A sample device and sample testing method for glow discharge mass spectrometer

Abstract

The present invention provides a sample device for a glow discharge mass spectrometer, comprising a second cathode sample injection device, wherein the second cathode sample injection device comprises a shell having an opening, a hollow metal sheet and a spring insert, wherein the hollow metal sheet has a hollow pattern and is fixed to the opening of the shell, and the spring insert is fixed inside the shell and is in a compressed state, and a sample is clamped between the hollow metal sheet and the spring insert. The present invention also provides a method for testing a glow discharge mass spectrometer using the sample device as described above. The sample device for a glow discharge mass spectrometer of the present invention is applicable to all existing GD-MS instruments, and samples of various sizes suitable for the sample can be directly placed behind the hollow second cathode for analysis.

Description

Technical Field

[0001] The invention belongs to the technical field of glow discharge mass spectrometers, and in particular relates to a sample device for a glow discharge mass spectrometer and a method for performing sample testing using the glow discharge mass spectrometer equipped with the sample device. Background Art

[0002] Glow discharge mass spectrometry (GD-MS) uses glow discharge ionization to generate ions for analysis of samples, and then uses mass spectrometry to detect these ions to achieve qualitative and quantitative analysis of the elemental composition of the samples. GD-MS has the advantages of direct measurement, high sensitivity, low detection limit, small matrix effect, many analyzable elements, simultaneous measurement of multiple elements, and wide linear dynamic range. These characteristics make it an important means for the detection of purity and trace impurities of solid materials, especially high-purity inorganic materials. In glow discharge, a large number of particles with representative composition can be obtained from solid samples through cathode sputtering, which is the key to glow discharge for analyzing elemental composition. At present, commercial GD-MS mostly uses a DC discharge source, and the sample is directly used as the cathode of the glow discharge, and the sample is usually required to have a certain conductivity. In actual production, processing and use, non-conductor materials often account for the vast majority, and the material has a variety of forms, including solid blocks, powders, granules, chips, and rods. For bulk conductors and semiconductors such as most metals, alloys, and high-purity silicon, the samples only need to be simply cut into a suitable shape (needle-shaped 20mm×2mm×2mm or sheet-shaped 20mm×20mm×2mm), and then directly analyzed after surface cleaning. For conductive samples with inappropriate shapes and sizes, such as powders and granules, the samples can be made into a suitable shape for GD-MS analysis through processing methods such as tableting and grafting.

[0003] For non-conductive powder samples, auxiliary electrodes are required or the sample is properly mixed with conductive materials (such as silver powder and copper powder) to prepare it into a suitable size for analysis. The current general processing method for non-conductive samples is to heat and melt the low-melting-point conductive metal indium and wrap it on the surface of the needle-shaped sample, using the conductivity of indium to assist the sample to conduct electricity, or using a high-purity tantalum bath as an auxiliary metal to analyze bulk samples, or using the grafting method to analyze small-sized samples. However, these sample preparation methods have certain problems: the metal indium used in the sample preparation process has a low melting point and needs to be cooled and discharged. It is easy to melt during a long discharge process, resulting in test failure, and because it cannot be reused, it increases the detection cost. The tantalum bath method used can avoid the cumbersome pre-treatment of small-sized samples, but the tantalum bath causes the sample to have a reduced measurable area, resulting in a decrease in signal intensity and a poor detection limit, which cannot give full play to the advantages of the GD-MS method. At the same time, the sample is easy to fall off from the opening of the tantalum bath during the push-pull process of the injection rod, which seriously affects the detection speed.

[0004] Therefore, a sample device for samples of various sizes is needed for measurement by a glow discharge mass spectrometer. Summary of the invention

[0005] In view of the limitations of the prior art, the present invention aims to provide a sample device for measuring non-conductor powders using a glow discharge mass spectrometer and a method for performing sample testing using a glow discharge mass spectrometer equipped with the sample device, so as to solve the problem of analyzing samples of different types and sizes using the glow discharge mass spectrometry (GD-MS) method.

[0006] In a first aspect, the present invention provides a sample device for a glow discharge mass spectrometer, comprising a second cathode sample injection device, wherein the second cathode sample injection device comprises a shell having an opening, a hollow metal sheet and a spring insert, wherein the hollow metal sheet has a hollow pattern and is fixed on the opening of the shell, and the spring insert is fixed inside the shell and is in a compressed state, and the sample is clamped between the hollow metal sheet and the spring insert.

