TEMPERATURE CONTROL PLASMA SOURCE ANALYZER ARRANGEMENT AND TEMPERATURE-CONTROLLED GAS FLOW-PLASMA SOURCE ANALYSIS METHOD

Abstract

The invention relates to a temperature control plasma source analyzer arrangement (1) comprising a plasma source (3), at least one preheating device (2), preferably comprising a temperature control means (21) for heating and/or cooling at least one gas flow of the plasma source (3) relative to room temperature, of, and an analyzer (4); wherein the at least one gas flow comprises a sample gas flow (5) with a sample aerosol (15), the plasma source (3) is configured to ionize the sample aerosol (15) of the sample gas flow (5), and the analyzer (4) is configured to analyze the ionized sample aerosol (15); wherein the preheating device (2) is configured to increase temperature of the at least one gas flow; the preheating device (2) is located in front of the plasma source (3) so that the at least one gas flow reaches the plasma source (3) only after leaving the preheating device (2); the preheating device (2) is configured to controllably increase the temperature of the at least one gas flow; and the arrangement (1) is designed as a modular system, wherein the preheating device (2) is constructed as a separate module

Claims

1. A temperature control plasma source analyzer arrangement comprising a plasma source; at least one preheating device, preferably comprising a temperature control means for heating, in particular preheating, and/or cooling at least one gas flow of the plasma source relative to room temperature; and an analyzer; wherein the at least one gas flow comprises a sample gas flow with a sample aerosol; the plasma source is configured to ionize the sample aerosol of the sample gas flow; and the analyzer is configured to analyze the ionized sample aerosol; wherein the preheating device is configured to increase the temperature of the at least one gas flow; the preheating device is located in front of the plasma source so that the at least one gas flow reaches the plasma source only after leaving the preheating device; the preheating device is configured to controllably increase the temperature of the at least one gas flow; and the arrangement is designed as a modular system, wherein the preheating device is constructed as a separate module.

2. The temperature control plasma source analyzer arrangement according to claim 1, wherein the preheating device is configured to preheat the sample gas flow of the plasma source such that the sample gas flow has, throughout an entire period of time between a start of an operation of the analyzer and a stop of the operation of the analyzer, a constant injection temperature T.sub.IN at an injection site where the sample gas flow is introduced in the plasma source; or wherein the preheating device is configured to preheat the sample gas flow of the plasma source such that the sample gas flow has, preferably throughout the entire period between the start of the operation of the analyzer and the stop of operation of the analyzer, a variable injection temperature at the injection site where the sample gas flow is introduced into the plasma source, wherein the variable injection temperature varies, in particular oscillates, more particular oscillates sinusoidally, around and/or about a predetermined constant temperature value, preferably with a deflection whose value is less than 5%, in particular less than 2.5%, and more preferably less than 1.25% of the predetermined constant temperature value.

3. The temperature control plasma source analyzer arrangement according to claim 2, wherein the preheating device is configured to preheat the sample gas flow of the plasma source such that the sample gas flow has a constant injection temperature T.sub.IN at the injection site which is higher than 200 C., in particular higher than 400 C., or wherein the preheating device is configured to preheat the sample gas flow of the plasma source such that the sample gas flow has a variable injection temperature with a predetermined constant temperature value which is higher than 200 C., in particular higher than 400 C.

4. The temperature control plasma source analyzer arrangement according t claim 1, wherein the preheating device is designed as externally heated metal capillaries or metal tubes and/or internal heating elements and/or heating coils and/or heating filaments and/or heating grids or heating braids and/or external heating elements and/or heating lines and/or laser heating and/or a pre-plasma and/or electromagnetic radiation sources.

5. The temperature control plasma source analyzer arrangement according to claim 1, wherein the preheating device comprises at least one control unit, at least one gas transfer line and at least one temperature control unit.

6. The temperature control plasma source analyzer arrangement according to claim 1, wherein the preheating device is designed to controllably increase the temperature on the basis of adjustable fixed control parameters and/or adjustable control parameters with a temperature measuring element in a control loop.

