relative to the grounded skimmer 115) generates an electric field in at least a portion of the area between the extraction lens 120 and the skimmer 115. The adjustable voltage source 125 can be used to apply a selected (and possibly user-defined) or predetermined bias voltage.

[0023] An adjustable voltage source 125 is connected to a controller 150, which can adjust or initiate the application of a bias voltage to the extraction lens 120. The controller 150 may be implemented in a computer or be part of a computer system. The controller 150 is configured to receive measured system parameters (or equivalent measured system parameters). The controller 150 can then control (including applying or adjusting) the magnitude of the bias voltage applied to the extraction lens 120 by the adjustable voltage source 125, based on the measured system parameters.

[0024] The system parameters are measurable in "real time" (as numerical values) and may be characteristics that indicate the magnitude of the reduced electric field in the region directly downstream of the skimmer 115 (e.g., proportional, inversely proportional, or in a known relationship). This region may be at least a portion of the chamber between the skimmer 115 and the extraction lens 120, and is a region through which ions passing through the opening of the skimmer 115 must pass.

[0025] The reduced field (also known as the Townsend number) is a standard physical parameter related to the collision probability of ions and neutral particles in the relevant region. The reduced field, or Townsend number, T, may be defined as the ratio of the field in the region E between at least the extraction lens 120 and the skimmer 115 to the number density n in the region immediately downstream of the skimmer 115. Therefore, JPEG2026521073000002.jpg9170

[0026] In some embodiments, the measurable system parameter may be a direct measurement of the electric field or number density. However, in other embodiments, the system parameter may be proportional to either the electric field E or the number density n, or have a known relationship with either of these. In a specific embodiment, the measurable system parameter is the residual pressure (known as the extraction pressure) measured in the region between the skimmer 115 and the extraction lens 120. The pressure may be measured, for example, by a pressure sensor 155 in that region. The pressure sensor 155 may return a measurement of the pressure to the controller 150, which can then determine the bias voltage to apply to the extraction lens 120. It will be understood that the measured pressure is a representation of the number density n and is proportional to the number density.

[0027] When the controller 150 receives a measurement of a system parameter, it may determine the magnitude of the bias voltage applied to the extraction lens 120 based on the measurement. This determination may be based on a predefined relationship or algorithm. The predefined relationship or algorithm may be stored in a storage device 160 that can communicate with the controller 150 and may be read from the storage device, and the determination may be performed by a processor 165 included in the controller 150.

[0028] In a preferred embodiment, the applied bias voltage is determined such that the reduced electric field in the region directly downstream of the skimmer 115 is maintained at a substantially constant value. In other words, a predetermined relationship (between the applied bias and system parameters) may be defined so as to maintain the reduced electric field at a predetermined magnitude. A substantially constant value of the reduced electric field may mean that the reduced electric field is maintained within a range of ±10%, or even ±5% or ±1%, of a predetermined value.

[0029] In a specific embodiment, in measurements using the described apparatus, the extraction field (electric field) E (E = V / d, where V is the difference between the skimmer bias and the voltage applied to the extraction lens 120, and d is the distance between the skimmer 115 and the lens 120) was adjusted to maintain a nearly constant ratio of the extraction field E to the number density n (this ratio is the reduced field, i.e., the so-called Townsend number). As described above, the extraction field is proportional to the bias voltage applied to the extraction lens 120, and in this embodiment, the bias applied to the extraction lens 120 was calculated by the controller 150 based on a measured value of the pressure between the skimmer 115 and the extraction lens 120 (called the extraction pressure). To determine an appropriate applied bias, the controller 150 uses a linear relationship between the measured pressure and the reduced field, and calculates the magnitude of the applied bias to maintain a constant reduced field. The initial setting of the reduced field (e.g., Townsend number) is defined by the optimal extraction field at the initial extraction pressure determined by a clean (uncontaminated) skimmer. Subsequently, the periodically or continuously measured pressure is used in a feedback loop, allowing the controller 150 to repeatedly calculate the bias voltage applied to the extraction lens 120 necessary to maintain a constant reduced electric field.

[0030] In an exemplary measurement where the reduced electric field directly downstream of the skimmer 115 was kept constant, the plot of the applied bias voltage and the measured extraction pressure is shown in Figure 3. It can be seen that the magnitude of the voltage applied to the extraction lens 120 is proportional to the measured extraction pressure. In a specific measurement example from which the data shown in Figure 3 was obtained, the pressure was monitored by a cold cathode gauge type pressure sensor 155 located in the region between the skimmer 115 and the extraction lens 120. Further data obtained from this exemplary measurement are described below.

[0031] The apparatus described can be used in a method for sampling ions within a mass spectrometer for subsequent spectroscopic analysis. The method first includes providing the sampling interface 100, which comprises an inlet 110, a skimmer 115, an extraction lens 120, and an adjustable voltage source 125 for applying a bias voltage to the extraction lens 120, thereby generating an electric field in at least a portion of the area between the extraction lens 120 and the skimmer 115. When in use, some of the particles passing through the sampling interface 100 may be generated by the torch 130 as described above.

[0032] According to the method described above, a bias voltage is applied to the extraction lens 120, and the magnitude of the bias voltage applied to the extraction lens 120 is determined based on measured values ​​of system parameters in order to control the reduced electric field in the region directly downstream of the skimmer. The magnitude of the applied bias voltage may be controlled by the controller 150 as described above. The system parameters are, as described above, any measurable characteristics in the system (e.g., numerically measurable characteristics such as pressure or temperature) that represent the number density in the region directly downstream of the skimmer and therefore have a known relationship (e.g., a proportional relationship) with the magnitude of the reduced electric field in the region directly downstream of the skimmer 115.

[0033] According to the method described above, there may be a further step of measuring the value of a system parameter before the step of applying a bias voltage to the extraction lens 115. This may include measuring the value by a sensor in the system and receiving the measurement (e.g., in the controller 150). In one example, the system parameter is the pressure measured in the region between the skimmer 115 and the extraction lens 120. Once the system parameter is measured, the method may include a further step of determining the magnitude of the bias voltage to be applied to the extraction lens 120 (e.g., by the controller 150). This determination may be based on a predefined relationship between the applied bias voltage and the measurement of the system parameter. In some embodiments, the magnitude of the applied bias voltage may be determined (e.g., via a predefined relationship) to maintain the reduced electric field at a substantially constant value.

[0034] The torch 130 (or conical torch) used to generate the plasma 135, as shown in Figure 2, from which multiple particles pass through the sampling interface 100, may be any known type of torch or conical torch that satisfies the specific constraints described below. However, the inventors of this disclosure have found specific improvements to known conical torch designs that, when combined with the sampling interface described above, provide concrete advantages. In particular, improvements to the torch 130, as described below, may result in higher temperatures and a more focused beam of particles passing through the sampling interface 100. This consequently allows for a reduction or removal of material deposits at the inlet 110 and the maintenance of a constant interface pressure between the inlet 110 and the skimmer 115. On the other hand, if the interface pressure monotonically decreases due to contamination of the inlet 110, changes in supersonic gas expansion into the interface region may occur, accompanied by a monotonically increasing Mach disk position. This process may adversely affect the analytical sensitivity of the instrument and may be an additional factor causing a pressure drop in the extraction region. As a result, a more complex approach may be required to elucidate the pressure drop resulting from the combined contamination of both the sampling cone and the skimmer. Therefore, maintaining a constant interface pressure (pressure in the region between the sampling interface inlet and the skimmer) allows for better control of the reduced electric field downstream of the skimmer. By using the disclosed torch, the charged particle flow generated by the plasma in the torch can pass through the inlet to the sampling interface without obstruction, making it possible to maintain the interface pressure at a nearly constant value.

[0035] The improved torch 230 (or improved conical torch) is shown in Figure 4. Specifically, Figure 4(a) shows a cross-section of the torch 230 in the radial plane, Figure 4(b) shows a cross-section of the torch 230 in the axial plane, and Figure 4(c) shows a perspective view of the torch 230.

[0036] Torch 230 is for generating inductively coupled plasma, and in particular for generating particles (including sample ions) to be supplied to the sampling interface of a mass spectrometer. Torch 230 comprises a torch tube 410 and an injector tube 415, the injector tube 415 extending within the cavity (or bore) of the torch tube 410, and the torch tube 410 is radially positioned around and outside the injector tube 415. In most cases, the torch tube 410 and the injector tube 415 are arranged concentrically. The central axes of tubes 410 and 415 are aligned and extend longitudinally (the longitudinal dimension is greater than their respective radii). The axes passing through tubes 410 and 415 are substantially linear. The positioning of the injector tube 415 within the torch tube 410 defines a channel 420 between the outer surface of the injector tube 415 and the inner surface of the torch tube 410 (i.e., the bore surface). This channel 420 can be used to pass gases such as a cooling gas and / or a confinement gas through in order to cool the torch tube 410 and confine the plasma generated in the torch 230 when the torch is in use.

