Method for accurately determining trace calcium in high-purity magnesium metal by combining membrane desolvation and triple quadrupole mass spectrometry

Abstract

The invention discloses a method for accurately measuring trace calcium in high-purity magnesium metal by combining membrane desolvation and triple quadrupole mass spectrometry, which comprises the following steps: (1) sequentially adding water to wet a high-purity magnesium sample and adding acid to dissolve the sample to obtain a digestion solution, and adding an internal standard solution into the digestion solution; (2) preparing calcium element solutions with multiple concentration gradients, adding the internal standard solution, fixing the volume, and shaking uniformly; (3) sequentially carrying out atomization treatment and membrane desolvation treatment on the prepared solution to respectively obtain dry aerosol of the to-be-detected solution and the standard solution; and (4) carrying out scanning determination on the dry aerosol of the solution to be detected and the standard solution in the step (3) by using a triple quadrupole mass spectrometer, and calculating to obtain the calcium content in the high-purity magnesium sample. According to the method, the 24Mg16O polyatomic interference brought by the matrix element and the mass spectrum interference of the working gas Ar on the to-be-detected element 40Ca are removed through membrane desolvation and triple quadrupole mass spectrometry, so that the trace calcium element in the high-purity magnesium sample can be accurately determined, and the lower determination limit can reach ppb level.

Description

Technical Field

[0001] The present invention relates to the technical field of material detection, and particularly to a method for accurately determining trace calcium in high-purity metallic magnesium by membrane desolvation-triple quadrupole mass spectrometry. Background Technique

[0002] With the development of applications in the field of materials and the continuous improvement of material quality, there is a requirement for the detection of trace calcium in high-purity magnesium, especially for pure magnesium samples with a purity higher than 99.99%. Currently, analysis using an inductively coupled plasma mass spectrometer is the mainstream trace analysis method, but there are serious mass spectrometry interferences and matrix effects during the actual measurement of calcium. There are multiple stable isotopes of calcium, including 40 Ca (96.94%), 42 Ca (0.65%), 43 Ca (0.14%), 44 Ca (2.09%), 48 Ca (0.19%). Selecting an isotope element with a higher abundance and lower mass spectrometry interference as the analysis element can improve the accuracy and precision of the determination.

[0003] When testing calcium by inductively coupled plasma mass spectrometry, 40 Ar seriously interferes with the detection of 40 Ca with a higher abundance and cannot be normally measured in the standard mode. Usually, a cold plasma mode, a collision mode, and a reaction mode are adopted. The cold plasma mode test is suitable for a sample environment without a matrix in a water environment or an acid environment. In high-purity magnesium samples, the first ionization energy of magnesium is 7.7 eV, and that of calcium is 6.1 eV. Under cold plasma conditions, the ion source can suppress part of the magnesium matrix, but the matrix effect at the interface becomes the main reason for inaccurate testing. In addition, due to 24 Mg 16 O and 40 Ca mass spectrometry interference, and it will be aggravated under cold plasma conditions 24 Mg 16 O polyatomic ion formation, bringing obvious matrix interference to the analysis and testing. The collision mode can significantly suppress 40 Ar mass spectrometry interference and 24 Mg 16 O polyatomic interference, but 40 Ca has a poor linear standard curve and low sensitivity. Therefore, the 44 Ca mass number with a lower abundance is often selected, but its sensitivity is also not high, resulting in an unsatisfactory test result for trace calcium elements. In the triple quadrupole mass spectrometer test, introducing reactive gases such as hydrogen, methane, and ammonia to react with argon can effectively reduce the interference of Ar on calcium ions. However, the effect of removing interference is not good. If a helium gas mixture is used, although the collision can reduce 24 Mg16 The interference caused by O polyatomic atoms, but at the same time, the signal of the element to be measured will also decrease due to collisions, resulting in a decrease in sensitivity, which is not conducive to the determination of low contents.