7. The temperature control plasma source analyzer arrangement according to claim 1, wherein the preheating device is designed to control a temperature in a cooling gas flow and/or an auxiliary gas flow on the basis of adjustable fixed control parameters and/or adjustable control parameters with a temperature measuring element in a control loop.

8. The temperature control plasma source analyzer arrangement according to claim 1, wherein preheating the at least one gas flow reduces or allows for reducing a residence time of the sample gas flow with the sample aerosol in the plasma source, preferably wherein a shortened residence time effects or allows for a reduction of diffuse losses of extractable ions and element fractionation.

9. A temperature-controlled gas flow-plasma source analysis method using a temperature control plasma source analyzer arrangement according to claim 1 comprising the following steps: setting control parameters in the preheating device; feeding at least one gas flow into the preheating at a start temperature T.sub.S, wherein the at least one gas flow comprises a sample gas flow with a sample aerosol; heating the at least one gas flow in the preheating device to an injection temperature T.sub.IN, wherein T.sub.S<T.sub.IN; feeding the sample gas flow into the plasma source at injection temperature T.sub.IN; heating the sample gas flow in the plasma source to extraction temperature T.sub.EX with ionization of the sample aerosol of the sample gas flow, wherein T.sub.S<T.sub.IN<T.sub.EX; extracting ionized sample aerosol at extraction temperature T.sub.EX and feeding to the analyzer; performing the analysis of the ionized sample gas flow in the analyzer.

10. The temperature-controlled gas flow-plasma source analysis method according to claim 1, wherein heating the at least one gas flow in the preheating device to the injection temperature T.sub.IN comprises heating the sample gas flow in the preheating device to an injection temperature T.sub.IN which is constant throughout an entire period of time between a start of an operation of the analyzer and a stop of the operation of the analyzer; or wherein heating the at least one gas flow in the preheating device to the injection temperature T.sub.IN comprises heating the sample gas flow in the preheating device to a variable injection temperature, wherein the variable injection temperature varies, in particular oscillates, more particular oscillates sinusoidally, around and/or about a predetermined constant temperature value, preferably with a deflection whose value is less than 5%, in particular less than 2.5%, and more preferably less than 1.25% of the predetermined constant temperature value.

11. The temperature-controlled gas flow-plasma source analysis method according to claim 10, wherein the sample gas flow is heated in the preheating device to an injection temperature T.sub.IN which is higher than 200 C., in particular higher than 400 C.; or wherein the sample gas flow is heated in the preheating device to a variable injection temperature with a predetermined constant temperature value which is higher than 200 C., in particular higher than 400 C.

12. The temperature-controlled gas flow-plasma source analysis method according to claim 9, wherein the start temperature T.sub.S is room temperature.

13. The temperature-controlled gas flow-plasma source analysis method according to claim 9, wherein the at least one gas flow with its temperature increased in the preheating device is formed from the sample gas flow or the sample gas flow and the auxiliary gas flow or the sample gas flow and the cooling gas flow or the sample gas flow and the auxiliary gas flow and the cooling gas flow.

14. The temperature-controlled gas flow-plasma source analysis method according to claim 9, wherein the sample aerosol in the sample gas flow is partially pre-evaporated in the preheating device.

15. The temperature-controlled gas flow-plasma source analysis method to claim 9, wherein the setting of control parameters in the preheating device is realized via fixed control parameters and/or control parameters with a temperature measuring element in a control loop.

16. The temperature-controlled gas flow-plasma source analysis method to claim 9, wherein heating the at least one gas flow in the preheating device to the injection temperature T.sub.IN is carried out such that a share of energy to be applied in the plasma source for the evaporation and ionization of the sample aerosol in the sample gas flow is reduced.

17. Use of the temperature control plasma source analyzer arrangement according to claim 1 utilizing the temperature-controlled gas flow-plasma source analysis method for controlling the temperature of at least one gas flow of a plasma source.