[0037] The torch tube 410 and the injector tube 415 may each have one end connected to a support device (a support device 425 shown only in Figures 4(a), 4(c), and 5). The support device holds the injector tube 415 and the torch tube 410 in place relative to each other. One end of the torch tube 410 is connected to the support device and is called the support end 430, and the opposite end of the torch tube 410 is called the open end 435. The open end 435 of the torch tube 410 is open in the sense that it is neither capped nor closed. The end of the injector tube 415 closest to the support end 430 is called the injector inlet end 440 because it is the end into which the sample is injected when the torch is used into the bore 450 of the injector tube 415. The opposite end of the injector tube 415 is called the injector outlet end 445 because it is the end of the injector tube 415 from which the sample is discharged when the torch is used.

[0038] The bore 450 (a cavity for transporting the sample as it passes through the tube) that runs through the center of the injector tube 415 is composed of sections of different diameters. Generally, the end of the bore 450 closest to the injector inlet end 440 has a larger diameter than the section of the bore 450 closest to the injector outlet end 445. The bore 450 may be tapered so that its diameter decreases in certain sections along its axial extension. The final section 455 of the bore 450 that extends to terminate at the injector outlet end 445 has a substantially constant diameter, which is generally a narrower diameter that follows the tapered section.

[0039] In a specific embodiment, the diameter of the bore 450 within the injector tube 415 is larger at the first position 460 than at the second position 465. Furthermore, the diameter of the bore 450 at the second position 465 is equal to or larger than that at the third position 470. The first position 460 is closer to the injector inlet end 440 than the third position 470, and the second position 465 is located between the first position 460 and the third position 470 in the direction of extension of the bore 450 within the injector tube 415. In other words, the first position 460, the second position 465, and the third position 470 are arranged in this order in the direction in which the sample passes through the injector tube 415 from the injector inlet end 440 to the injector outlet end 445. In the embodiment shown in Figure 4, the bore 450 of the injector tube 415 extending from the injector inlet end 440 to the first position 460 has a first diameter that is constant in this first section 475. The bore 450 of the injector tube 415 extending from the first position 460 to the second position 465 is tapered or gradually decreases in diameter, forming a second conical (or frustoconical) section 480. Finally, the bore 450 of the injector tube 410 extending from the second position 465 to the third position 470 (the injector outlet end 470 in the embodiment of Figure 4) has a second diameter that is constant in this third section 455.

[0040] The first diameter is larger than the second diameter. In the specific example shown in Figure 4, the diameter is approximately 3.9 mm in the first section 475 and the second diameter is approximately 1.0 mm in the third section 455, and these are constant over the respective lengths of each section 475 and 455. More generally, the first diameter may be at least twice, at least three times, or at least four times the second diameter. The constant diameter in the third section 455 means that the diameter at the second position 465 does not exceed 110% of the diameter at the third position 470, ideally not exceeding 105% or 101%. In specific embodiments, the diameter at the second position 465 is equal to the diameter at the third position 470. The distance between the second position 465 and the third position 470 is typically at least five times the diameter of the bore at the second position 465, or at least ten times the diameter at the second position 465.

[0041] Several advantages are obtained by providing an injector tube 415 with a reduced diameter structure in which the reduced diameter or tapered portion 480 is spaced away from the injector outlet end 445. In particular, the sample (e.g., atomized gas) entering the injector tube 415 through the larger bore diameter region 475 contracts as it passes through the narrowing bore diameter region 480, resulting in accelerated gas flow that converges into a narrower particle flow at the outlet of the injector outlet end 445. The linear section of the torch extending near the injector outlet end 445, the bore diameter of the injector tube that narrows in the flow direction, and the low cooling gas flow of the torch allow RF power to be coupled to the plasma more efficiently, improving energy transfer to the central plasma channel. As a result, higher plasma temperatures are measured when using the torch 230 with the injector tube 415 compared to many known torch configurations.

[0042] In the example shown in Figure 4, the injector tube 415 is positioned to extend only a portion of the length of the bore of the torch tube 410. In particular, the injector outlet end 445 is located inside the torch tube 410, spaced apart from the open end 435 of the torch tube 410. This creates a portion at the open end 435 of the torch tube 410 where the injector tube 415 does not extend through the bore, resulting in the formation of a cylindrical or partially conical cavity 485 at the open end 435 of the torch tube 410. This cavity 485 is hereby referred to as the housing section 490 of the torch tube 410. When the torch 230 is in use, at least a portion of the plasma may be generated within the housing section 490.

[0043] The torch tube 410 (or at least the bore of the torch tube 410) may include conical (frustoconical) or tapered sections. In particular, the bore of the torch tube 410 widens towards the open end 435 compared to the preceding section near the support end 430. In the embodiment shown in Figure 4, the bore of the torch tube 410 has various sections positioned between the support end 430 and the open end 435. These sections include: a) a first section 510 having a constant first diameter along the region near the support end 430; b) a conical (frustoconical) section 505 whose bore diameter narrows to a second diameter; c) a third section 500 having a constant diameter (second diameter); d) a conical (frustoconical) fourth section 495 that partially corresponds to the injector outlet end 445 and widens to a third diameter; and e) a fifth section 490 that includes the housing section and has a constant diameter (third diameter). It will be understood that the second diameter is smaller than the first and third diameters and forms the narrower third section 500 of the bore of the torch tube 410. The first and third diameters may be equal or different. In the specific embodiment of Figure 4, the first diameter is larger than the third diameter, but in some embodiments, the first and third diameters may be equal or different. Advantageously, the reduced diameter of the third section 500 reduces the dimensions of the channel 420 between the inner wall of the torch tube 410 and the outer wall of the injector tube 415, thereby accelerating the axial velocity of the gas flow through the channel 420. When using the torch 230, greater acceleration of the gas (sometimes referred to as the confinement gas) results in better confinement of the generated plasma and greater cooling force to avoid damage or melting of the torch tube 410.

[0044] The outer diameter of the injector tube 415 may be constant along its entire length. Alternatively, as shown in Figure 4, the outer diameter of the injector tube 415 may be tapered and widened just before reaching the injector outlet end 445. As described above, the widened tapered (or conical) portion 515 of the outer diameter of the injector tube 415 may be at least partially aligned with the widened conical portion in the fourth section 495 of the torch tube 410. In particular, the widened conical (or frustoconical) region 515 on the outer surface of the injector tube 415 may be aligned with the bore of the torch tube 410, such that the radial spacing in the widened region 515 is equal to the radial spacing in the narrowed third section 500 of the bore of the torch tube. In other words, the channel defined between the outer surface of the injector tube 415 and the inner surface of the torch tube 410 has a constant radius width throughout the region adjacent to the narrowed third section 500 of the torch tube 410 and the enlarged conical section 515 of the injector tube 415. As mentioned above, the conical section 515 on the outer surface of the injector tube 415 maintains the high flow velocity of the already accelerated gas passing through the narrow channel 420 defined between the outer surface of the injector tube 415 and the inner surface of the torch tube 410, and also guides the flow of confined gas through the containment section of the torch tube 410. The distance between the enlarged conical section 515 on the outer surface of the injector tube 415 and the inner surface of the torch tube 410 can be selected so that the axial velocity of the gas flowing from the support end 430 of the torch tube 410 toward the open end 435 of the torch tube 410 is sufficiently accelerated, and the plasma is well confined.

[0045] As shown in Figure 5, the torch 230 further comprises a load coil 550. The load coil 550 carries a high-power, high-frequency current and, together with the other components of the torch, generates a strong magnetic field for producing a more stable, high-temperature plasma. The load coil 550 is wound around the outer surface of the torch tube 410 so as to align with a portion of the housing section 490. The load coil 550 extends spirally around the axis of the torch tube 410, from a first point 555 (near the support end 430) to a second point 560 (near the open end 435). In the embodiment of Figure 5, the first point 555 is axially away from the injector outlet end 445. Specifically, the gap 570 is 1 mm or more. The second point 560 of the load coil 550 is also axially away from the open end 435 of the torch tube 410 (in the embodiment of Figure 5, the gap 575 is 3 mm or more). Preferably, a specified gap 570 between the injector outlet end 445 and the first point 555 of the load coil 550 prevents or mitigates plasma extinction and torch melting due to high-temperature plasma. Furthermore, the housing section 490 of the torch tube 410 extends beyond the load coil 550 (only by a specified gap 575 between the second point 560 of the load coil 550 and the open end 435 of the torch tube 410), allowing for a further increase in plasma temperature and better collimation of particle flow. It will be understood that such an arrangement of the load coil 550 with the aforementioned gap can be advantageously applied to the torch configuration even without the specific configuration of the injector tube 415 described above and shown in Figures 4 and 5. Thus, the arrangement of the load coil 550 can provide technical advantages independent of the other features of the described torch 230, while also acting complementary to the advantages provided by the other features to further improve the overall performance of the apparatus.