[0004] In summary, the core of the accurate analysis and detection of trace calcium in high-purity magnesium is to remove the interference brought by the matrix and the working gas argon, including the matrix effect caused by the matrix element magnesium and the formation of 24 Mg 16 O polyatomic interference and the mass spectrometry interference of the working gas 40 Ar on Ca ions. Therefore, there is an urgent need for a method that can accurately determine trace calcium in high-purity magnesium. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for accurately determining trace calcium in high-purity metallic magnesium by combining membrane desolvation and triple quadrupole mass spectrometry, so as to solve the problem that the existing method for detecting trace calcium in high-purity metallic magnesium cannot remove the interference brought by the matrix and the working gas, resulting in low determination accuracy.

[0006] To achieve the above purpose, the present invention provides a method for accurately determining trace calcium in high-purity metallic magnesium by combining membrane desolvation and triple quadrupole mass spectrometry, including the following steps:

[0007] (1) Accurately weigh a high-purity magnesium sample, then wet the high-purity magnesium sample with water and dissolve it with acid in sequence until a completely dissolved digestion solution is obtained. Add an internal standard solution to the digestion solution, and conduct a blank test along with the preparation of the digestion solution;

[0008] (2) Prepare calcium element solutions with multiple concentration gradients, add an internal standard solution, make up the volume to a constant volume, and shake well;

[0009] (3) Atomize and membrane desolvate the solutions prepared in step (1) and step (2) in sequence to obtain the dry aerosol of the solution to be detected and the dry aerosol of the standard solution respectively;

[0010] (4) Use a triple quadrupole mass spectrometer to scan and measure the dry aerosol of the solution to be detected and the dry aerosol of the standard solution in step (3) to obtain the intensity of the calcium element. Subsequently, use the concentration of the calcium element in the standard solution as the abscissa and the intensity of the corresponding measured calcium element as the ordinate to obtain a standard curve; then calculate the concentration of the calcium element in the solution to be detected from the standard curve, and finally calculate the calcium content in the high-purity magnesium sample.

[0011] For high-purity magnesium samples, first, on the one hand, the digestion solution after dissolving the magnesium sample is atomized to form an aerosol, and the generated wet aerosol is membrane desolvated. The solute and solvent are separated by heating gas purging, and the oxide yield will be greatly reduced, and the matrix tolerance of the instrument will be greatly improved; on the other hand, the removal of O, H, N and other ions in the solvent reduces the formation of the matrix element magnesium24 Mg 16 The mass spectrometry interference caused by O polyatomic atoms is eliminated to improve the accuracy of calcium element determination; then it enters a triple quadrupole mass spectrometer, and reaction gas is introduced into the collision reaction cell to remove the interference in the instrument. The argon ions of the atmospheric element undergo mass transfer or charge transfer to remove the mass spectrometry interference on the calcium element Ca to be measured. Through the removal of the two interferences, the accurate determination of trace calcium in high-purity magnesium is achieved.

[0012] Preferably, in step (1), the purity of the high-purity magnesium sample is above 99.99%.

[0013] Preferably, in step (1), the sample weighing amount of the high-purity magnesium sample is related to the purity of the high-purity magnesium sample. When the purity of the high-purity magnesium sample is higher than 99.999%, the sample weighing amount is not less than 0.25 g.

[0014] Preferably, in steps (1) and (2), the internal standard element in the internal standard solution is Sc, and the concentration of the internal standard solution is 20 ppb.

[0015] Preferably, in step (2), the atomization treatment is carried out in an atomizer. During the atomization treatment, the digestion solution forms a wet aerosol.

[0016] Preferably, in step (2), the membrane desolvation treatment is carried out in a membrane desolvation device. The temperature of the membrane desolvation device is 80 - 180 °C, and the gas flow rate is 0 - 10 L / min. After the wet aerosol passes through the membrane desolvation device, the O, H, and N elements in the solvent are effectively separated, and the wet aerosol is transformed into a dry aerosol. The dry aerosol at the outlet of the membrane desolvation device mainly exists as matrix magnesium ions and ions of the element to be measured.

