METHOD FOR SUPPLYING GAS FOR PLASMA BASED ANALYTICAL INSTRUMENT

Abstract

To achieve an effective gas filtering in a plasma spectrometric apparatus using a gas of a comparatively high consumption flow rate, and to improve the analytical ability, there is provided a plasma spectrometric apparatus containing a sample introducer for producing and delivering an injector gas containing an analyte sample, a plasma generator for generating plasma into which the injector gas is introduced, and an analyzer disposed subsequent to the plasma generator for analyzing the analyte sample. The plasma spectrometric apparatus contains a first gas line for supplying gas to the sample introducer, a second gas line for supplying gas to the plasma generator, and a filter located in the first gas line for removing impurities contained in the gas.

Claims

1. A plasma spectrometric apparatus comprising a sample introducer for producing and delivering an injector gas containing an analyte sample, a plasma generator for generating plasma into which the injector gas is introduced, and an analyzer disposed subsequent to the plasma generator for analyzing the analyte sample, wherein the plasma spectrometric apparatus further comprises: a first gas line for supplying gas to said sample introducer; a second gas line for supplying gas to said plasma generator; and a filter located in said first gas line for removing impurities contained in the gas.

2. The plasma spectrometric apparatus of claim 1, wherein said first gas line and said second gas line are branched from a source gas line.

3. The plasma spectrometric apparatus of claim 1, wherein the flow rate through said first gas line is smaller than the flow rate through said second gas line.

4. The plasma spectrometric apparatus of claim 1, wherein said filter is a gas purifier.

5. The plasma spectrometric apparatus of claim 1, wherein said first gas line branches into a third gas line and a fourth gas line, one delivering a carrier gas and the other delivering a make-up gas to said sample introducer.

6. The plasma spectrometric apparatus of claim 5, wherein said filter is located in each of said third gas line and said fourth gas line.

7. The plasma spectrometric apparatus of claim 1, wherein said second gas line branches into a fifth gas line and a sixth gas line, one delivering a plasma gas and the other delivering an auxiliary gas to said plasma generator.

8. The plasma spectrometric apparatus of claim 1, wherein a seventh gas line for delivering an auxiliary gas to said plasma generator is branched from said first gas line.

9. The plasma spectrometric apparatus of claim 1, wherein an eighth gas line for delivering a dilution gas to said sample introducer is branched from said first gas line.

10. The plasma spectrometric apparatus of claim 1, further comprising: an optional gas line for supplying an option gas to said sample introducer, and a second filter located in said optional gas line for removing impurities contained in the option gas, wherein said option gas is an oxygen-containing gas selected from the group consisting of oxygen, argon-containing oxygen, nitrogen-containing oxygen, helium-containing oxygen, and mixtures thereof.

11. The plasma spectrometric apparatus of claim 1, wherein the gas supplied through each of said first and said second gas lines is selected from the group consisting of argon, nitrogen, helium, hydrogen, and mixtures thereof.

12. The plasma spectrometric apparatus of claim 1, wherein said sample introducer comprises a nebulizer for producing said injector gas by mixing said analyte sample with the gas from said first gas line.

13. The plasma spectrometric apparatus of claim 1, wherein said injector gas is the output from a gas chromatograph.

14. The plasma spectrometric apparatus of claim 1, wherein said injector gas is the output from a laser ablation device.

15. The plasma spectrometric apparatus of claim 1, wherein said plasma generator comprises a plasma torch for receiving the gas from said second gas line to generate plasma into which the injector gas is introduced.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.

[0041] FIG. 1 is a schematic drawing showing a configuration example of an ICP-MS apparatus according to the present invention.

[0042] FIG. 2A is a schematic drawing showing an alternative configuration example of the ICP-MS apparatus shown in FIG. 1.

[0043] FIG. 2B is a schematic drawing showing an alternative configuration example of the ICP-MS apparatus shown in FIG. 1.

[0044] FIG. 3 is a schematic drawing showing a gas chromatograph which can be replaced with a sample introducer of the ICP-MS apparatus shown in FIG. 1.

[0045] FIG. 4 is a schematic drawing showing a laser ablation apparatus which can be replaced with a sample introducer of the ICP-MS apparatus shown in FIG. 1.