[0046] Advantageously, the conical plasma torch 230 shown in Figures 4 and 5 can be used to generate a higher temperature and more confined plasma than conventional configurations. Specifically, the described torch 230 generates an ion temperature exceeding 10,000 K and a fine flow of charged particles confined in a beam less than 1 mm in diameter. These aspects reduce the deposition of high-matrix contaminants at each element of the sampling interface. Such deposition can cause destabilization of the reduced electric field downstream of the skimmer and the resulting degradation of measurement performance.

[0047] Furthermore, the described torch 230 can be used in conjunction with, or configured as part of, the described sampling interface 100 and can be used to improve the overall system for inductively coupled plasma mass spectrometry. More specifically, when the torch 230 is used to form plasma 600, a fluid passes through the bore of the injector tube 415 from the injector inlet end 440 toward the injector outlet end 445. The fluid may contain a liquid or a gas. Once it passes through the injector outlet end 445 and enters the region of the housing section 490 of the torch tube 415, plasma can be generated or ignited. A liquid or gaseous sample for analysis may be introduced into the fluid via the injector tube 415 and injected into the generated plasma. Reducing the bore diameter of the injector tube 415 increases the acceleration of the fluid passing through the tube, resulting in a rise in the temperature of the generated plasma. The reduced bore diameter, combined with an extended section of the reduced bore positioned directly in front of the injector outlet end, also contributes to generating a more collimated beam. Overall, the plasma temperature is determined by the coupling of RF power and cooling gas flow. The plasma temperature in the central channel (the part closest to the center of the flow) is lower than that in the peripheral region (the part extending radially outward from the center of the flow). In a desirable system, efficient energy transfer is achieved from the peripheral plasma near the torch walls to the central channel.

[0048] Simultaneously, a gas (referred to here as the confinement gas) passes through a channel 420 between the outer surface of the injector tube 415 and the inner surface of the torch tube 410. This gas flows through the channel 420, creating a ring of confinement gas around the plasma generated within the containment section 490 of the torch tube 410. The confinement gas serves to better confine the plasma (to narrow the particle beam emitted from the plasma) and also to cool the torch tube 410 and the injector tube 415. The tapered section 515, which widens the diameter of the outer surface of the injector tube 415, along with the tapered section 495, which widens the bore of the torch tube 410 toward the containment section 490, plays a role in increasing the acceleration of the confinement gas through the defined channel 420.

[0049] Particles (including ions or neutral particles) are drawn into the plasma and travel toward the sampling interface 100, and then pass through the sampling interface 100 toward the mass spectrometer. The described torch 230 features a higher temperature plasma than conventional devices and generates a faster, narrower beam of particles that passes through the sampling interface inlet 110 and skimmer 115. This suppresses deposits at the openings of the inlet 110 and skimmer 115, resulting in smaller deviations in the reduced field (or Townsend number) in the region directly downstream of the skimmer 115 during long-duration experiments. Furthermore, the deviation in the reduced field can be adequately suppressed by the bias voltage applied to the extraction lens 120 of the sampling interface 100, as described above, and this technique itself also has the effect of further reducing deposits in the skimmer.

[0050] The relevant feature of the described torch is the ratio of the inner diameter of the injector tube at the injector outlet end to the diameter of the opening in the inlet 110 (or sampling cone) at the sampling interface 100. This ratio should be kept below 1, so that particles passing through the central channel of the inductively coupled plasma propagate through the sampling cone without obstruction. This feature prevents contamination (i.e., deposition) at the opening of the inlet 110 and maintains a constant pressure in the interface region between the inlet and the skimmer during long-term experiments with high-matrix samples. By preventing contamination of the inlet, the reproducibility of supersonic gas expansion into the interface region is ensured, enabling ion extraction from the plasma that depends on only one independent variable, such as the extraction pressure after passing through the skimmer opening 115. This is useful because, as mentioned above, the degradation of instrument performance due to contamination of the skimmer 115 can be addressed by maintaining a constant reduced electric field.

[0051] Figure 6 is a photograph showing the operation of a torch 230 in which inductively coupled plasma 600 is generated in the conical torch housing section 490. In this photograph, the load coil 550 and the torch tube 410 are visible. Multiple particles emitted from the plasma 600 can be seen moving towards and passing through the opening of the inlet 110 of the sampling interface 100 (this inlet is the sampling cone shown in Figure 6). In the specific measurements shown in Figure 6, the bore diameter of the injector outlet end is 1 mm (the injector tube itself is not visible). Once exiting the injector tube, the finely dispersed aerosol particles are atomized and sent to the high-temperature plasma at a nebulizer flow rate of 0.9 milliliters per minute. The load coil 550 is located immediately downstream of the injector outlet end and simultaneously upstream of the open end of the torch tube 410, thus playing a role in reducing plasma loss and torch melting. A portion of the housing section 490 of the torch tube 410 extends beyond the load coil 550, which allows for a further increase in plasma temperature and better collimation of the particle flow from there.

[0052] Figures 7–15 show various measurements characterizing the described sampling interface 100 and torch 230. Each measurement is performed on plasma generated with a 1 ppb calibration solution using the apparatus according to this disclosure. More specifically, Figures 7, 8, and 9 illustrate the specific advantages obtained by the disclosed torch 230, and Figures 10–15 show that the use of the disclosed sampling interface 100 reduces measurement degradation. The torch 230 and sampling interface reduce deposition and contamination in the inlet (sampling cone) and skimmer, thereby mitigating the resulting adverse effects on measurement performance.

[0053] Figure 7 shows the time-dependent measurement results of the signal intensity, and the plasma temperature of the conical torch can be determined as the ratio of the signals of the dual-charged Ba and U to their single-charged counterparts. Figure 7 shows that the achieved plasma temperature exceeds 10,000 K compared to 7,500 K for a conventional facel torch.

[0054] Figure 8 shows the signal intensity over time when analyzing a 1 ppb calibration solution using the disclosed conical torch in an inductively coupled plasma mass spectrometer equipped with a triple quadrupole analyzer. Here, the sampling cone opening is 1.1 mm and the skimmer opening diameter is 0.5 mm. Figure 9 shows the detection limits in the same inductively coupled plasma mass spectrometer equipped with a triple quadrupole analyzer. In the analysis of a high matrix content solution (US Environmental Protection Agency (EPA) solution, total matrix concentration 1000 ppm), contamination of the 1.1 mm aperture sampling cone was confirmed to be significantly reduced during a 4-hour experiment by using the disclosed torch 230. This was demonstrated by both the stable pressure measured in the region between the sampling cone and the skimmer, and the visual analysis of the sampling cone under a microscope (e.g., shown in the photograph in Figure 14, which will be further detailed below).

[0055] To further improve signal recovery from high-matrix samples, it was found that the open end 435 of the torch tube 410 needs to be positioned retracted along the z-axis, i.e., the interface axis, from the inlet 110 (i.e., the inlet of the sampling cone). The optimal distance between the torch tube 410 and the inlet 110 was found to be 8 mm, although this distance may be in the range of, for example, 5 mm to 10 mm. It has been noted that it is not necessary to further increase the flow rate of the nebulizer (confinement gas) to compensate for the distance between the conical torch and the sampling cone, indicating that the radial confinement of the particle flow has a diameter of less than 1 mm. As mentioned above, this radial confinement, which is larger than that of many conventional conical torches, is due to the gradually decreasing bore of the injector tube 415, the torch tube 410 protruding beyond the injector outlet end 445 (e.g., in the housing section 490), and the relative positioning of the load coil 550 around the housing section 490. By increasing the retraction distance (spacing) of the torch 230 relative to the inlet 110 of the sampling interface 100, it becomes possible to increase the residence time of the analyte in the higher temperature plasma. This promotes better ionization efficiency and improved signal recovery.

[0056] Figures 10, 11, 12, and 13 illustrate the performance of the inductively coupled plasma-triple quadrupole mass spectrometry measurement, which was performed using a sampling interface 100 including the disclosed torch 230. The experiment was performed using an EPA solution (matrix concentration 1000 ppm, with Na, Ca, K, Mg, and Fe all at 200 ppm).

[0057] Figure 10 shows the measurements taken over a 4-hour experiment. 9 Be, 89 Y, 115 In and 238It shows the signal reproducibility regarding the signal intensity of U. Here, the extraction electric field generated by the bias voltage applied to the extraction lens 120 was adjusted during measurement based on monitoring the pressure between the skimmer 115 and the extraction lens 120, and the reduction electric field immediately downstream of the skimmer 115 was maintained constant. Despite obvious deposits being seen on the skimmer after the experiment, no significant decrease in signal intensity was observed. For comparison, FIG. 11 shows the measured over a 4-hour experiment when the extraction electric field was kept constant (i.e., when the pressure-dependent adjustment of the extraction electric field was not performed). 9 Be 89 Y 115 In and 238 It shows the signal reproducibility regarding the signal intensity of U. Under these operating parameters, a gradual decrease in the ion signal was observed.