[0017] Preferably, in step (3), the triple quadrupole mass spectrometer is equipped with a reaction gas. Select 40 Ca as the mass number to be analyzed, and adopt the tandem mode to test the intensity of the Ca element under mass in-situ scanning.

[0018] Preferably, in step (3), the injection system of the triple quadrupole mass spectrometer selects a hydrofluoric acid-resistant system, and the working conditions are: the ion source power is 1500 - 1600 W, the plasma flow rate is 12 - 17 L / min, the auxiliary gas flow rate is 0.5 - 1.0 L / min, the atomization carrier gas flow rate is 0.8 - 1.2 L / min, the reaction gas flow rate is 2 - 5 mL / min, and the hexapole offset is set to -6 - 10 V.

[0019] Preferably, in step (3), the reaction gas is a gas that can react with argon ions, and the reaction gas reacts with argon ions to undergo mass transfer to form polyatomic or neutral ions. Specifically, the reaction gas includes but is not limited to hydrogen, methane, ammonia, etc.

[0020] Preferably, in step (3), the calcium element content in the high-purity magnesium sample measured is at the ppb level.

[0021] Therefore, the method for accurately determining trace calcium in high-purity metallic magnesium by using the above-mentioned membrane desolvation-triple quadrupole mass spectrometry has the following beneficial effects:

[0022] (1) The present invention can make the wet aerosol when entering the plasma become a relatively dry aerosol through membrane desolvation treatment, so that the sample gas entering the triple quadrupole mass spectrometer hardly has a solvent part, greatly reducing the interference of oxides and hydroxides brought by the matrix magnesium to the element Ca to be measured; in addition, the significant decrease in the oxide content enhances the matrix interference resistance of the system, ensuring that the quality control standard of the sample test results can be met.

[0023] (2) The present invention uses a triple quadrupole mass spectrometer equipped with a collision reaction cell, introduces reactive gases such as hydrogen, methane, ammonia, etc. to carry out mass transfer or charge transfer processes with argon ions, removes the overlapping interference of the working gas argon at the mass number where the element calcium to be measured is located, and realizes accurate acquisition and accurate quantification of the calcium signal in situ.

[0024] (3) The present invention passes through membrane desolvation and triple quadrupole mass spectrometry twice to remove the polyatomic 24 Mg 16 O interference brought by the matrix element and the mass spectrometry interference of the working gas Ar to the element 40 Ca to be measured, and can realize the accurate determination of trace calcium elements in high-purity magnesium samples, and the lower limit of determination can reach the ppb level.

[0025] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0026] Figure 1 is the determination flow chart of the present invention;

[0027] Figure 2 is the standard curve graph;

[0028] In the figure: 1, nebulizer; 2, membrane desolvation device; 3, triple quadrupole mass spectrometer; 3-1, collision reaction cell. Specific Embodiments

[0029] The following will further describe the present invention. It should be noted that this embodiment is based on the present technical solution, and gives detailed implementation manners and specific operation processes, but the present invention is not limited to this embodiment.

[0030] Example 1

[0031] A method for accurately determining trace calcium in high-purity magnesium by membrane desolvation-triple quadrupole mass spectrometry, comprising the following steps:

[0032] (1) Accurately weigh 0.1000g of a high-purity magnesium sample with a purity of 99.99%. There are 6 parallel samples. Then place the high-purity magnesium sample in a polytetrafluoroethylene beaker, add water to moisten it and add acid to dissolve it in turn. The acid added is nitric acid. Heat it at a low temperature and the heating temperature is lower than 100°C until a completely dissolved digestion solution is obtained. Add the Sc internal standard solution to the digestion solution and adjust the volume to a 100mL volumetric flask. The final concentration of the Sc internal standard solution is 20ppb. Perform a blank test along with the preparation of the digestion solution.