[0007] According to the present invention, the sample device for glow discharge mass spectrometer of the present invention has a simple structure. By adopting the sample device of the present invention, under the premise of meeting the analysis of conventional size samples, the GD-MS can analyze and test samples of different sizes and shapes by designing and manufacturing opening shapes of different specifications, so that the GD-MS has the function of being able to quickly and efficiently analyze samples of various sizes. The modified GD-MS sample injection device can be used for the analysis of standard size samples as well as for the analysis of irregular size samples, which can effectively broaden the size range of samples that can be analyzed by GD-MS, improve the analysis speed while improving the sample signal strength, and reduce the detection cost.

[0008] Preferably, the shell is provided with a groove at the open portion for fixing the hollow metal sheet.

[0009] Preferably, the hollow metal sheet is aluminum, copper, tantalum, gold, platinum, or tungsten.

[0010] According to the present invention, the hollow second cathode metal sheet used for glow discharge mass spectrometry analysis is made of a high-purity metal sheet. The use of a high-purity metal sheet can effectively reduce the interference of impurity elements contained in the metal sheet itself. Among them, aluminum, copper, tantalum, gold, platinum, or tungsten sheets have good conductivity. In the glow discharge, the hollow second cathode acts as an electric cathode to participate in the discharge and produce sputtering. Some metal atoms produced by sputtering will be re-deposited on the surface of the sample to form a thin conductive layer, thereby causing the sputtering of the sample. When the conductivity of the sample itself is poor, the selection of a metal sheet with good conductivity is more conducive to promoting the sputtering of the sample.

[0011] Preferably, the volume of the second cathode sample feeding device is smaller than the volume of the glow discharge cell so that it can be placed in the glow discharge cell.

[0012] In a second aspect, the present invention further provides a method for performing glow discharge mass spectrometer testing using the sample device as described above, comprising the following steps:

[0013] The sample to be tested and the hollow metal sheet are respectively cleaned with dilute acid, ultrapure water and anhydrous ethanol in advance, and dried;

[0014] Loading the cleaned sample into the second cathode sample introduction device;

[0015] The second cathode sample introduction device containing the sample is evacuated and then sent into the glow discharge cell of the glow discharge mass spectrometer;

[0016] Connect the DC source and adjust the appropriate discharge pressure, discharge current and voltage for discharge;

[0017] The elements to be measured in the sample are scanned and the signal intensity is recorded.

[0018] Preferably, the samples include crystals of various sizes, ceramics, glass or other conductive, semi-conductive and non-conductive materials.

[0019] Preferably, when cleaning the sample, the sample is first ultrasonically cleaned in dilute nitric acid, then ultrasonically cleaned twice in ultrapure water, and finally cleaned with anhydrous ethanol and dried.

[0020] Preferably, the display mode of the signal strength is a current mode or a voltage mode.

[0021] Beneficial effects of the present invention:

[0022] The sample device for glow discharge mass spectrometer of the present invention is applicable to all existing GD-MS instruments and can directly place samples of various sizes behind the hollowed-out second cathode for analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a hollow second cathode sample introduction device for a glow discharge mass spectrometer according to the present invention;

[0024] Figure 2 It is a structural schematic diagram of a sheet structure sample pool involved in the present invention;

[0025] Figure 3 Taking a high-purity tantalum sheet as an example, a schematic diagram of a hollow second cathode sample introduction device for processing the tantalum sheet into three types of W-shaped openings is shown;

[0026] Figure 4 Taking a high-purity tantalum sheet as an example, a schematic diagram of a hollow second cathode sample introduction device for processing the tantalum sheet into S, I, C, C, A, S opening styles;

[0027] Figure 5Taking a high-purity tantalum sheet as an example, a schematic diagram of a tantalum sheet processed into a mesh-shaped and O-shaped hollow second cathode sample introduction device;

[0028] Figure 6 The change of matrix element signal intensity with sputtering time when using GD-MS indium sheet, caged tantalum tank and hollow second cathode sampling device (taking high purity tantalum sheet as an example, W opening style) to test Al2O3 sample;

[0029] Figure 7 The change of matrix element signal intensity with sputtering time when using GD-MS three sizes of hollow second cathode sampling devices (taking high-purity tantalum sheet as an example, W opening style) to test SiC samples. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings and the following embodiments. It should be understood that the accompanying drawings and the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0031] <Hollowed-out second cathode sample introduction device>