[0046] FIG. 5 is a graph showing a removing capability of a gas filter relative to a flow rate.

[0047] FIG. 6A is a graph showing a result of an analysis on successive chronological changes when not using a gas filter (not applying the present invention) in an ICP-MS apparatus.

[0048] FIG. 6B is a graph showing a result of an analysis on successive chronological changes when using a gas filter (applying the present invention) in an ICP-MS apparatus.

[0049] FIG. 6C is a bar graph showing the average values of the analysis results of FIGS. 6A and 6B (BEC value of Si).

[0050] FIG. 7 is a schematic drawing showing a configuration example of a conventional ICP-MS apparatus.

DETAILED DESCRIPTION

[0051] FIG. 1 shows, as an example of a plasma spectrometric apparatus according to the present invention, a configuration of an inductively coupled plasma mass spectrometer (ICP-MS apparatus) 100. In FIG. 1, an injector gas containing fine droplets of a liquid sample 21 is supplied to a plasma generator 30 from a sample introducer 20. Compounds and atoms existing in such fine droplets are decomposed and ionized in plasma 32. Sample ions obtained as a result are transferred to a mass analyzer 40. The mass analyzer 40 is configured such that the pressure is gradually decreased along the flow of the sample ions by using a turbo molecular pump, a rotary vacuum pump, and the like (not shown).

[0052] The sample ions are drawn to an ion lens system 43 through an orifice in an interface including a sampling cone 41 and a skimmer cone 42. Then, the sample ions are converged in a quadrupole mass spectrometer 45 through a collision/reaction cell 44. The quadrupole mass spectrometer 45 separates the sample ions based on a mass-to-charge ratio. As a device for separating the sample ions other than the quadrupole mass spectrometer, there also exist mass spectrometers of, for example, electric/magnetic sector type, flight time type, or ion trap type. The separated ions are measured by a detector 46. Such ICP-MS apparatus as the above provides means for performing a simultaneous multi-element analysis on most of the elements in the periodic table, and thus a mass spectrum can easily be obtained. In addition, such ICP-MS apparatus exhibits an excellent sensitivity such that element concentrations can be quantified at a level of one trillionth (ppt).

[0053] In FIG. 1, the mass analyzer 40 is illustrated as a mass analysis device using a quadrupole mass spectrometer. However, the mass analyzer 40 can also be an atomic emission spectrometer for observing emission spectrum of induced plasma generated in the plasma generator 30. The ICP spectrometric apparatus configured in this manner is generally referred to as an ICP-OES (Inductively Coupled Plasma—Optical Emission Spectrometry) apparatus or an ICP-AES (Inductively Coupled Plasma—Atomic Emission Spectrometry) apparatus.

[0054] In FIG. 1, a pressure-adjusted gas from a gas source 10 is supplied to a gas line 13 at a flow rate of from approximately 8 SLM to 27 SLM. The gas of the gas source is mainly an inert gas such as an argon (Ar) gas, nitrogen (N.sub.2) gas, and helium (He) gas, but can be a hydrogen (H2) gas, an oxygen (O.sub.2) gas, and the like, or a mixed gas thereof according to the usage. In FIG. 1, only one gas source is shown, but a plurality of gas sources can also be provided. In this case, the gas of each gas source can be the same or different.

[0055] The gas line 13 from the gas source 10 is referred to as a source gas line in the present specification, and is branched or divided into gas lines 61 and 63 through a connector 60. When a plurality of gas sources exist, the gas lines 61 and 63 can be respectively connected to each of the gas sources. The gas line 61 is connected to a gas filter 50. The gas filter 50 will be explained later. The gas flowing in the gas line 61 is removed of impurities contained therein by the gas filter 50, and is supplied to a gas line 62. The gas line 62 is, as is shown in FIG. 1, branched into a gas line 15 for a carrier gas and a gas line 16 for a make-up gas through a connector 64. A gas flow rate controller 14 is provided in each of the gas lines 15 and 16. The gas flow rate controller can be a mass flow controller (MFC).