Description

[0108] In describing the invention, reference will be made to the accompanying figures in the following description of the figures, wherein this serves in illustrating the invention and is not to be considered as limiting. Shown are:

[0109] FIG. 1 an exemplary embodiment of a plasma source designed as an ICP plasma source according to the prior art;

[0110] FIG. 2 an exemplary schematic depiction of the processes in the plasma of a plasma source according to FIG. 1;

[0111] FIG. 3 an exemplary embodiment of the basic structure of a preheating device of a temperature control plasma source analyzer arrangement according to the invention;

[0112] FIG. 4 an exemplary first embodiment of a temperature control plasma source analyzer arrangement according to the invention;

[0113] FIG. 5 an exemplary second embodiment of a temperature control plasma source analyzer arrangement according to the invention;

[0114] FIG. 6 an exemplary depiction of various states in the process flow of a prior art ICP-MS comprising a) temperature profile, b) sample aerosol evaporation, c) total ionization and d) diffusion loss;

[0115] FIG. 7 an exemplary depiction of various parameters in the process flow of the temperature-controlled gas flow-plasma source analysis method according to the invention comprising [0116] a) temperature profile, b) sample aerosol evaporation, c) total ionization and d) diffusion loss and

[0117] FIG. 8 an exemplary selection of design variants of the temperature control unit 21 of the preheating device 2 (FIG. 8a) to g)).

[0118] FIG. 1 shows the structure of a plasma source 3 designed as an ICP plasma source according to the prior art. A plasma 14 is inductively excited with radio waves inside a plasma torch 8 via an RF coil 9. The operationally required gases are supplied to the plasma torch 8 via the inlets for the sample gas feed 51, auxiliary gas feed 61 and cooling gas feed 71. The sample aerosol 15 is fed into the plasma 14 with the sample gas flow 5 at the injection site of the sample gas flow 12. After evaporation of the sample aerosol 15 and ionization, the ions are extracted from the plasma at the site of ion extraction 13. This is done via the sampler cone 10 and the skimmer cone 11.

[0119] FIG. 2 schematically depicts an example of the processes in the plasma 14 of a plasma source according to FIG. 1. The arrangement of the gas feeds 51, 61, 71 within the plasma torch 8 corresponds to FIG. 1. The sample aerosol 15 is introduced into the plasma 14 at the injection site of the sample gas flow 12. The sample aerosol 15 is progressively evaporated as it passes through the plasma 14 from the injection site 12 to the extraction site 13 (represented in the depiction by the decreasing size of the black circles representing the sample aerosol 15). Furthermore, the released atoms of the sample are gradually ionized by the energy of the surrounding plasma 14. Released atoms/ions are subject to diffusion and are lost from the central trajectory to outer regions of the plasma 14 (diffusion loss). Only the portion of ions that can be captured by the sampler cone 10 at the extraction site 13 is usable and is conveyed to the interface of the analyzer 4 preferentially designed as a mass spectrometer.

[0120] FIG. 3 shows an exemplary embodiment of the basic structure of a preheating device 2 of a temperature control plasma source analyzer arrangement 1 according to the invention. Same comprises a temperature control unit 21, a gas transfer line 22, a housing insulation 23 and a control unit 24. The sample gas flow 5 with the sample aerosol 15 is directed through the preheating device 2 for the purpose of temperature control. The temperature control unit 21 is in contact with the gas transfer line 22 for the purpose of temperature control of the sample aerosol 15. The temperature control unit 21 is connected to the control unit 24 via a connecting cable 26. The control unit 24 regulates the temperature controlling operation of the temperature control unit 21 for the purpose of controlling the temperature of the sample aerosol 15. In this context, temperature control means the regulated temperature change of the sample aerosol 15 in the sample gas flow 5 from the start temperature T.sub.S to the injection temperature T.sub.IN, wherein T.sub.S<T.sub.IN, so that the share of energy to be applied in the plasma source 3 for the evaporation and ionization of the sample aerosol 15 in the sample gas flow 1 is reduced.

[0121] To shield against the environment (thermal, electrical, etc.) as well as to protect the user and the existing measuring equipment, the cited components are typically located in an insulating housing 23. In order to easily integrate the preheating device 2 into existing measuring apparatus as a module, it is typically equipped with two adapters 25, 31 which enable connection to both the existing primary sample apparatus 16 as well as to the plasma source 3.