[0032] like Figure 1 The present invention is a schematic diagram of the structure of a hollow second cathode sample introduction device for a glow discharge mass spectrometer. Figure 1 As shown, the sample device for a glow discharge mass spectrometer of the present invention comprises a second cathode sample injection device 1, wherein the second cathode sample injection device 1 comprises a metal box 11 with an opening, a hollow metal sheet 12 and a spring insert 13, wherein the hollow metal sheet 12 has a hollow pattern and is fixed on the opening of the metal box 11, and the spring insert 13 is fixed inside the metal box 11 and is in a compressed state, and the sample A is clamped between the hollow metal sheet 12 and the spring insert 13. In one embodiment, the metal box 11 is provided with a groove 14 at the opening for fixing the hollow metal sheet 12.

[0033] The hollow metal sheet used for glow discharge mass spectrometry analysis in the present invention is prepared by punching a high-purity metal sheet, which can effectively reduce the interference of impurity elements contained in the metal sheet itself on the elements to be measured. Metals with good conductivity such as aluminum, copper, tantalum, gold, platinum or tungsten are preferred. In addition, different metals contain different types of impurities, so the metal sheet should also be selected according to the type of test elements of the sample to be measured. After punching holes in the metal sheet, it is processed into a hollow second cathode injection device of different sizes and shapes. The shape and size of the holes on the hollow metal sheet should be determined according to the specific shape and size of the sample, so it is necessary to design a hole structure that adapts to the size of various types of samples. The hollow second cathode injection device finally prepared should have a size smaller than the glow discharge size. Taking the Autoconcept GD90 GD-MS as an example, the inner diameter of the cathode discharge cell is 42mm, so it is necessary to set an appropriate injection device size so that the volume of the hollow second cathode is smaller than the volume of the discharge cell and can be placed in the discharge cell.

[0034] In the present invention, in view of the cumbersome sample preparation process in the existing GD-MS analysis of samples of different types and sizes, a hollow second cathode sample introduction device is selected to realize direct GD-MS sample introduction analysis and prevent samples from falling off.

[0035] The preparation of the hollow second cathode sample introduction device of the present invention comprises the following steps:

[0036] a) using a high-purity metal sheet as a hollow second cathode, the outer diameter of the high-purity metal sheet is, for example, 31.8 mm, and the thickness is, for example, 0.25 mm, and opening holes of different shapes on the high-purity metal sheet to facilitate stable discharge sputtering;

[0037] b) The hollow second cathode consists of a high-purity hollow metal sheet and a metal box. The dimensions of the metal box are outer diameter 35 mm × thickness 5.8 mm × middle spring insert (fixed sample) height 4 mm, inner diameter 30.4 mm, and groove diameter 32 mm.

[0038] <Sample Pool>

[0039] like Figure 2 FIG. 1 is a schematic diagram of the structure of the sheet structure sample pool of the present invention. Figure 2 As shown, the sheet-like structure sample cell of the present invention comprises a fixed groove 2 and an anode disk 3, a ceramic gasket 4 and a hollow second cathode sample introduction device 1 located in the fixed groove 2.

[0040] The sample cell is installed in a glow discharge mass spectrometer and is applicable to all glow discharge mass spectrometers, including the existing VG9000 high-resolution glow discharge mass spectrometer, Element GD, Autoconcept GD90 and AstruM high-resolution glow discharge mass spectrometers.

[0041] The hollow second cathode sample introduction device for the existing GD-MS instrument provided by the present invention can directly place samples of various shapes and sizes in a metal box for analysis. For powder samples, the sample introduction device can save sample preparation time, and the direct tableting method or the boric acid tableting method can be used for direct sample introduction. For other block, sheet or granular samples, the hollow second cathode sample introduction device can not only prevent the sample from falling off, but also increase the signal strength through metal-assisted sputtering.

[0042] On the other hand, the present invention also provides a method for testing a non-conductor sample using the hollow second cathode sample introduction device, comprising the following steps:

[0043] a) The sample to be tested and the hollow metal sheet are respectively cleaned with dilute acid, ultrapure water and anhydrous ethanol in advance, and dried;

[0044] b) placing the sample into the hollowed-out second cathode metal box;

[0045] c) evacuating the hollowed-out second cathode sample introduction device and the sample assembly and placing them into the GD-MS sheet discharge cell;

[0046] d) Connect a DC source and adjust the appropriate discharge pressure, discharge current and voltage for discharge;

[0047] e) Scan the sample for the element to be tested and record the signal intensity.