[0056] The gas line 15 is connected to a nebulizer 22 in the sample introducer 20, and the gas line 16 is connected to an end cap 23. In addition, the liquid sample 21 containing an analyte is also supplied to the nebulizer 22. As shown, the nebulizer 22 is connected to a spray chamber 24 through the end cap 23. The nebulizer 22 mixes the carrier gas from the gas line 15 with the liquid sample 21, and sprays the mixture. The make-up gas passes through a surrounding of a tip of the nebulizer 22, assists the delivery of the nebulized sample, and optimizes the ionization condition of analysis object elements in the plasma. The nebulized sample is removed of large droplets by passing through the spray chamber 24 together with the carrier gas and the make-up gas, and is sent into an ICP torch 31 in the plasma generator 30 as the injector gas (aerosol).

[0057] The gas line 63 is branched into a gas line 17 for a plasma gas and a gas line 18 for an auxiliary gas through a connector 65. In the gas lines 17 and 18, a gas flow rate controller 14 is provided. The gas flow rate controller can be a mass flow controller (MFC). According to a command from a controller of the ICP analysis apparatus or a computer, etc. (not shown), each MFC 14 measures the mass flow rate of the gas flowing in each of the gas lines 15 to 18, and controls the flow rate.

[0058] The gas lines 13, 15 through 18, and 61 through 63 are each a tube made of, for example, a stainless steel or a resin, and the inner diameter of the tube is generally from about 0.5 mm to 8 mm in diameter. From the standpoint of eliminating an extremely trace amount of impurities, such as organic silicon compounds, organic sulfur compounds, or organic halogen compounds, a tube made of a stainless steel is more preferred. The ICP torch 31 which is also referred to as a plasma torch has a triple-tube structure of quartz, and has an inner tube to which the injector gas is introduced, an outer tube which is outside the inner tube, and an outermost tube which is further outside the outer tube. The auxiliary gas is introduced to the outer tube by the gas line 18, and the plasma gas is introduced to the outermost tube by the gas line 17.

[0059] At a tip of the ICP torch 31, a work coil (not shown) which provides an energy for generating the plasma 32 is disposed, and connected to a high frequency power source (not shown). With the auxiliary gas and the plasma gas being provided to the ICP torch 31, the high frequency power can be applied to make the plasma 32 in a lighting state. The temperature of the plasma reaches from a several 1,000 K to a 10,000 K. The plasma gas is used to generate and maintain plasma. In addition, the plasma gas also functions to cool down the ICP torch 31. The auxiliary gas plays a role of protecting the inner tube and the outer tube of the ICP torch 31 by shifting a position where the plasma 32 is generated toward a downstream side. Further, there is a case where the auxiliary gas does not need to be flown depending on the form of the plasma torch. The injector gas containing fine droplets of the liquid sample is provided from the inner tube. As described above, compounds and atoms existing in such fine droplets are decomposed and ionized in the plasma 32.

[0060] As described above, industrial gases supplied by gas providers may contain an extremely trace amount of impurities, or may be contaminated by piping, and the like. It is desirable that the gas used in particular for a plasma spectrometric apparatus such as an ICP-MS apparatus, an ICP-AES apparatus, a MIP-MS apparatus, and a MIP-AES apparatus does not contain impurities such as silicon (Si), sulfur (S), phosphorus (P), boron (B), krypton (Kr), xenon (Xe), chlorine (Cl), and bromine (Br). The above gas filter 50 is a gas purifier configured to remove such impurities.

[0061] For example, such gas purifier as the above has a cylindrical structure made of metal provided with an inlet for gas flowing in and an outlet for purified gas flowing out, and a purification element for purifying the gas is filled therein. As the purification element, for impurities of organic compounds such as organic silicon compounds, organic sulfur compounds, or organic halogen compounds, it is effective to use, for example, an absorbent such as activated carbon or zeolite, or an alloy called a getter, which is like a zirconium alloy that absorbs impurities in the gas. In addition, impurities such as hydrogen sulfide can be removed by causing a chemical reaction with a metal oxide such as a copper oxide. A gas purifier like this has a service life whose length significantly differs depending on the substance to be removed, but in general, it has an ability of continuously removing impurities from an argon gas of 99.999% purity flowing at 1 SLM for from 1000 to 100,000 hours.