[0058] FIGS. 12 and 13 show the recovery efficiency of the monitored element before and after a 4-hour experiment using a high-concentration sample used to obtain the results shown in FIG. 10 (in other words, during the period when the bias applied to the extraction lens was adjusted to provide a constant reduction electric field). FIG. 12 shows the signal recovery obtained at the start of the 4-hour experiment, and FIG. 13 shows the signal recovery obtained at the end of the 4-hour experiment. As shown in the data, the signal recovery was found to be in the range from 80% of U at the start of the 4-hour experiment to 120% at the end of the 4-hour experiment. 238 U was found to be in the range from 80% to 120% at the end of the 4-hour experiment.

[0059] Figure 14 shows images of the sampling cone and skimmer taken before and after a 4-hour experiment using the high-concentration sample used to obtain the results shown in Figure 10. Images of the sampling cone before (Figure 14(a)) and after (Figure 14(b)), and of the skimmer before (Figure 14(c)) and after (Figure 14(d)), show that the initial inner diameters of the sampling cone and skimmer were 1.1 mm and 0.6 mm, respectively, and remained substantially unchanged. During the 4-hour experiment, the total pressure-dependent adjustment of the bias voltage applied to the extraction lens was approximately 35 V (-330 V to -295 V). The new configuration of the Torch 230 and the technique of applying the bias voltage to the extraction lens of the sampling interface reduce deposition and contamination at the apertures of the sampling cone and skimmer, maintaining overall measurement quality.

[0060] Figure 15 shows a plot of signal intensity over a longer measurement period (specifically, 10 ppb spiked in 10% seawater). 9 Be, 1 ppb 89 Y, 1 ppb 115 In and 1 ppb 238 (Measurement of U). The plot shows the data recording over the entire 4-hour period in which the extraction field was adjusted in a data-dependent manner (in other words, the bias applied to the extraction lens was adjusted based on the pressure reading measured in the region between the skimmer and the extraction lens). As shown in Figure 14, the overall adjustment of the applied bias at the extraction lens was approximately 35V (-330V to -295V). Similar to the experiment using the EPA matrix, no signal degradation was observed throughout the entire 4-hour experiment.

[0061] Embodiments relating to this disclosure are described with reference to specific types of devices and applications (particularly inductively coupled plasma mass spectrometry), and such embodiments have specific advantages in such cases; however, as stated herein, the approaches relating to this disclosure are also applicable to other types of devices and / or applications. Certain features may be omitted or substituted, for example, as shown herein. Each feature disclosed herein may be replaced by an alternative feature that serves the same, equivalent, or similar purpose unless otherwise specified. Thus, unless otherwise specified, each feature disclosed is merely an example of a general set of equivalent or similar features.

[0062] In this detailed description of various embodiments, many specific details are included for illustrative purposes to provide an overall understanding of the disclosed embodiments. However, those skilled in the art will understand that these various embodiments are implementable with or without specific details. Furthermore, those skilled in the art will readily understand that the specific order in which the methods are presented and performed is illustrative, and that any changes in order may still remain within the scope of the various embodiments disclosed herein. For example, the array of switchable values ​​at the "first" or "second" position of the multi-directional valve is arbitrary.

[0063] Where used herein, including in the claims, the singular form of a term is interpreted as including the plural form unless otherwise specified in the context. For example, where otherwise specified in the claims, the singular demonstrative pronouns in this specification, such as "a" or "an," mean "one or more." Throughout the specification and claims of this disclosure, words such as "comprise," "including," "having," and "contain," as well as variations of these words, such as "comprising" and "comprises," or similar, mean "including, but not limited to," and are not intended to exclude other components. Furthermore, the use of "or" is inclusive, and the expression "A or B" holds if "A" is true, if "B" is true, or if both "A" and "B" are true.

[0064] Any use of any example or illustrative language provided herein (such as "for instance," "such as," "for example," and similar language) is intended merely to better illustrate the invention and, unless specifically claimed, does not imply any limitation to the scope of this disclosure. No language herein should be construed as indicating any element not claimed to be essential to the practice of this disclosure.

[0065] The terms “first” and “second” may be reversed without altering the scope of the invention. That is, what is called a “first” element or position may be called a “second” element or position, and what is called a “second” element or position may be considered a “first” element or position.

[0066] Any steps described herein may be performed in any order or concurrently, unless otherwise stated or contextually required. Furthermore, if a step is described as being performed after another step, this does not preclude the execution of an intervening step.

[0067] Furthermore, unless otherwise implicitly or expressly understood or stated, it is understood that any given component or embodiment described herein may be used individually or in combination with any of the candidates or substitutes listed for that component in general use. Such lists of candidates or options are understood to be illustrative and not limiting unless otherwise implicitly or expressly understood or stated.

[0068] All documents and similar materials cited in this application, including but not limited to patents, patent applications, articles, books, papers, and internet web pages, are expressly incorporated by reference in their entirety for any purpose. Unless otherwise stated, all technical and scientific terms used herein are to be understood in common by those skilled in the art to which the various embodiments described herein belong.

[0069] As described in the specific embodiments above, this disclosure relates to a sampling interface for use in a mass spectrometer, a method for using the same, and a torch for generating inductively coupled plasma. The sampling interface may include the aforementioned torch. In particular, the inventors of this disclosure have recognized that contamination of instrument elements (such as skimmers and sampling cones) located downstream of the torch from which the plasma is generated can lead to degradation of instrument performance. This causes a change in the ratio of ion number to neutral particle number in the region downstream of the skimmer of the instrument. The inventors have further recognized that the reduced field can serve as an indicator of the effect of contamination, and that the problem of instrument performance degradation can be improved by providing an instrument that can maintain a constant reduced field (i.e., expressed as Townsend number) downstream of the skimmer.

[0070] The inventors identified two complementary mechanisms that can maintain a constant reduced electric field. These mechanisms are: a) to adequately control the electric field downstream of the skimmer to account for changes in number density and to counteract the changes in number density with changes in the electric field, thereby achieving the desired constant reduced electric field; and b) to reduce deposition or contamination at the inlet of the sampling interface and / or the opening of the skimmer. The reduction of deposition or contamination at the skimmer orifice itself can be achieved by i) using a high-temperature plasma to generate sample ions, and ii) improving the confinement of the high-temperature plasma in the torch to more concentrate the particle flow passing through the inlet of the sampling interface and the orifice of the skimmer.

[0071] By better focusing the flow of charged particles, the charged particles can pass through the skimmer without obstruction, thereby avoiding a significant increase in pressure in the region between the sampling interface inlet and the skimmer. The resulting nearly constant pressure in the interface region between the inlet and the skimmer facilitates the control of the reduced electric field in the region downstream of the skimmer. Therefore, by using a torch that achieves the above effects (i) and (ii) in combination with the sampling interface described above, a system with superior overall performance can be obtained. In other words, the inventors recognized physical phenomena that cause known problems related to equipment performance degradation and further identified specific equipment operating parameters and characteristics that can avoid or reduce the occurrence of such physical phenomena. This improves overall performance issues.

[0072] This disclosure outlines a sampling interface used to implement the mechanism described above. In particular, the sampling interface itself, having an adjustable voltage source for applying a bias voltage to the extraction lens, can be used to achieve mechanism (a) by sufficiently changing the electric field, without disturbing the electric field upstream of the apparatus which could affect the plasma generated by the torch. The torch described in this disclosure can be used to achieve mechanism (b) and the associated benefits of (i) and (ii). The described sampling interface also plays an auxiliary role to mechanism (b), as evidenced by the fact that applying a bias to the extraction lens (rather than other factors) has been shown to contribute to reducing deposition in the skimmer. Although the described sampling apparatus and torch each have their own individual and independent advantages, a unique improvement to avoid overall performance degradation of the apparatus is obtained by combining the described sampling interface and torch.

[0073] In the first embodiment described, a sampling interface for use in a mass spectrometer, wherein the sampling interface is arranged in the mass spectrometer to allow sampling of ions for subsequent spectroscopic analysis, and the sampling interface is An inlet for receiving a fixed amount of particles containing ions for the aforementioned spectroscopic analysis from an ion source, A skimmer positioned downstream of the inlet, having an opening through which particles from the inlet pass; An extraction lens positioned downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer, An adjustable voltage source that applies a bias voltage to the extraction lens to generate an electric field in at least the region between the extraction lens and the skimmer, The system includes a controller configured to control the adjustable voltage source to apply a bias voltage to the extraction lens (i.e., to control the bias voltage to the extraction lens) in order to control the reduced electric field in the region directly downstream of the skimmer.