[0122] FIG. 4 shows an exemplary first embodiment of a temperature control plasma source analyzer arrangement 1 according to the invention. A preheating device 2 is installed here upstream of a plasma source 3 with a downstream analyzer 4, following the primary sample apparatus 16. The preheating device 2 thus serves in this embodiment in heating the sample gas flow 5 with the sample aerosol 15.

[0123] It is possible to integrate the preheating device 2 as an independent module in a system according to the state of the art.

[0124] FIG. 5 depicts an exemplary second embodiment of a temperature control plasma source analyzer arrangement 1 according to the invention. In this embodiment, all three gas flows, thus sample gas flow 5, auxiliary gas flow 6 and cooler gas flow 7, are each equipped with a preheating device 2 prior to entering the plasma source 3.

[0125] Moreover, an exemplary depiction of various states over the process flow of an ICP-MS according to the prior art, thus without preheating device 2, is shown in FIG. 6, comprising a) temperature profile, b) sample aerosol evaporation, c) total ionization and d) diffusion loss.

[0126] FIG. 6a depicts the temperature profile between injection site 12 and extraction site 13 during the passage of the sample aerosol 15 through the plasma 14. According to the prior art, the injection temperature T.sub.IN corresponds to the start temperature T.sub.S. The start temperature T.sub.S is preferentially room temperature. The temperature reaches the extraction temperature T.sub.EX at the site of ion extraction 13.

[0127] FIG. 6b) shows a symbolic representation of the evaporation of the sample aerosol 15, depicted by the decreasing size of black circles representing the sample aerosol 15.

[0128] Looking at FIG. 6a) and FIG. 6b) simultaneously makes clear that the sample aerosol 15 continuously evaporates further as the temperature increases over the course of the process.

[0129] FIG. 6c) depicts the gradual increase of the ions generated from the sample aerosol 15 (total ionization) over the course of the process. Ionization is almost linear over the entire process of increasing the temperature in the plasma source 3.

[0130] In addition, FIG. 6d) depicts the gradual increase of ions lost by diffusion to outer plasma regions, which cannot be used for extraction (diffusion loss), over the course of the process.

[0131] A diffusion loss occurs throughout the entire process of increasing the temperature in the plasma source 3. As the process progresses, however, the diffusion loss no longer increases linearly but rather exponentially. Light ions are far more affected by radial diffusion into the surrounding plasma 14 than heavy ions.

[0132] The various states 6a) to 6d) over the course of the process are all related to one another.

[0133] FIG. 7 shows an exemplary depiction of various parameters over the course of the temperature-controlled gas flow-plasma source analysis method process according to the invention using a temperature control plasma source analyzer arrangement 1 for an aerosol heating application, comprising a) temperature profile, b) sample aerosol evaporation, c) total ionization and d) diffusion loss.

[0134] FIG. 7a depicts the temperature profile between start temperature T.sub.S and extraction temperature T.sub.EX. The preheating device 2 initially increases the start temperature T.sub.S to the injection temperature. T.sub.IN. T.sub.S<T.sub.IN applies. Thus, the sample aerosol 15 is introduced into the plasma 14 at the injection site 12 at the significantly higher temperature T.sub.IN instead of start temperature T.sub.S. There is a further increase in temperature in the plasma 14 to extraction temperature T.sub.EX. T.sub.S<T.sub.IN<T.sub.EX applies.

[0135] FIG. 7b) shows a symbolic representation of the evaporation of the sample aerosol 15, depicted by the decreasing size of black circles representing the sample aerosol 15.

[0136] Looking at FIG. 7a) and FIG. 7b) simultaneously makes clear that the sample aerosol 15 continuously evaporates as the temperature increases over the course of the process. The evaporation has already started in the preheating device 2 and steadily continues in the plasma source 3. As depicted here, given a sufficiently high enough T.sub.IN, initial aerosol evaporation can already occur within preheating device 2 due to the preheating effect.

[0137] In some embodiments, the preheating device 2 is configured to preheat the sample gas flow 5 of the plasma source 3 such that the sample gas flow 5 has, throughout an entire period of time between a start of an operation of the analyzer 4 and a stop of the operation of the analyzer 4, a constant injection temperature T.sub.IN at the injection site 12 where the sample gas flow 5 is introduced in the plasma source 3.