[0062] Further, the gas filter 50 can be in a form of a cartridge. The gas filter 50 can be replaceably connected to the gas lines 61 and 62 by using a connector, and the like (not shown). In FIG. 1, one gas filter 50 is shown. However, as is indicated in the alternative configurations of FIG. 2A and FIG. 2B, gas filters 51 and 52 may also be provided in the gas line 15 for the carrier gas and the gas line 16 for the make-up gas, respectively. In FIG. 2A, the gas filters 51 and 52 are provided on the inlet side of the gas flow rate controller 14. However, the gas filters 51 and 52 may also be provided on the outlet side of the gas flow rate controller 14 as shown in FIG. 2B. In addition, in FIG. 1, FIG. 2A and FIG. 2B, one gas filter is provided in each gas line, but a plurality of gas filters can also be connected serially or in parallel in order to remove a wide variety of impurities.

[0063] FIG. 5 shows a result obtained experimentally on the capability of a gas purifier itself to remove a Si impurity in consideration of a case where the gas filter 50 is configured as a gas purifier. The horizontal axis of the graph indicates a flow rate (SLM) of the gas (including the Si impurity) flowing into the gas filter. The left vertical axis of the graph indicates a value obtained by converting a concentration of the Si impurity in the gas to a concentration in the sample solution. The right vertical axis of the graph indicates a passage rate at which the Si impurity passes through the gas filter without being removed. The curve A indicates a concentration of the Si impurity introduced into the gas filter in terms of a concentration in the sample. The curve B indicates a concentration of the Si impurity that passed through the gas filter in terms of a concentration in the sample. The curve C indicates a passage rate at which the Si impurity passes through the gas filter. The passage rate is obtained by dividing the value B by the value A.

[0064] It is obvious from FIG. 5 that the higher the flow rate of the gas flowing in, the more difficult to remove the Si impurity contained in the gas by the gas filter. For example, when comparing the leftmost point corresponding to the gas flow rate of 1 SLM with the rightmost point corresponding to the gas flow rate of 20 SLM in the graph C, the passage rate differs by approximately three digits. That is, the gas filter can effectively remove impurities when the gas flow rate is low (e.g., 1 SLM).

[0065] In the ICP-MS apparatus 100 shown in FIG. 1, the gas flow rate in the gas line 15 for the carrier gas is generally from approximately 0.2 to 1.5 SLM, preferably from approximately 0.5 to 1.0 SLM, and more suitably approximately 0.7 SLM. The gas flow rate in the gas line 16 for the make-up gas is from approximately 0.0 to 1.5 SLM, preferably from approximately 0.0 to 1.0 SLM, and more preferably approximately 0.3 SLM.

[0066] Further, the gas flow rate in the gas line 17 for the plasma gas is generally from approximately 8 to 23 SLM, and preferably from approximately 12 to 20 SLM. The gas flow rate in the gas line 18 for the auxiliary gas is generally from approximately 0.0 to 2.0 SLM, and preferably approximately 1 SLM. It is considered that the gas flow rate in the gas line 62 is approximately 1 SLM, and the gas flow rate in the gas line 63 is from approximately 13 to 21 SLM.

[0067] As described above, the gas filter can effectively remove impurities when the flow rate of the gas is low (e.g., 1 SLM). In addition, an analysis result of the plasma spectrometric apparatus is less affected by impurities contained in the plasma gas and the auxiliary gas than impurities contained in the injector gas. In the present invention, the gas filter 50 is used only in the gas line 62 having a low gas flow rate, and not used in the gas line 63 having a high gas flow rate. By such configuration, it is possible to effectively remove the impurities contained in the carrier gas and the make-up gas constituting the injector gas while effectively using the filtering capability of the gas filter 50. This also reduces background noise and the like attributed to the impurities, and improves the analytical ability of the plasma spectrometric apparatus. Further, it also prevents the life of the gas filter from being shortened.

[0068] In the above explanation, the gas filter 50 is used only in the gas line 62. However, if the gas flow rate in the gas line 18 for the auxiliary gas is low, the gas line 18 for the auxiliary gas may be branched or divided from the gas line 62 instead of the gas line 63. That is, in addition to the injector gas, the auxiliary gas may also be purified by the gas filter 50. This allows to further improve the analytical ability of the plasma spectrometric apparatus.