[0074] The sampling interface is part of a mass spectrometer configured to allow sampling of ions from the generated plasma and to guide the sampled ions to a mass spectrometer for subsequent spectroscopic analysis and detection. The sampling interface can be considered a system for supplying a portion of the ions generated in the plasma of the mass spectrometer.

[0075] A sample may be introduced into a plasma (for example, a torch as described in other parts of this disclosure). A certain amount of particles are emitted from the plasma, and the certain amount of particles may include ionized and non-ionized particles. The certain amount of particles includes at least some of the ions of the sample ("sample ions") intended to be analyzed by spectroscopic analysis. Thus, the certain amount of particles may be received from an ion source confined in the plasma, and the extraction lens may be configured to extract ions from the plasma.

[0076] The sampling interface includes an inlet. The inlet typically includes an opening or orifice through which some particles from the plasma can pass. The inlet may also be a sampling cone (also known as a sampler). The inlet may allow only some of the particles from the plasma to pass through its opening toward the analyzer of the mass spectrometer. The analyzer may be any type suitable for spectroscopic analysis, for example, a quadrupole mass spectrometer.

[0077] The skimmer is a component of the sampling interface and has an opening through which particles (including sample ions) can pass, enabling the movement of the mass spectrometer to the analyzer. Typically, the skimmer is a conical component with a circular orifice (opening) at its apex. The skimmer narrows and collimates the particle beam by "skimming" or removing (preventing the passage of) the outer portion of the particle beam. The skimmer may also function as a partial barrier between regions with differential pressure, for example, as part of a differential pump transition from an atmospheric pressure region where plasma is generated to a low-pressure region of the mass spectrometer. The skimmer may be grounded, i.e., maintained at zero volts.

[0078] The direction of movement of the particles (i.e., the direction in which they pass through the inlet and the opening of the skimmer) is expressed as the component being located "downstream" or "upstream". Generally, the particles move through the inlet and then move downstream toward the mass spectrometer.

[0079] The extraction lens extracts charged particles (or ions) from the plasma and focuses these ions to form a narrow ion beam that travels toward the mass spectrometer. Efficient ion extraction by the extraction lens regulates the kinetic energy of the extracted ionized particles, thereby improving analytical sensitivity.

[0080] The adjustable voltage source is used to apply a voltage (or potential difference) to the extraction lens, generating an electric field between the extraction lens and the skimmer (the skimmer itself may be grounded). The magnitude of the voltage applied by the adjustable voltage source can be easily changed or adjusted by the user (e.g., via a controller).

[0081] The region immediately downstream of the skimmer is the region through which all particles that have passed through the skimmer opening pass. The region immediately downstream of the skimmer may be a chamber located between the skimmer and the extraction lens.

[0082] The controller may be an element (including an element implemented in a computer) used to send commands to the adjustable voltage source to adjust the voltage output from the voltage source. The controller may further receive commands from a user to make such adjustments. The controller may also receive measured values ​​from the system (e.g., values ​​measured by sensors in the system) and use such measured values ​​to make processing decisions. For example, the measured values ​​may be used in an algorithm predefined by the controller to determine the magnitude of the bias voltage applied to the extraction lens and to calculate the adjustments to be made to the magnitude of the voltage applied by the voltage source. The controller comprises a computer processor and computer-readable data storage, the processor executing a program or algorithm obtained from the data storage to operate or control other elements in the system.

[0083] The reduced field is a physical parameter with a defined meaning in the art. The reduced field T is defined as the ratio of the electric field E (here, in the region at least between the extraction lens and the skimmer) to the number density n (here, in the region immediately downstream of the skimmer). The number density can be considered to represent the number of neutral particles per unit volume (in other words, neutral particles in the background gas or collision gas). The ratio known as the reduced field has units in Townsend (Td) (e.g., https: / / en.wikipedia.org / wiki / Townsend_(unit) See (accessed June 15, 2023). This unit is 10 -21 Vm 2 This can sometimes be equivalent to the Townsend number, and this ratio is sometimes called the Townsend number. Therefore, JPEG2026521073000003.jpg9170

[0084] The reduced electric field T is related to the probability of collisions between ions and neutral particles in the relevant region (in this case, the region between the extraction lens and the skimmer).

[0085] In view of the above relationship, the reduced electric field (or Townsend number) T may be maintained at a constant value by increasing the electric field E in accordance with the increase in the number density n in the region directly downstream of the skimmer. The electric field E in the region directly downstream of the skimmer is directly related to the bias voltage applied to the extraction lens (in particular, E = V / d, where V is the difference between the skimmer bias and the voltage applied to the extraction lens, and d is the distance between the skimmer and the extraction lens). As described below, the number density n in the region directly downstream of the skimmer can be monitored by measuring system parameters such as pressure in that region. For example, by measuring the pressure P in this region according to the law of ideal gases (pV = nRT), the number density n with respect to volume V in the region between the skimmer and the extraction lens can be determined with approximate but accurate results. The temperature T in this region can be assumed to be constant, but it can also be measured by a sensor placed in the region between the skimmer and the extraction lens. It will be understood that R is the ideal gas constant. Therefore, the measurement result of the pressure P in the region between the skimmer and the extraction lens can be converted into the voltage to be applied to the extraction lens in order to maintain the reduced electric field (or Townsend number) T at a nearly constant value. Maintaining the reduced electric field at a nearly constant value allows for the consideration (or mitigation) of the degradation of the apparatus performance due to any (unavoidable) skimmer contamination that occurs during long experimental cycles.

[0086] The controller may be configured to determine the magnitude of the bias voltage applied to the extraction lens from the adjustable voltage source based on a measurement of a system parameter representing the number density in the region immediately downstream of the skimmer. This determination is made before controlling the magnitude of the bias voltage applied to the extraction lens by the adjustable voltage source. The determination may be based on a predefined relationship or algorithm, which may be stored in a memory device that can communicate with the controller and read from the memory device.

[0087] The system parameters may be measurable system characteristics such as pressure or temperature that represent the number density in the region immediately downstream of the skimmer. Measuring the system parameters provides numerical values ​​that can be used in further analysis in subsequent steps. Typically, the system parameters are measured by the sensors within the system and can return numerical values ​​(e.g., to a controller). In this disclosure, the system parameters represent the number density in the region immediately downstream of the skimmer and are therefore related to the reduced electric field (having a proportional or known relationship).

[0088] In one embodiment, the controller may be configured to receive a measured value of the system parameter representing the number density in the region immediately downstream of the skimmer. The controller may be configured to determine the magnitude of the bias voltage applied from the adjustable voltage source based on the measured value of the system parameter. Finally, the controller may be configured to control the adjustable voltage source to apply a bias voltage of a predetermined magnitude to the extraction lens, thereby controlling the reduced electric field in the region immediately downstream of the skimmer.

[0089] More specifically, the controller may be configured to determine, based on the measured value, the magnitude of the bias voltage applied to the extraction lens by the adjustable voltage source, and to maintain the reduced electric field at a substantially constant value. In other words, the magnitude of the bias voltage may be determined according to a predefined relationship between the measured values ​​of the system parameters and the applied bias voltage, and is used to maintain the reduced electric field (the ratio E / n above) at a substantially constant value. A substantially constant value means a value that is constant within a range of ±10%, or more preferably within a range of ±5%. A predetermined value of the reduced electric field T (also referred to as Townsend number) may be achieved using the predefined relationship between the measured values ​​of the system parameters and the applied bias voltage.

[0090] Typically, the predefined relationship between the measured value and the applied bias voltage for maintaining the reduced electric field constant is linear. The initial extracted electric field may be determined by an optimized setting of the extracted lens voltage to obtain the best sensitivity. The initial measured value of the system parameter (e.g., pressure) can be measured using a deposit-free, "clean" skimmer and calibration solution. The measured system parameter (e.g., pressure) can be measured a few minutes after the plasma generation state has been established to confirm that the temperature of the skimmer has stabilized. Thus, the reduced electric field (so-called Townsend number) is always the ratio of the initial extracted electric field strength to the initial measured value (e.g., pressure).

[0091] The system parameter may be the pressure in the region directly downstream of the skimmer. The measured values ​​of the system parameter may be obtained via a sensor located in the region directly downstream of the skimmer. For example, the sensor may be a sensor in a chamber located between the skimmer and the extraction lens.

[0092] In a specific embodiment, the sensor is a pressure sensor, and the system parameter is the pressure in the region immediately downstream of the skimmer. The pressure sensor may measure a numerical value of the pressure (e.g., instantaneous pressure) and return that value to another element (e.g., the controller). The change in pressure in the region immediately downstream of the skimmer may represent a change in the number density and may be mitigated by a change in the electric field in order to maintain a constant reduction electric field T (or Townsend number).