[0048] In more detail, samples prepared for analysis using this method include: crystals, ceramics, glass or other conductive, semi-conductive and non-conductive materials;

[0049] When cleaning the sample, the sample is usually ultrasonically cleaned in dilute nitric acid (preferably in a ratio of 1:1), then ultrasonically cleaned twice in ultrapure water, and finally washed with ethanol and dried;

[0050] Pick up the cleaned sample with tweezers and place it in a metal box. After the sample is installed, use the spring insert in the metal box to support the sample so that it is located between the hollow metal sheet and the metal box. The sample must completely cover the hollow holes and snap the hollow metal sheet into the groove of the metal box.

[0051] The experimental conditions selected by this method are determined by the specific range of the GD-MS model used. Taking the Autoconcept GD90 GD-MS as an example, the optional experimental conditions are 0.8-3.5 kV discharge voltage, 0.5-4.0 mA discharge current and 0.5-2.0 cc / min argon gas flow rate.

[0052] The signal strength display mode selected by this method is current mode or voltage mode.

[0053] The glow discharge mass spectrometer containing the hollow second cathode sample introduction device of the present invention has the following advantages when analyzing samples:

[0054] The sample pretreatment is simple and solid sample can be directly injected;

[0055] Compared with the second cathode sample introduction device, the hollowed-out second cathode can prevent the sample from falling off, thereby increasing the sample signal strength and shortening the detection cycle;

[0056] The modified sample injection device can be used for the analysis of samples of standard size as well as samples of different sizes, which can effectively broaden the range of sample sizes that can be analyzed by GD-MS;

[0057] It has strong universality and wide application range.

[0058] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description of this article, and are not necessarily limited to the specific values ​​​​exemplified below.

[0059] In the following embodiments, Autoconcept GD90 GD-MS is selected, and a high-purity tantalum sheet with a purity of >99.9995% is used as the hollow metal sheet. The high-purity tantalum has an outer diameter of 31.8 mm and a thickness of 0.25 mm. Apertures of different shapes and shapes are opened on the high-purity tantalum to adapt to samples of various shapes and sizes and obtain stable discharge sputtering.

[0060] The punched high-purity tantalum sheet is processed into sputtering surfaces of different sizes and shapes. The high-purity tantalum as the hollow second cathode consists of a high-purity hollow tantalum cover and a metal box. The metal box is made of brass. The size of the brass box part is 35mm in outer diameter × 5.8mm in thickness, 30.4mm in inner diameter, 32mm in groove diameter, and 4mm in height of the middle spring insert (iron) (fixed sample). Taking high-purity tantalum as an example, the tantalum sheet is processed into 7 shapes (including but not limited to W, S, I, C, A, O, mesh style) ( Figure 3 , Figure 4 , Figure 5 ) of the hollow second cathode sampling device, and the signal intensity of typical elements detected when glow discharge mass spectrometer analysis is performed using hollow tantalum surfaces of different shapes. The greater the signal intensity, the better the hollow second cathode sampling device.

[0061] Among the many areas formed by glow discharge, there are two areas that are important for sample analysis, namely the "negative glow area" and the "cathode dark area". The cathode dark area is a thin layer area close to the cathode surface with a higher positive ion density. The voltage drop of the entire glow discharge is almost entirely added to this area. Under the action of the electric field, positive ions accelerate toward the cathode, bombard the cathode, and sputter out the cathode material. Therefore, the size of the hollow second cathode as the cathode discharge area is crucial. Its area is composed of the sample area and the tantalum sheet area, that is, when the cathode discharge area is constant, increasing the sample contact area will reduce the tantalum sheet contact area. If the sample area is too large, the equivalent capacitance of the discharge area will be too large, and if it is too small, the sample matrix signal will be reduced. The hollow tantalum surface plays the role of auxiliary discharge and also requires a suitable sputtering area. Therefore, it is necessary to study the appropriate opening area size parameters to obtain the best sample signal strength and stability. Taking the W opening shape as an example, we designed three specifications of W opening shapes (large, medium, and small) of hollow tantalum sheets, such as Figure 3 shown.