[0069] In the ICP-MS apparatus 100 as shown in FIG. 1, when the liquid sample 21 contains many substances that are not the analysis objects (e.g., sodium chloride, magnesium chloride, etc.) such as sea water, a dilution gas for diluting the injector gas may be supplied from a gas adding inlet 27. The dilution gas can be an argon gas, and supplied to the gas adding inlet 27 through a flow rate controller such as the flow rate controller 14 after being branched from the gas line 62. The flow rate of the dilution gas is from 0 to approximately 1 SLM, and preferably from approximately 0.3 to approximately 0.8 SLM.

[0070] In addition, when a solvent of the liquid sample 21 is an organic solvent, an oxygen-containing gas may also be added as an option gas from the gas adding inlet 27 to the injector gas. When the oxygen-containing gas is introduced as the option gas, decomposition of organic matters in the plasma 32 is accelerated and accumulation of undecomposed organic matters, soot, and the like to the torch 31, the sampling cone 41, the skimmer cone 42, and the ion lens system 43 can be inhibited, thereby preventing the analytical performance from being lowered. The option gas can be supplied to the gas adding inlet 27 from a different gas source (not shown) through a gas filter such as the gas filter 50. In the present specification, a gas line delivering the option gas is referred to as an optional gas line. A flow rate controller such as the flow rate controller 14 can also be provided in the optional gas line.

[0071] The option gas can be an oxygen gas, an argon-containing oxygen gas, a nitrogen-containing oxygen gas, a helium-containing oxygen gas, and mixtures thereof. The flow rate of the option gas is from 0 to approximately 1 SLM, and preferably from approximately 0.1 to approximately 0.5 SLM. In some cases, both the dilution gas and the option gas can be supplied to the gas adding inlet 27.

[0072] When the present invention is applied to a MIP analysis apparatus, the plasma generator 30 shown in FIG. 1 is replaced by a system generating microwave induced plasma (MIP), and the plasma gas and the auxiliary gas are supplied to the plasma generator 30 in the same manner as in the ICP analysis apparatus. A system generating MIP is, for example, explained in Patent Literature 3.

[0073] As an alternative of the ICP-MS apparatus 100 of FIG. 1, the sample introducer 20 of FIG. 1 can be replaced by a gas chromatograph 300 shown in FIG. 3. In this case, the carrier gas or the make-up gas in the gas chromatograph can be supplied from a different gas source (not shown). A gas filter such as the gas filter 50 shown in FIG. 1 can be provided in a gas line for the carrier gas or the make-up gas from the different gas source, and can purify the carrier gas or the make-up gas.

[0074] The carrier gas in the gas chromatograph can generally be a helium (He) gas, an argon (Ar) gas, a hydrogen (H2) gas, a nitrogen (N2) gas, and the like. As an alternative, the carrier gas in the gas chromatograph 300 may be supplied through a gas line 15′ as the gas line 15 shown in FIG. 1. In addition, the make-up gas in the gas chromatograph 300 can be supplied through a gas line 16′ as the gas line 16 shown in FIG. 1. The make-up gas is a gas for achieving an optimum ionization condition in detecting an analyte element in the mass analyzer 40, and the range of the flow rate is the same as that of the carrier gas or the make-up gas used in a normal ICP analysis apparatus. Therefore, in an aspect in which the carrier gas is supplied using a different gas source, the make-up gas for the gas chromatograph 300 can be supplied through the gas line 15 or the gas line 16 as shown in FIG. 1. As is shown in FIG. 3, an output of the gas chromatograph 300 is connected to an injector 314 through a transfer line 313, and the injector 314 is inserted in a plasma torch 31′ as an inner tube.

[0075] In FIG. 3, a sample 21′ is introduced to a column 310 together with the carrier gas in the gas line 15′. The introduced sample is separated by each component when passing through the column 310. The make-up gas supplied through the gas line 16′ passes through a preheating tube 311, which adjusts the temperature of the make-up gas. The carrier gas containing the sample separated by the column 310 and the temperature-adjusted make-up gas are mixed to produce the injector gas. The injector gas is introduced to the inner tube of the plasma torch 31′ as shown in FIG. 1 through the transfer line 313 and the injector 314. The temperatures of the column 310 and the preheating tube 311 are adjusted by an oven. Further, the temperatures of the transfer line 313 and the injector 314 are adjusted by a heater and the like (not shown).