[0093] Further embodiments described are torches that generate inductively coupled plasma, wherein the torches are A torch tube comprising a support end and an open end, wherein a portion of the open end defines a cavity that at least partially confines the inductively coupled plasma, An injector tube having a bore, wherein the bore extends within the injector tube between an injector inlet end that receives the flow of sample and guides it into the bore and an injector outlet end that transports the flow of sample to the outside of the bore, and the injector tube is arranged to extend at least partially through the torch tube, A torch in which the diameter of the bore decreases between a first position and a second position, remains constant between the second position and a third position, or decreases further between the second position and a third position, and the first position is closer to the injector inlet end than the third position in the flow direction of the sample within the bore of the injector tube.

[0094] The torch is for generating plasma, more specifically, inductively coupled plasma. The torch allows for the introduction of gaseous samples, solution samples, dry aerosol samples, etc., into the plasma. The plasma generates gaseous and ionized particles of the sample, which are then transported from the plasma to the mass spectrometer.

[0095] The support end of the torch tube may be connected to or held by a housing, support structure, or support device, and the open end is provided with an opening for the torch tube to the bore. Since the diameter of the torch tube is larger than that of the injector tube, the injector tube is positioned to extend over at least a portion of the length of the cavity or bore extending within the torch tube, thereby positioning the injector tube coaxially with the torch tube for at least a portion of its length. The injector tube is positioned to pass at least partially through the torch tube such that the injector inlet end is closer to the support end of the torch tube than the injector outlet end is closer to the support end of the torch tube. The injector tube may extend over the entire length of the torch tube, but it is more preferable that it extends over only a portion of the length of the torch tube. Specifically, the end of the torch tube may extend outward beyond the end of the injector tube through which it passes. The sample may flow out of the bore of the injector tube and be delivered to the plasma generated in the cavity at the open end of the torch tube. The open end of the torch tube defines the cavity (or cavity, or void), and the opening of the open end is an opening to the partially open cavity. When in use, the cavity may contain the generated plasma entirely or partially. The size of the cavity at the open end may be defined by how far the injector tube extends within the torch tube.

[0096] The injector tube is provided with a through bore or hole. When the torch is used, the sample may be delivered through the bore of the injector tube to the plasma generated in the cavity of the torch tube. The injector tube is positioned so that the sample enters the bore of the injector tube at the injector inlet end and exits the bore of the injector tube at the injector outlet end.

[0097] The diameter of the bore of the injector tube is the size of the hole penetrating the injector tube in a direction perpendicular to the extending direction of the hole penetrating the injector tube. The extending direction can be considered as the axial direction, and the perpendicular direction can be considered as the radial direction. The first position, the second position, and the third position are different positions along the extending direction of the hole penetrating the injector tube.

[0098] Advantageously, the bore diameter within the injector tube is reduced in the flow direction (this reduction may be realized as a tapered or conical portion of the bore), which accelerates the flow of the sample through the injector tube. As a result, the sample enters a hotter plasma in the cavity of the torch tube (where ions from the plasma have higher energy and move at higher speeds), and the plasma may be more focused (may have a smaller diameter). Consequently, contamination and deposition observed in the downstream components of the torch are reduced.

[0099] When the described torch is combined with the described sampling interface, a more focused flow of charged particles is provided, allowing the charged particles to pass through the inlet opening and the skimmer orifice without obstruction. For example, since the bore diameter of the injector tube at the injector outlet end is 1.0 mm and the diameter of the inlet opening is 1.1 mm, the diameter of the charged particle beam is such that it can pass through the inlet opening without obstruction. This helps maintain a constant pressure between the inlet of the sampling interface and the skimmer, and as a result, according to this disclosure, the reduced electric field in the region immediately downstream of the skimmer can be better controlled. Therefore, the combination of the described torch and the sampling interface of this disclosure may yield certain advantages.

[0100] The bore diameter at the second position may be 110% or less of the bore diameter at the third position, and more preferably 105% or less of the bore diameter at the third position. In some embodiments, the bore diameter at the second position is equal to the bore diameter at the third position. In particular, between the second and third positions, the bore diameter is hardly or not reduced at all, and the bore diameter in this portion is substantially constant (cylindrical). This portion is closer to the injector outlet end than the enlarged portion of the bore. The extension of a portion of the injector tube over a finite length and having a substantially constant diameter forms a more collimated beam of particles generated from the plasma, reducing plasma instability and separation compared to a torch where the injector tube narrows only at the tip of the bore.

[0101] The bore diameter at the first position may exceed 200% of the bore diameter at the second position, exceed 300% of the bore diameter at the second position, or exceed 400% of the bore diameter at the second position. In other words, the bore diameter of the injector tube at the first position may exceed 2, 3, or 4 times the bore diameter of the injector tube at the second position. The degree of reduction in diameter between the first and second positions can be selected to obtain the required amount of acceleration of the sample flow through the bore of the injector tube when the torch is used.

[0102] The third position may be the injector outlet end of the injector tube. In other words, the portion of the tube between the second position and the third position may extend from the second position to the injector outlet end.

[0103] The bore diameter may include a conical section (or tapered section) extending between the first and second positions. To maintain a more layered and less turbulent flow of the sample through the bore, it is preferable that the bore diameter tapers smoothly compared to a stepped reduction in diameter.

[0104] The diameter of the bore at the first position may be equal to the diameter of the bore at the injector inlet end. In other words, the bore extending from the injector inlet end to the first position may have a substantially constant diameter.

[0105] The injector tube is positioned to pass at least partially through the torch tube, defining a channel between the outer surface of the injector tube and the inner wall of the torch tube for the flow of confinement gas. In at least a specific region along the length of the torch tube, the channel is an annular channel surrounding the injector tube. The confinement gas may be used to radially confine the plasma generated at the open end (and / or near the open end) of the torch tube when the torch is in use. The confinement gas may also serve to cool the wall of the torch tube closest to the generated plasma when the torch is in use.

[0106] The outer diameter of the injector tube may be larger at the injector outlet end than at the injector inlet end. In other words, the outer diameter of the injector tube may increase as it approaches the open end of the torch tube. In a specific embodiment, the outer diameter of the injector tube may be conical or tapered outward in the portion closest to the injector outlet end, increasing from a narrowed diameter portion to a widened diameter portion, with the maximum outer diameter located at the injector outlet end. This can be useful for controlling the shape or flow direction of the confined gas passing through the channel between the outer diameter of the injector tube and the inner surface of the torch tube.

[0107] The outer diameter of the injector tube may have a tapered portion terminating at the injector outlet end, and the outer diameter of the injector tube may decrease in the direction extending from the injector outlet end toward the injector inlet end. The tapered portion may extend only to a portion of the longitudinal length between the injector outlet end and the injector inlet end. Specifically, the tapered portion may be an enlarged cone (or frustocone) region on the outer surface of the injector tube, located at the end of the injector tube closest to the injector outlet end (and thus having the widest diameter at the injector outlet end). The tapered portion maintains a high flow velocity of the already accelerated gas passing through the channel defined between the outer surface of the injector tube and the inner surface of the torch tube, and guides the flow of the confined gas through the containment section at the open end of the torch tube.

[0108] The radial distance between the outer surface of the injector tube and the inner wall of the torch tube may be substantially constant in the region aligned with the tapered portion of the outer surface of the injector tube. In other words, the annular channel defined between the outer surface of the injector tube and the inner wall of the torch tube may have a substantially constant radial width in the region aligned with the tapered portion of the outer surface of the injector tube and extending axially. The distance between the enlarged conical portion (i.e., the tapered portion) of the outer surface of the injector tube and the inner surface of the torch tube can be selected so as to sufficiently accelerate the axial velocity of the gas flowing from the support end of the torch tube toward the open end of the torch tube, thereby providing good containment of the generated inductively coupled plasma.

[0109] The bore extending between the support end and the open end of the torch tube, through which the injector tube extends, may include a tapered section, the diameter of the bore extending to the torch tube increasing between the inlet to the tapered section and the outlet from the tapered section, the inlet to the tapered section being closer to the support end than the outlet from the tapered section. The diameter of the bore extending to the torch tube is the diameter or spacing between the inner walls of the holes or cavities penetrating the torch tube. In other words, the bore of the torch tube expands in diameter over a portion of its length compared to the preceding portion. This expanded or tapered portion of the bore of the torch tube may be aligned with a conical or tapered portion of the outer surface of the injector tube, as described above. This further facilitates the acceleration and control of the flow direction of the confined gas passing through the channel between the outer surface of the injector tube and the inner surface of the torch tube.