[0138] In this case, the preheating device 2 can be configured to preheat the sample gas flow 5 of the plasma source 3 such that the sample gas flow 5 has a constant injection temperature T.sub.IN at the injection site 12 which is higher than 200 C., in particular higher than 400 C., in some embodiments higher than 900 C., and up to 1100 C.

[0139] In some embodiments, the preheating device 2 is configured to preheat the sample gas flow 5 of the plasma source 3 such that the sample gas flow 5 has, preferably throughout the entire period between the start of the operation of the analyzer and the stop of operation of the analyzer 4, a variable injection temperature at the injection site 12 where the sample gas flow 5 is introduced into the plasma source 3, wherein the variable injection temperature varies, in particular oscillates, more particular oscillates sinusoidally, around and/or about a predetermined constant temperature value, preferably with a deflection or amplitude whose value is less than 5%, in particular less than 2.5%, more preferably less than 1.25% of the predetermined constant temperature value.

[0140] In this case, the preheating device 2 can be configured to preheat the sample gas flow 5 of the plasma source 3 such that the sample gas flow 5 has a variable injection temperature with a predetermined constant temperature value which is equal to or higher than 200 C., in some embodiments equal to or higher than 400 C., in some embodiments equal to or higher than 900 C., and up to 1100 C.

[0141] FIG. 7c) depicts the gradual increase of the ions generated from the sample aerosol 15 (total ionization) over the course of the process. Ionization is almost linear over the process of increasing the temperature in the plasma source 3. No ionization takes place in the preheating device 2.

[0142] Furthermore, FIG. 7d) depicts the gradual increase of ions lost by diffusion to outer plasma regions, which cannot be used for extraction (diffusion loss), over the course of the process. Light ions are much more strongly affected by radial diffusion into the surrounding plasma 14 than heavy ions.

[0143] A diffusion loss occurs as a result of the process of increasing the temperature in the plasma source 3. As the process progresses, however, the diffusion loss no longer increases linearly but exponentially. The preheating device 2 enables realizing a faster transfer of the sample aerosol 15, for example by means of a higher flow rate of the sample gas flow 5, which leads to a decrease in diffusion loss. No diffusion loss takes place in the preheating device 2.

[0144] The various states 7a) to 7d) over the course of the process are all related to one another.

[0145] The sample gas flow 5 is strongly preheated in the preheating device 2 prior to injection, which leads to a significant increase in the injection temperature T.sub.IN. Ideally, such a temperature is reached that part of the evaporation of the sample aerosol 15 has already taken place at the injection site 12. This thus thermally supports the further course of the process; only just a small difference between the injection temperature T.sub.IN and the extraction temperature T.sub.EX is required. The energy for the processes is now divided up, part of it already being supplied prior to injection into the plasma 14 and thus reducing the remaining amount of energy to be applied in the plasma. Lowering the amount of energy allows a reduction of the required residence time of the sample aerosol 15 in the plasma 14 (less energy needs to be transmitted at essentially the same power). This reduction in residence time thus allows an increased flow velocity/flow rate of the sample gas flow 5. The shortened residence time, or higher velocity of the pre-evaporated sample aerosol 15 respectively, reduces sample losses due to radial diffusion. A higher proportion of ions remains in the axial region of the plasma 14 and can be extracted (sampled). Due to the strong mass dependency of diffusion, the gain in usable ions is particularly high for the light ions. Yet heavy ions also show a reduction in diffusive losses, albeit to a lesser extent.

[0146] FIG. 8 shows a selection of possible variants of the design of the temperature control unit 21 able to be used in the preheating device 2, each in this example with regulation of the heating voltage 241 or respectively energy 242.

[0147] FIG. 8a) shows the direct heating of the gas transfer line 22 or a part thereof as heating line 211.

[0148] In FIG. 8b) a heating coil 212 located within the gas transfer line 22 is used.

[0149] It is also possible to use a heating filament 213 located within the gas transfer line 22 as shown in FIG. 8c).

[0150] FIG. 8d) shows a heating grid/heating braid 214 located within the gas transfer line 22.

[0151] In FIG. 8e), the heating of the gas transfer line 22 is realized by an external heating element 215.