[0076] As yet another alternative, the sample introducer 20 of FIG. 1 can be replaced by a laser ablation device 400 shown in FIG. 4. In this case, the gas lines 15 and 16 of FIG. 1 are connected to gas lines 15″ and 16″ shown in FIG. 4, respectively. In addition, the portion A shown in FIG. 1 and the portion A shown in FIG. 4 are connected. In FIG. 4, a solid sample 420 is placed in an ablation cell 410. A laser light from a laser 450 is irradiated to the surface of the solid sample 420 thorough a half mirror 440 and a lens and the like (not shown). By a CCD camera 430, portions to be analyzed in the sample can be observed. The sample evaporated and particulated by the irradiated laser light is discharged from the ablation cell 410 by the carrier gas, but in some cases, gas such as a helium (He) gas is added to the carrier gas for the purpose of optimizing the ablation condition of the sample. Then, the discharged sample is mixed with the make-up gas to become the injector gas. The injector gas is introduced to the inner tube of the plasma torch 31 shown in FIG. 1.

EXAMPLES

[0077] The impact on an analysis result by applying the present invention in an ICP-MS apparatus was experimentally verified. In the present experiment, an ICP-MS/MS apparatus such as that described in Patent Literature 4 was used in a gas supplying configuration shown in FIG. 1. In this case, a chamber was extended such that a quadrupole mass filter could be disposed between the ion lens system 43 and the collision/reaction cell 44 in the mass analyzer 40 of FIG. 1. In addition, in the ICP-MS/MS apparatus used in the experiment, a collision/reaction cell provided with an octupole was used.

[0078] The condition of the experiment was as follows. For gas as a gas source, an argon gas of 99.999% purity commercially available from Taiyo Nippon Sanso Corporation as an industrial gas was used. Then, the argon gas was used each as a plasma gas, an auxiliary gas, a carrier gas, and a make-up gas, having the flow rate of 15.0 SLM, 0.90 SLM, 0.70 SLM, and 0.37 SLM, respectively. For a gas filter, RMSH-2 commercially available from Agilent Technologies was used. As a high frequency power for generating plasma, a power of 1500 W was applied to the work coil. The introduction speed of the sample solution was approximately 200 μL/min (0.2 g/min), and the temperature of the spray chamber was 2° C. In addition, the distance between the downstream end of the work coil to the tip of the sampling cone was 4 mm. As a cell gas, a helium (He) gas was introduced at a flow rate of 1 SCCM, and a 10% ammonia (10%NH3/He) gas diluted by helium was introduced at a flow rate of 0.5 SCCM to the collision/reaction cell. Along the flow of sample ions, the mass-to-charge ratio (m/z) for passing through the first quadrupole mass filter was set to 28, and the m/z for passing through the second quadrupole mass filter was set to 44, and the ICP-MS/MS apparatus was operated as MS/MS mode. In this mode, after a Si ion (Si.sup.+, m/z=28) generated in the plasma passes through the first quadrupole mass filter, it collides and reacts with an ammonia molecule in the collision/reaction cell provided with the octopole, and becomes SiNH.sub.2.sup.+(m/z=44), which then reaches to a detector and is converted to an electric signal after passing through the second quadrupole mass filter.

[0079] The experiment results are shown in FIG. 6A through FIG. 6C. FIG. 6A shows a background equivalent concentration (BEC) and a signal intensity of a Si element when continuously operating, without using the gas filter 50 as in the conventional ICP-MS apparatus shown in FIG. 7, such ICP-MS apparatus for 36 hours. In this graph, the horizontal axis indicates the time (h), the left vertical axis the signal intensity, and the right vertical axis the BEC. The graph of FIG. 6B shows a BEC and a signal intensity of a Si element when continuously operating, by using the gas filter 50 as in the ICP-MS apparatus of FIG. 1, the ICP-MS apparatus for 36 hours based on the same condition as that of FIG. 6A. The horizontal axes of the graphs in FIG. 6A and FIG. 6B and the vertical axes thereof are in the same range, respectively.