[0110] The entire tapered portion of the outer surface of the injector tube may be aligned, at least in part, with the tapered section of the bore that penetrates the torch tube. In other words, along the axial direction, the tapered portion of the outer surface of the injector tube expands in diameter as it approaches the injector outlet end, and the bore extending into the torch tube also expands in diameter, at least in the same axial portion. This allows the channel (the annular channel defined between the outer surface of the injector tube and the inner wall of the torch tube, through which the confinement gas flow passes) to maintain a constant (or nearly constant) radial width. The radial width can be selected so that the axial velocity of the gas flowing from the support end of the torch tube toward the open end of the torch tube is sufficiently accelerated, and the plasma is well confined. The tapered portion of the outer surface of the injector tube may extend along the same axial length as the tapered section of the bore extending through the torch tube, or the tapered portion of the outer surface of the injector tube may extend along a shorter axial length than the tapered section of the bore extending through the torch tube, provided that a portion of the tapered section of the bore extending through the torch tube is coaxial with the entire tapered portion of the outer surface of the injector tube.

[0111] The injector tube may be positioned to at least partially penetrate the torch tube such that the housing section at the open end of the torch tube extends beyond the injector outlet end of the injector tube. In the housing section, the portion of the torch tube that extends beyond the injector outlet end of the injector tube from the open end may exceed five times the diameter of the injector bore at the injector outlet end, exceed seven times, or exceed ten times the diameter of the injector bore at the injector outlet end.

[0112] The walls of the bore, which extend within the torch tube and form the inner wall of the torch tube, may define a cylinder or a partial cone within the housing section.

[0113] The torch may further include a load coil positioned around at least a portion of the outer surface of the torch tube within the housing section. The load coil may be wound over a portion of the radial length of the housing section. The load coil serves to conduct a high-power, high-frequency current and, together with other components of the torch, generates a strong magnetic field for producing a more stable, high-temperature plasma. The axial distance between the injector outlet end of the injector tube and the nearest surface of the load coil in the axial direction (in other words, the axial distance between the torch tube and the injector tube) may be greater than 0 and less than the diameter of the injector bore at the injector outlet end, more specifically less than 2 mm. The axial distance between the open end of the torch tube and the nearest surface of the load coil in the axial direction may be 3 mm or more, and / or more than twice or more than three times the diameter of the injector bore at the injector outlet end. The specified distance between the injector outlet end and the load coil reduces loss due to high plasma temperature and also reduces damage to the torch. Furthermore, the distance between the load coil and the open end of the torch tube can further increase the plasma temperature and allow for better collimation of the particle flow from the plasma. Therefore, the load coil arrangement can be applied to the torch without the various other novel configurations specified above (e.g., an injector tube with a reduced bore), and still provides technical advantages.

[0114] Another embodiment is a torch positioned near the inlet of a sampling interface used in a mass spectrometer, wherein the torch is positioned so that a certain amount of particles from the inductively coupled plasma generated by the torch during use pass through the inlet of the sampling interface. The sampling interface may be as described above, or it may be another sampling interface having an inlet. Here, the bore diameter of the injector tube at the injector outlet end of the torch may be smaller than the diameter of the opening at the inlet of the sampling interface, and the certain amount of particles received from the torch at the inlet may pass through the opening.

[0115] Another embodiment is the sampling interface described above used in a mass spectrometer, wherein a fixed amount of particles from an ion source is received at the inlet from a torch that generates inductively coupled plasma, the torch may be the inductively coupled plasma generating torch described above, or a torch of another configuration that generates inductively coupled plasma. The bore diameter of the injector tube at the injector outlet end of the torch may be smaller than the diameter of the opening at the inlet of the sampling interface, and the fixed amount of particles received from the torch at the inlet may pass through the opening.

[0116] By using the described sampling interface in combination with the described torch, the advantages of each configuration are combined to further reduce the degradation of the instrument's performance during long-duration spectroscopic analysis.

[0117] During use, the inductively coupled plasma generated by the torch may generate a certain amount of ionized particles to be received at the inlet. During use, the inductively coupled plasma may be generated within the containment section of the torch tube, or partially within the containment section. The plasma may be generated within the containment section, but may also extend beyond the open end of the torch tube.

[0118] The inlet of the sampling interface may include a sampling cone. The sampling cone, together with the skimmer, can contribute to providing a differential aperture that separates the plasma generated in the atmosphere from the downstream mass spectrometer and the detector located in a high vacuum (i.e., low pressure). Typically, the sampling cone is larger than the skimmer, has a less pointed tip, and usually has a larger diameter for the through-orifice or opening. While the central cone of the skimmer is more acute, the sampling cone generally has a central cone with a shallower central angle.

[0119] As described above, the bore diameter of the injector tube at the injector outlet end of the torch may be smaller than the diameter of the opening at the inlet of the sampling interface, and the constant amount of particles received from the torch at the inlet may pass through the opening (preferably substantially unobstructed). Advantageously, this allows particles trapped in the central plasma channel of the plasma generated by the torch to pass through the inlet unobstructed, contributing to avoiding deposition at the opening. In one embodiment, the bore diameter of the injector tube at the injector outlet end is 1.0 mm, and the diameter of the opening at the inlet to the sampling interface is 1.1 mm. Unobstructed passage of charged particle flow contributes to maintaining a constant pressure in the interface region between the inlet of the sampling interface and the skimmer. This allows for better control of the reduced electric field in the region immediately downstream of the skimmer, and thus improves the performance of the disclosed sampling interface.

[0120] Further described embodiments relate to methods for sampling ions within a mass spectrometer for use in subsequent spectroscopic analysis. Where the method refers to features common to the sampling interface and torch described above, the same descriptions or characteristics relating to these common features also apply to the method. The method described above is: A sampling interface, An inlet for receiving a fixed amount of particles containing ions for the aforementioned spectroscopic analysis from an ion source, A skimmer positioned downstream of the inlet, having an opening through which particles from the inlet pass; An extraction lens positioned downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer, The sampling interface is provided, comprising: an adjustable voltage source that applies a bias voltage to the extraction lens to generate an electric field in at least the region between the extraction lens and the skimmer; A method comprising applying a bias voltage to the extraction lens to control the reduced electric field in the region immediately downstream of the skimmer using the adjustable voltage source.

[0121] The reduced electric field may be defined as the ratio of the electric field in the region between the extraction lens and the skimmer to the number density in the region immediately downstream of the skimmer.

[0122] The method may further include, before the application, measuring a system parameter representing the number density in the region immediately downstream of the skimmer and obtaining a measurement of the system parameter, and determining the magnitude of the bias voltage to be applied from the adjustable voltage source based on the measurement.

[0123] The magnitude of the bias voltage applied to the extraction lens may be determined based on a predefined relationship between the bias voltage and the system parameters. The magnitude of the bias voltage may be determined to maintain the reduced electric field at a substantially constant value. A substantially constant value may be a value that is constant within a range of ±10%, or more preferably within a range of ±5%.

[0124] The system parameter may be the pressure in the region directly downstream of the skimmer. The value of the system parameter may be measured via a sensor (such as a pressure sensor) located in the region directly downstream of the skimmer.

[0125] The method may also include providing a torch for generating inductively coupled plasma, wherein the inlet is positioned such that a certain amount of particles from an ion source are received at the inlet from the torch for generating the inductively coupled plasma. The torch may be the inductively coupled plasma generating torch described above, or it may be a torch with another configuration for generating inductively coupled plasma.

[0126] Following the provision described above, the method may further include generating a certain amount of particles containing ions for spectroscopic analysis by generating an inductively coupled plasma with the torch.

[0127] The method may further include maintaining the pressure in the region between the inlet and the skimmer at approximately a constant magnitude. The region between the inlet and the skimmer may also be considered the interface region, and the pressure in the region (also referred to as the interface pressure) is preferably maintained at approximately a constant magnitude (within ±10% of a predefined value). The constant pressure is maintained by configuring the components of the sampling interface and the torch so that the charged particle flow from the plasma passes through the torch and the sampling interface with virtually no obstruction (this also reduces deposition or clogging at each opening in the components of the sampling interface). There are two important factors that contribute to achieving unobstructed flow, both provided by the torch described above. These factors are that (a) the plasma becomes more focused as a result of the diameter of the injector tube of the torch decreasing toward the injector outlet end, and (b) the charged particle flow emitted from the plasma generated by the torch is smaller than the diameter of the opening of the inlet. Therefore, performance is particularly improved by using the disclosed sampling interface in combination with the disclosed torch.

[0128] As described above, the sampling interface may be configured in association with at least one of the following mass spectrometers: atmospheric pressure plasma ion source mass spectrometry (which may use low-pressure or high-pressure plasma ion sources), e.g., ICP-MS, microwave plasma mass spectrometry (MP-MS) or glow discharge mass spectrometry (GD-MS) or optical plasma mass spectrometry (e.g., laser-induced plasma), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and ion chromatography-mass spectrometry (IC-MS). Furthermore, other ion sources may include electron ionization (EI), real-time direct analysis (DART), desorption electrospray ionization (DESI), atmospheric pressure afterglow (FAPA), low-temperature plasma (LTP), dielectric barrier discharge (DBD), helium plasma ionization source (HPIS), dopant-assisted atmospheric pressure photoionization (DAPPI), and atmospheric pressure desorption ionization (ADI). Those skilled in the art will understand that this list is not intended to be exhaustive.