[0062] Embodiment 1:

[0063] The hollow second cathode sampling device and sheet Al2O3 were ultrasonically cleaned in a mixed solution of nitric acid (HNO3) and ultrapure water in a ratio of 1:1, then ultrasonically cleaned twice in ultrapure water, and finally washed with anhydrous ethanol and dried. The cleaned sample was loaded into the hollow second cathode sampling device, and after vacuuming, the combination was loaded into the GD-MS sample cell for analysis. The optimized discharge voltage was 2.2kV, the discharge current was 1.1mA, and the discharge gas (Ar) flow rate was 1.0cc / min. Then, the element signal intensity in the sample was measured over time to further characterize the stability of the method. At the same time, the cage tantalum trough method and the indium sheet method were used to test the GD-MS signal intensity of the same sample as the control group data. The test results are as follows Figure 6 As shown, the results show that when the hollow second cathode sampling device is used for analysis, a signal intensity of 8.0×10-12 and good discharge stability can be obtained.

[0064] Embodiment 2:

[0065] The hollow second cathode sampling device and the SiC flakes were ultrasonically cleaned in a mixed solution of nitric acid (HNO3) and ultrapure water in a ratio of 1:1, and then ultrasonically cleaned twice in ultrapure water. Finally, they were washed with anhydrous ethanol and dried. The cleaned samples were loaded into the hollow second cathode sampling device, and after evacuation, the combination was loaded into the GD-MS sample cell for analysis. The optimized discharge voltage was 1.5 kV, the discharge current was 1.3 mA, and the discharge gas (Ar) flow rate was 1.0 cc / min. Then, the element signal intensity in the sample was measured over time to further characterize the stability of the method. At the same time, the same sample was subjected to a GD-MS signal intensity test using sputtering surfaces of different sizes of the hollow second cathode as the control group data. The test results are as follows. Figure 7 As shown, the results show that when the hollow second cathode W-shaped medium-sized sample injection device is used for analysis, a signal intensity of 1.0×10-11 and good discharge stability can be obtained.

[0066] Finally, it is necessary to explain here that the above embodiments are only used to further illustrate the technical solution of the present invention in detail and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present invention all fall within the scope of protection of the present invention.

Claims

1. A sample device for measuring non-conductor samples by a glow discharge mass spectrometer, comprising a second cathode sample introduction device, characterized in that: The second cathode sampling device includes a shell with an opening, a hollow metal sheet and a spring insert, wherein the hollow metal sheet has a hollow pattern and is fixed on the opening of the shell, the spring insert is fixed inside the shell and is in a compressed state, the sample is clamped between the hollow metal sheet and the spring insert, and the shell is provided with a groove at the opening for fixing the hollow metal sheet; the outer diameter of the shell is 35 mm, the thickness is 5.8 mm, and the inner diameter is 30.4 mm; the height of the spring insert is 4 mm; the outer diameter of the hollow metal sheet is 31.8 mm, the thickness is 0.25 mm, and the hollow shape is W style; the diameter of the groove is 32 mm; the hollow metal sheet participates in discharge as a hollow second cathode to produce sputtering, and the metal atoms produced by sputtering are redeposited on the sample surface to form a thin conductive layer.

2. The sample device for measuring non-conductor samples by glow discharge mass spectrometer according to claim 1, characterized in that: The hollow metal sheet is made of aluminum, copper, tantalum, gold, platinum or tungsten.

3. The sample device for measuring non-conductor samples by glow discharge mass spectrometer according to claim 1 or 2, characterized in that: The volume of the second cathode sample introduction device is smaller than the volume of the glow discharge cell so that it can be placed in the glow discharge cell.

4. A method for performing glow discharge mass spectrometer testing using the sample device according to any one of claims 1 to 3, characterized in that: The steps include: The sample to be tested and the hollow metal sheet are respectively cleaned with dilute acid, ultrapure water and anhydrous ethanol in advance, and dried; Loading the cleaned sample into the second cathode sample introduction device; The second cathode sample introduction device containing the sample is evacuated and then sent into the glow discharge cell of the glow discharge mass spectrometer; Connect the DC source and adjust the appropriate discharge pressure, discharge current and voltage for discharge; The elements to be measured in the sample are scanned and the signal intensity is recorded.

5. The method according to claim 4, characterized in that When cleaning the samples, the samples were first ultrasonically cleaned in dilute nitric acid, then ultrasonically cleaned twice in ultrapure water, and finally washed with anhydrous ethanol and dried.

6. The method according to claim 4 or 5, characterized in that: The display mode of the signal strength is current mode or voltage mode.

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