[0080] In the graphs of FIG. 6A and FIG. 6B, graph (1) shows a signal intensity (the signal intensity of the background) (counts/sec) when ultrapure water (deionized water, or DIW) is introduced, and graph (2) shows a signal intensity (counts/sec) when a sample containing Si of 1 ppb (1 μg/L) is introduced into ultrapure water. Here, by subtracting (1) from (2), a net signal intensity relative to Si per 1 ppb, that is, apparatus sensitivity (counts/(sec.Math.ppb)), can be obtained. Graph (3) can be obtained by dividing the signal intensity (1) of the background at the time of introducing ultrapure water by the apparatus sensitivity ((2)-(1)). The value shown by graph (3) indicates a background signal intensity as a concentration in a solution (ppb), and is referred to as a BEC (background equivalent concentration). The BEC value is a numerical value serving as a reference for at how low a level an analysis can be conducted in an analytical apparatus, and the smaller the value is, the lower the concentration level at which the analysis is possible.

[0081] The graph of FIG. 6A indicates that the background changes over time, showing fluctuations in a range between several 100 ppt and several 10 ppb in terms of BEC. Such changes are considered to be caused by the changes in the temperature of the piping or the flow rate of the gas flowing therein, the industrial gas lot, or the individual difference in a compressed gas cylinder contamination. Under this condition, it is possible to detect and quantify Si in a concentration range of several 100 ppb; however, it is not possible to conduct an analysis at a level of several 10 ppb, let alone an analysis at a level of ppb. On the other hand, in the graph of FIG. 6B, unlike the graph of FIG. 6A, the BEC value is stable over approximately 36 hours, and the BEC value of Si is restrained so as to be equal to or less than several 100 ppt. Thus, it is made possible to detect and quantify Si in a concentration range lower than the level of several ppt.

[0082] The average of BEC values of Si shown in FIG. 6A and FIG. 6B are 2.97 ppb and 0.32 ppb. FIG. 6C shows these average values in a bar graph. BEC represents a concentration of a measurement object element that gives a signal intensity equivalent to the background intensity. In other words, lowering of a BEC value signifies a reduction in the background noise attributed to impurities. Therefore, it was verified that removing of impurities contained in the carrier gas and the make-up gas by the gas filter 50 according to the present invention reduced, in a continuous 36-hour operation, the fluctuation in the background level and the background noise.

[0083] Below shows exemplary embodiments comprising combinations of various configuration requirements of the present invention.

[0084] 1. A plasma spectrometric apparatus comprising a sample introducer for producing and delivering an injector gas containing an analyte sample, a plasma generator for generating plasma into which the injector gas is introduced, and an analyzer disposed subsequent to the plasma generator for analyzing the analyte sample, wherein the plasma spectrometric apparatus further comprises: a first gas line for supplying gas to said sample introducer; a second gas line for supplying gas to said plasma generator; and a filter located in said first gas line for removing impurities contained in the gas.

[0085] 2. The plasma spectrometric apparatus according to the above 1, wherein said first gas line and said second gas line are branched from a source gas line.

[0086] 3. The plasma spectrometric apparatus according to the above 1 or 2, wherein the flow rate through said first gas line is smaller than the flow rate through said second gas line.

[0087] 4. The plasma spectrometric apparatus according to any one of the above 1 to 3, wherein said filter is a gas purifier.

[0088] 5. The plasma spectrometric apparatus according to any one of the above 1 to 4, wherein said first gas line is provided with a gas flow rate controller between said sample introducer and said filter.

[0089] 6. The plasma spectrometric apparatus according to any one of the above 1 to 5, wherein said first gas line branches into a third gas line and a fourth gas line, one delivering a carrier gas and the other delivering a make-up gas to said sample introducer.

[0090] 7. The plasma spectrometric apparatus according to the above 6, wherein said filter is located in each of said third gas line and said fourth gas line.

[0091] 8. The plasma spectrometric apparatus according to any one of the above 1 to 7, wherein said second gas line branches into a fifth gas line and a sixth gas line, one delivering a plasma gas and the other delivering an auxiliary gas to said plasma generator.

[0092] 9. The plasma spectrometric apparatus according to any one of the above 1 to 7, wherein a seventh gas line for delivering an auxiliary gas to said plasma generator is branched from said first gas line.

[0093] 10. The plasma spectrometric apparatus according to any one of the above 1 to 9, wherein an eighth gas line for delivering a dilution gas to said sample introducer is branched from said first gas line.

[0094] 11. The plasma spectrometric apparatus according to any one of the above 1 to 10, further comprising: an optional gas line for supplying an option gas to said sample introducer, and a second filter located in said optional gas line for removing impurities contained in the option gas.