[0129] In another embodiment, there is a mass spectrometer equipped with the sampling interface and / or torch described above. The mass spectrometer may be suitable for inductively coupled plasma mass spectrometry.

Claims

1. A sampling interface for use in a mass spectrometer, wherein the sampling interface is configured to allow sampling of ions for subsequent spectroscopic analysis in the mass spectrometer, and the sampling interface is An inlet that receives a fixed amount of particles containing ions for spectroscopic analysis from an ion source, A skimmer positioned downstream of the inlet, having an opening through which particles from the inlet pass; An extraction lens positioned downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer, An adjustable voltage source that applies a bias voltage to the extraction lens to generate an electric field in at least the region between the extraction lens and the skimmer, A sampling interface comprising: a controller configured to control the adjustable voltage source to apply a bias voltage to the extraction lens in order to control the reduced electric field in the region immediately downstream of the skimmer.

2. The sampling interface according to claim 1, wherein the reduced electric field is defined as the ratio of the electric field in the region between the extraction lens and the skimmer to the number density in the region immediately downstream of the skimmer.

3. The sampling interface according to claim 1 or 2, wherein the controller is configured to receive a measured value of a system parameter representing the number density in the region immediately downstream of the skimmer, and to determine the magnitude of the bias voltage applied by the adjustable voltage source based on the measured value of the system parameter.

4. The sampling interface according to claim 3, wherein the controller is configured to determine the magnitude of the bias voltage applied by the adjustable voltage source based on the measured value, so as to maintain the reduced electric field at a substantially constant value.

5. The sampling interface according to claim 4, wherein a nearly constant value is a constant value within a range of ±10%, or more preferably a constant value within a range of ±5%.

6. The sampling interface according to any one of claims 1 to 5, wherein the system parameter is the pressure in the region directly downstream of the skimmer.

7. The sampling interface according to any one of claims 1 to 6, wherein the measured values ​​of the system parameters are measured by a sensor located in the region directly downstream of the skimmer.

8. The sampling interface according to claim 7, as dependent on claim 6, wherein the sensor is a pressure sensor.

9. The sampling interface according to any one of claims 1 to 8, wherein the inlet is configured to receive a fixed amount of particles from an inductively coupled plasma ion source.

10. A torch for generating inductively coupled plasma, A torch tube comprising a support end and an open end, wherein a portion of the open end defines a cavity that at least partially confines the inductively coupled plasma, An injector tube having a bore, wherein the bore extends through the injector tube between an injector inlet end that receives a flow of sample and guides it into the bore and an injector outlet end that transports the flow of sample to the outside of the bore, and the injector tube is arranged to extend at least partially through the torch tube, A torch in which the diameter of the bore decreases between a first position and a second position, and is constant or decreases between the second position and a third position, wherein the first position is closer to the injector inlet end than the third position in the flow direction of the sample within the bore of the injector tube.

11. The torch according to claim 10, wherein the diameter of the bore at the second position is 110% or less of the diameter of the bore at the third position.

12. The torch according to claim 10 or 11, wherein the diameter of the bore at the second position is equal to the diameter of the bore at the third position.

13. The torch according to any one of claims 10 to 12, wherein the diameter of the bore at the first position is more than twice the diameter of the bore at the second position, preferably more than three times the diameter of the bore at the second position.

14. The torch according to any one of claims 10 to 13, wherein the third position is the injector outlet end of the injector tube.

15. The torch according to any one of claims 10 to 14, wherein the diameter of the bore includes a conical section extending between the first position and the second position.

16. The torch according to any one of claims 10 to 15, wherein the injector tube is arranged to extend at least partially through the torch tube, and a channel for the passage of a confined gas flow is defined between the outer surface of the injector tube and the inner wall of the torch tube.

17. The torch according to claim 16, wherein the outer diameter of the injector tube is larger at the injector outlet end than at the injector inlet end.

18. The torch according to claim 16 or 17, wherein the diameter of the outer surface of the injector tube has a tapered portion terminating at the injector outlet end, and the diameter of the outer surface of the injector tube decreases in the direction extending from the injector outlet end toward the injector inlet end.

19. The torch according to claim 18, wherein the radial distance between the outer surface of the injector tube and the inner wall of the torch tube is substantially constant in the region aligned with the tapered portion of the outer surface of the injector tube.

20. A torch according to any one of claims 10 to 19, wherein a bore extending through the torch tube between the support end and the open end and through which the injector tube extends includes a tapered section, the diameter of the bore extending through the torch tube increases between the inlet to the tapered section and the outlet from the tapered section, and the inlet to the tapered section is closer to the support end than the outlet from the tapered section.

21. The torch according to claim 20, as dependent on claim 18 or 19, wherein the entire tapered portion of the outer surface of the injector tube is aligned with the tapered section of the bore that penetrates the torch tube, at least in part.

22. The torch according to any one of claims 10 to 21, wherein the injector tube is arranged to extend at least partially through the torch tube such that the housing section of the torch tube extends beyond the injector outlet end of the injector tube at the open end.

23. The torch according to claim 22, wherein the wall of the bore extending through the torch tube defines a cylinder or a partial cone in the housing section.

24. The torch according to claim 22 or 23, further comprising a load coil disposed around at least a portion of the outer surface of the torch tube in the housing section.

25. The torch according to claim 24, wherein the axial distance between the injector outlet end of the injector tube and the load coil is greater than 0, preferably less than 2 mm.

26. The torch according to claim 24 or 25, wherein the axial distance between the open end of the torch tube and the load coil is 3 mm or more.

27. A torch according to any one of claims 10 to 26, positioned near the inlet of a sampling interface used in a mass spectrometer, wherein a certain amount of particles from the inductively coupled plasma generated by the torch during use pass through the inlet of the sampling interface.

28. The torch according to claim 27, wherein the diameter of the bore of the injector tube of the torch at the injector outlet end is smaller than the diameter of the opening at the inlet of the sampling interface, and a certain amount of particles received from the torch at the inlet pass through the opening.

29. The torch according to claim 27 or 28, wherein the sampling interface is the sampling interface described in any one of claims 1 to 9.

30. A sampling interface for use in a mass spectrometer, according to any one of claims 1 to 9, A sampling interface according to any one of claims 10 to 26, wherein the inlet is configured to receive a fixed amount of particles from an ion source from a plasma generated by a torch for generating an inductively coupled plasma.

31. The sampling interface according to claim 30, wherein the diameter of the bore of the injector tube of the torch at the injector outlet end is smaller than the diameter of the opening at the inlet of the sampling interface, and a certain amount of particles received from the torch at the inlet pass through the opening.

32. A method for sampling ions with a mass spectrometer for subsequent spectroscopic analysis, To provide a sampling interface, wherein the sampling interface is An inlet that receives a fixed amount of particles containing ions for spectroscopic analysis from an ion source, A skimmer positioned downstream of the inlet, having an opening through which particles from the inlet pass; An extraction lens positioned downstream of the skimmer, configured to extract ions from particles that have passed through the opening of the skimmer, The sampling interface is provided, comprising: an adjustable voltage source that applies a bias voltage to the extraction lens to generate an electric field in at least the region between the extraction lens and the skimmer; A method comprising applying a bias voltage to the extraction lens using the adjustable voltage source in order to control the reduced electric field in the region immediately downstream of the skimmer.

33. The method according to claim 32, wherein the reduced electric field is defined as the ratio of the electric field in the region between the extraction lens and the skimmer to the number density in the region immediately downstream of the skimmer.

34. The method according to claim 32 or 33, further comprising: measuring a system parameter representing the number density in the region immediately downstream of the skimmer and obtaining a measurement of the system parameter before applying the said voltage; and determining the magnitude of the bias voltage applied by the adjustable voltage source based on the measurement.

35. The method according to claim 34, wherein the magnitude of the bias voltage is determined based on the measured value to maintain the reduced electric field at a substantially constant value.

36. The method according to claim 35, wherein a nearly constant value is a constant value within a range of ±10%, or more preferably a constant value within a range of ±5%.

37. The method according to any one of claims 32 to 36, wherein the system parameter is the pressure in the region directly downstream of the skimmer.

38. The method according to any one of claims 32 to 37, comprising providing a torch for generating inductively coupled plasma, wherein the torch is arranged such that a certain amount of particles from an ion source are received at the inlet from the inductively coupled plasma generated by the torch.

39. The method according to claim 38, further comprising generating a certain amount of particles containing ions for spectroscopic analysis by generating an inductively coupled plasma with the torch before applying the aforementioned coating.

40. The method according to claim 39, further comprising maintaining the pressure in the region between the inlet and the skimmer at a substantially constant level.

41. The method according to any one of claims 38 to 40, wherein the torch is a torch for generating an inductively coupled plasma according to any one of claims 10 to 26.

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