[0033] (2) Prepare multiple calcium element solutions with concentration gradients, add Sc internal standard solution, adjust volume, and shake well. The final concentration of Sc internal standard solution is 20 ppb, and the concentrations of calcium element solutions are 0.5 ppb, 1.0 ppb, 5 ppb, 10 ppb, and 20 ppb, respectively.

[0034] (3) subjecting the solutions prepared in step (1) and step (2) to atomization treatment and membrane desolvation treatment in sequence to obtain a dry aerosol of the solution to be tested and a dry aerosol of the standard solution, respectively;

[0035] The atomization process is performed in the atomizer 1, and during the atomization process, the digestion solution forms a wet aerosol;

[0036] The membrane desolventizing treatment is carried out in the membrane desolventizing device 2. The temperature of the membrane desolventizing device 2 is 120°C and the gas flow rate is 2L / min. After the wet aerosol passes through the membrane desolventizing device 2, the elements O, H, N and others in the solvent are effectively separated and the wet aerosol is transformed into a dry aerosol. A large number of element oxides, hydroxides and tiny hydrate molecules are removed. The dry aerosol at the outlet of the membrane desolventizing device 2 mainly exists in the form of matrix magnesium ions and ions of the element to be measured. At this time, the system 24 Mg 16 The interference from O polyatomic formation is reduced.

[0037] (4) Scanning and measuring the dry aerosol of the test solution and the dry aerosol of the standard solution in step (3) using a triple quadrupole mass spectrometer 3 to obtain the intensity of the calcium element; specifically, the instrument uses a TQMS1000 triple quadrupole mass spectrometer produced by Gangyan Nano, and the triple quadrupole mass spectrometer 3 is configured with a reaction gas of hydrogen. 40 Ca was used as the mass number to be analyzed, and the intensity of the Ca element was tested under mass in-situ scanning in tandem mode;

[0038] A collision reaction cell 3-1 is provided in the triple quadrupole mass spectrometer 3. The injection system of the triple quadrupole mass spectrometer 3 uses a hydrofluoric acid-resistant system. The working conditions are as follows: the ion source power is 1550 W, the plasma flow rate is 15 L / min, the auxiliary gas flow rate is 0.85 L / min, the nebulizing carrier gas flow rate is 0.99 L / min, the hydrogen gas flow rate is 3.5 mL / min, and the hexapole offset is set to -8 V;

[0039] Subsequently, taking the concentration of calcium element in the standard solution as the abscissa and the measured intensity of calcium element as the ordinate, a standard curve is obtained; then the concentration of calcium element in the solution to be detected is calculated from the standard curve, and finally the calcium content in the high-purity magnesium sample is calculated.

[0040] The standard curve is shown in Figure 2 , and the specific test results are as follows:

[0041] Table 1 Test results of the standard curve

[0042]

[0043] The high-purity magnesium sample is determined in parallel 6 times. The test results are shown in Table 2. The average value of the calcium content obtained is 0.605 μg / g, and the relative error is less than 5%. 5 ppb of the element calcium to be detected is added to the solution to be detected. The test results are shown in Table 2, and the spike recovery rate is between 100% and 120%. It shows that the method of the present invention can accurately determine the trace calcium in high-purity magnesium metal.

[0044] Table 2 Test results of trace calcium in high-purity magnesium

[0045]