[0095] 12. The plasma spectrometric apparatus according to any one of the above 1 to 11, wherein the gas supplied through each of said first and said second gas lines is selected from the group consisting of argon, nitrogen, helium, hydrogen, and mixtures thereof.

[0096] 13. The plasma spectrometric apparatus according to the above 11, wherein said option gas is an oxygen-containing gas selected from the group consisting of oxygen, argon-containing oxygen, nitrogen-containing oxygen, helium-containing oxygen, and mixtures thereof.

[0097] 14. The plasma spectrometric apparatus according to any one of the above 1 to 13, wherein said sample introducer comprises a nebulizer for producing said injector gas by mixing said analyte sample with the gas from said first gas line.

[0098] 15. The plasma spectrometric apparatus according to any one of the above 1 to 13, wherein said injector gas is the output from a gas chromatograph.

[0099] 16. The plasma spectrometric apparatus according to any one of the above 1 to 5, wherein, said injector gas is the output from a gas chromatograph, said first gas line delivers one of a carrier gas and a make-up gas to the gas chromatograph, the other gas is delivered to the gas chromatograph through a further gas line, and a further filter is provided in the further gas line for removing impurities from the other gas.

[0100] 17. The plasma spectrometric apparatus according to any one of the above 1 to 13, wherein said injector gas is the output from a laser ablation device.

[0101] 18. The plasma spectrometric apparatus according to any one of the above 1 to 17, wherein said plasma generator comprises a plasma torch for receiving the gas from said second gas line to generate plasma into which the injector gas is introduced.

[0102] 19. The plasma spectrometric apparatus according to any one of the above 1 to 18, wherein said plasma generator uses inductively coupled plasma or microwave induced plasma.

[0103] 20. The plasma spectrometric apparatus according to any one of the above 1 to 19, wherein said analyzer uses a mass spectrometer or an atomic emission spectrometer.

[0104] 21. In a plasma spectrometric apparatus comprising a sample introducer for producing and delivering an injector gas containing an analyte sample, a plasma generator for generating plasma into which the injector gas is introduced, and an analyzer disposed subsequent to the plasma generator for analyzing the analyte sample, a method for reducing background intensity in measurements, comprising: supplying a first gas to said sample introducer through a filter for removing impurities; and supplying a second gas to said plasma generator without filtering.

[0105] 22. The method according to the above 21,wherein the flow rate of said first gas is smaller than the flow rate of said second gas.

[0106] 23. The method according to the above 21 or 22, wherein said first gas is used as a carrier gas and a make-up gas.

[0107] 24. The method according to any one of the above 21 to 23, wherein said second gas is used as a plasma gas and an auxiliary gas.

[0108] 25. The method according to the above 21 or 22, wherein said first gas is used as a carrier gas, a make-up gas, and an auxiliary gas.

[0109] 26. The method according to the above 21 or 22, wherein said first gas is used as a carrier gas, a make-up gas, and a dilution gas.

[0110] 27. The method according to any one of the above 21 to 26, wherein said first gas and said second gas are supplied from the same gas source.

[0111] 28. The method according to any one of the above 21 to 27, wherein said filter is a gas purifier.

[0112] 29. The method according to the above 21, further comprising supplying an option gas to said sample introducer through a second filter for removing impurities.

[0113] 30. The method according to any one of the above 21 to 29, wherein said plasma generator uses inductively coupled plasma or microwave induced plasma.

[0114] 31. The method according to any one of the above 21 to 30, wherein said analyzer uses a mass spectrometer or an atomic emission spectrometer.

EXPLANATION OF REFERENCE NUMERALS

[0115] 10: Gas source

[0116] 13, 15, 15′, 15″, 16′, 16″, 17, 18, 61 to 63: Gas line

[0117] 14: Gas flow rate controller

[0118] 20: Sample introducer

[0119] 21, 21′: Sample

[0120] 22: Nebulizer

[0121] 30: Plasma generator

[0122] 31, 31′: Plasma torch

[0123] 40: Mass analyzer

[0124] 50, 51, 52: Gas filter

[0125] 100, 100′: ICP-MS apparatus

[0126] 300: Gas chromatograph

[0127] 400: Laser ablation device

[0128] It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.