[0152] The external excitation of a pre-plasma 216 as shown in FIG. 8f) constitutes a further possibility for heating the sample gas flow 5 within the gas transfer line 22.

[0153] A focused excitation of the sample gas flow 5 in the gas transfer line 22 by laser 217 as shown in FIG. 8g) is also possible.

[0154] The higher the achievable temperature during preheating of the sample gas flow 5, the shorter the achievable residence time of the sample aerosol 15 in the plasma 14. The shorter the residence time, the lower the diffuse losses of extractable ions and the element fractionation.

[0155] The overall yield of measurable ions is thus increased, wherein the light ions, which are otherwise most affected by loss, benefit disproportionately.

[0156] The stated control parameters in FIG. 8 are only intended for informational purposes. Controllable heating voltage can be equally replaced by a controllable heating current flow. Controllable heating energy can be equally replaced by a heating power, heating voltage or a heating current flow.

[0157] In the simplest case, an operator would set a fixed control parameter and feed the sample gas flow 5 into the plasma source 3 at the temperature resulting after thermal stabilization. The temperature reached by the sample gas flow 5 is not measured/controlled.

[0158] Additionally, measuring the temperature reached by the sample gas flow 5 may be desirable. To that end, the respective arrangement can be expanded by way of suitable temperature measuring elements. The temperature data thereby obtained can then be used to automatically regulate the heating parameter. In this regulated case, an operator can specify a target temperature and the preheating device 2 independently regulates the heating power by measuring the temperature and adjusting the control parameter in order to ensure a stable and defined heating process.

[0159] Inventive in the sense of this application is the use of sample gas flow/aerosol preheating in order to partially decouple the processes taking place in the plasma. This thereby achieves better and more complete usability of the sample aerosol employed and minimizes losses (through diffusion).

[0160] A further advantage of the arrangement and method according to the invention can be described. When the sample aerosol has already been for the most part pre-evaporated, or complete evaporation is at least supported later in the plasma, unevaporated sample residues will survive the transfer through the plasma to a significantly lesser extent. Since these would otherwise lead to deposits/encrustations on the sampler cone and skimmer cone, reducing/preventing unevaporated residues after plasma transfer is desirable. These encrustations would otherwise lead to a reduction in the aperture cross section, the material transfer would be reduced, and the number of usable ions would be reduced. The device must be switched off in this case and the apertures cleaned. The proposed method should thus also reduce the need for such service work.

[0161] The advantages that can be achieved with the inventive arrangement using the inventive method are thus summarized: [0162] lower element fractionation (increased matrix tolerance), [0163] lower mass fractionation (more stable measurement conditions, fewer data corrections), [0164] significantly increased ion yield (disproportionately for light ions) and [0165] reduced depositing of incompletely evaporated sample in the extraction unit (reduced amount of maintenance).

LIST OF REFERENCE NUMERALS

[0166] 1 temperature control plasma source analyzer arrangement [0167] 2 preheating [0168] 21 temperature control unit [0169] 211 heating line [0170] 212 heating coil [0171] 213 heating filament [0172] 214 heating grid/braid [0173] 215 external heating element [0174] 216 pre-plasma with external excitation [0175] 217 focused laser excitation [0176] 22 gas transfer line [0177] 23 insulating housing [0178] 24 control unit [0179] 241 heating voltage regulation [0180] 242 energy regulation [0181] 25 adapter for preheating sample gas flow feed [0182] 26 temperature control unit/control unit connecting cable [0183] 3 plasma source [0184] 31 adapter for plasma source sample gas flow feed [0185] 4 analyzer [0186] 5 sample gas flow [0187] 51 sample gas flow feed [0188] 6 auxiliary gas flow [0189] 61 auxiliary gas flow feed [0190] 7 cooling gas flow [0191] 71 cooling gas flow feed [0192] 8 plasma torch (quartz glass torch) [0193] 9 RF coil [0194] 10 sampler cone [0195] 11 skimmer cone [0196] 12 injection site of sample gas into plasma [0197] 13 ion extraction site from plasma [0198] 14 plasma [0199] 15 sample aerosol [0200] 16 primary sample apparatus