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for accurately determining trace calcium in high-purity magnesium metal by membrane desolvation-triple quadrupole mass spectrometry, characterized in that: The following steps are involved: (1) Accurately weigh the high-purity magnesium sample, then add water to wet the high-purity magnesium sample and add acid to dissolve it in turn until a completely dissolved digestion solution is obtained, add the internal standard solution to the digestion solution, and perform a blank test along with the preparation of the digestion solution; (2) Prepare calcium solutions with multiple concentration gradients, add internal standard solution, make up to volume, and shake well; (3) subjecting the solutions prepared in step (1) and step (2) to atomization treatment and membrane desolvation treatment in sequence to obtain a dry aerosol of the solution to be tested and a dry aerosol of the standard solution, respectively; (4) Using a triple quadrupole mass spectrometer to scan and measure the dry aerosol of the test solution and the dry aerosol of the standard solution in step (3), the intensity of the calcium element is obtained, and then the concentration of the calcium element in the standard solution is used as the horizontal coordinate and the corresponding measured calcium element intensity is used as the vertical coordinate to obtain a standard curve; then the concentration of the calcium element in the test solution is calculated from the standard curve, and finally the calcium content in the high-purity magnesium sample is calculated.

2. The method for accurately determining trace calcium in high-purity metallic magnesium by membrane desolvation-triple quadrupole mass spectrometry according to claim 1, wherein: In step (1), the purity of the high-purity magnesium sample is above 99.99%.

3. The method for accurately determining trace calcium in high-purity magnesium by membrane desolvation-triple quadrupole mass spectrometry according to claim 1, characterized in that: In step (1), the weight of the high-purity magnesium sample is related to the purity of the high-purity magnesium sample. When the purity of the high-purity magnesium sample is higher than 99.999%, the weight of the sample is not less than 0.25 g.

4. A method for accurately determining trace calcium in high-purity magnesium metal by membrane desolvation-triple quadrupole mass spectrometry according to claim 1, characterized in that: In step (1) and step (2), the internal standard element in the internal standard solution is Sc, and the concentration of the internal standard solution is 20 ppb.

5. A method for accurately determining trace calcium in high-purity magnesium metal by membrane desolvation-triple quadrupole mass spectrometry in combination, as claimed in claim 1, wherein: In step (2), the atomization treatment is carried out in an atomizer, and during the atomization treatment process, the digestion solution forms a wet aerosol.

6. A method for accurately determining trace calcium in high-purity metallic magnesium by membrane desolvation-triple quadrupole mass spectrometry in combination, according to claim 5, characterized in that: In step (2), the membrane desolventizing treatment is carried out in a membrane desolventizing device, the temperature of the membrane desolventizing device is 80-180°C, the gas flow rate is 0-10L / min, and after the wet aerosol passes through the membrane desolventizing device, the O, H, and N elements in the solvent are effectively separated and the wet aerosol is converted into a dry aerosol. The dry aerosol at the outlet of the membrane desolventizing device mainly exists in the form of matrix magnesium ions and ions of the element to be measured.

7. A method for accurately determining trace calcium in high-purity magnesium metal by membrane desolvation-triple quadrupole mass spectrometry according to claim 1, characterized in that: In step (3), the triple quadrupole mass spectrometer is configured with a reaction gas, and 40 Ca is selected as the mass number to be analyzed. In the tandem mode, the intensity of the Ca element is measured under mass in-situ scanning.

8. A method for accurately determining trace calcium in high-purity magnesium by membrane desolvation-triple quadrupole mass spectrometry according to claim 1, characterized in that: In step (3), the injection system of the triple quadrupole mass spectrometer uses a hydrofluoric acid resistant system, and the operating conditions are: ion source power is 1500~1600W, plasma flow rate is 12~17L / min, auxiliary gas flow rate is 0.5~1.0L / min, nebulizer carrier gas flow rate is 0.8~1.2L / min, reaction gas flow rate is 2~5mL / min, and the hexapole bias is set to -6~-10V.

9. A method for accurately determining trace calcium in high-purity metallic magnesium by membrane desolvation-triple quadrupole mass spectrometry according to claim 8, characterized in that: The reaction gas is a gas that can react with argon ions, and mass transfer occurs between the reaction gas and the argon ions to form polyatomic or neutral ions.

10. A method for accurately determining trace calcium in high-purity magnesium metal by membrane desolvation-triple quadrupole mass spectrometry according to claim 1, characterized in that: In step (3), the calcium content of the high-purity magnesium sample measured is at the ppb level.

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