GB/T 12690.13-2026Chemical analysis methods for non-rare earth impurities in rare earth metals and their oxides - Part 13: Determination of molybdenum and tungsten content (English PDF)

4.2.5 Ammonia (1 3). GB/T 12690.13-2025

4.2.6 Boric acid solution (50g/L). Weigh 5g of boric acid and dissolve it in 100mL of water.

4.2.7 Molybdenum Standard Stock Solution. Weigh 0.1500 g of molybdenum oxide that has been dried at 110°C for 1 h and cooled to room temperature in a desiccator [w] [(MoO3)>=99.99%], placed in a 50mL plastic beaker, added 20mL of ammonia water (4.2.5) until completely dissolved. If molybdenum oxide is not completely dissolved... Solution. Add 5 mL of ammonia water (4.2.5) and heat in a 50°C water bath for 5 minutes. Cool and then make up to volume; transfer to a 100 mL plastic volumetric flask. Dilute with water to the mark and mix well. 1 mL of this solution contains 1 mg of molybdenum.

4.2.8 Tungsten Standard Stock Solution. Weigh 0.1261 g of tungsten trioxide that has been dried at 110°C for 1 h and cooled to room temperature in a desiccator [w] [(WO3)>=99.99%], placed in a 50mL plastic beaker, added 20mL water and 2.0g sodium hydroxide (4.2.1) and dissolved completely. If trioxide If the tungsten hydroxide is not completely dissolved, add 1.0g of sodium hydroxide (4.2.1) and stir until dissolved. Avoid adding too much (excess will cause problems during subsequent acidification). (Precipitation); transfer to a 100mL plastic volumetric flask, dilute to the mark with water, and mix well. 1mL of this solution contains 1mg of tungsten.

4.2.9 Molybdenum and Tungsten Mixed Standard Solution. Transfer

5.00 mL of molybdenum standard stock solution (4.2.7) and tungsten standard stock solution (4.2.8) to... Add 5 mL of hydrofluoric acid (4.2.3) to a 100 mL plastic volumetric flask, dilute to the mark with water, and mix well. 1 mL of this solution contains 50 µg of molybdenum and... 50 µg tungsten.

4.2.10 Argon. Volume fraction not less than 99.99%.

4.3 Instruments and Equipment Inductively coupled plasma atomic emission spectrometers (ICP-AES) can be used if they meet the following specifications under optimal operating conditions.

---Complies with the verification procedures and technical specifications in JJG768.

---The recommended analytical spectral wavelengths for element determination are shown in Table 1.

4.4 Samples

4.4.1 Weigh the rare earth metal shavings sample immediately after it is taken out.

4.4.2 Clean the surface of the rare earth metal block. Use a 6mm diameter drill bit to drill 3 points at equal intervals on both the top and bottom surfaces of the metal ingot, then discard the drill bit. Remove drill chips 0.5mm~1.0mm from the surface of the ingot, then drill a sample with a 4mm diameter drill bit, taking a sample of no less than 10g. The sample should be quickly mixed and reduced to 4 portions, and weighed immediately according to the required sample amount.

4.5 Test Procedure

4.5.1 Sample Weigh 1.00g of sample (4.4), accurate to 0.0001g.

4.5.2 Parallel Tests Perform two parallel experiments.

4.5.3 Blank Test A blank test was performed along with the sample. GB/T 12690.13-2025

4.5.4 Preparation of analytical solutions

4.5.4.1 Place the sample (4.5.1) in a.200 mL PTFE beaker and moisten it with a small amount of water. Add 10 mL of nitric acid (4.2.4), low... Dissolve by gentle heating until clear. Add 50 mL of water and 5 mL of hydrofluoric acid (4.2.3), heat to near boiling, and maintain the temperature on an 80°C hot plate. 10 min. Allow to cool to room temperature, transfer to a 100 mL plastic volumetric flask, dilute to the mark with water, and mix well. After the precipitate settles, use a double-layer chromatography system. Slow-speed dry filtration with filter paper.

4.5.4.2 Transfer

10.00 mL of the test solution (4.5.4.1) into a 50 mL plastic volumetric flask, add 5 mL of boric acid solution (4.2.6) and 1 mL of nitric acid. (4.2.2) Dilute with water to the mark, mix well, and then test.

Note. If the instrument is equipped with a hydrofluoric acid resistant injection system, boric acid solution can be omitted (4.2.6).

4.5.5 Preparation of Standard Solutions Transfer 0 mL,

0.10 mL,

0.50 mL,

10.00 mL of a mixed molybdenum and tungsten standard solution, respectively. (4.2.9) Add 4 drops (approximately

0.2 mL) of hydrofluoric acid (4.2.3) and 5 mL of boric acid solution (4.2.6) to seven 50 mL plastic volumetric flasks. 1 mL of nitric acid (4.2.2) was diluted to the mark with water and mixed well. The molybdenum and tungsten concentrations of this series of standard solutions were 0 µg/mL and 0 µg/mL, respectively. 0.10µg/mL, 0.50µg/mL, 1.00µg/mL, 2.50µg/mL, 5.00µg/mL, 10.00µg/mL.

Note. If the instrument is equipped with a hydrofluoric acid resistant injection system, boric acid solution can be omitted (4.2.6).

4.5.6 Measurement

4.5.6.1 Drawing the working curve Under the selected instrument operating conditions, the series of standard solutions (4.5.5) were subjected to argon plasma spectroscopy using the selected analytical lines. Plot a working curve with the light signal intensity of the analyte as the ordinate and the mass concentration of a series of standard solutions as the abscissa. The linear correlation coefficient should not exceed [value missing]. Less than 0.9995.

4.5.6.2 Determination of blank test solution After the working curve (4.5.6.1) meets the requirements for determination, the blank test (4.5.3) solution is subjected to argon plasma analysis using the selected analytical lines. Bulk spectroscopy determination. The instrument automatically processes data based on the working curve, calculates and outputs the mass concentration of the analyte in the blank test solution.

4.5.6.3 Determination of analytical solutions After the working curve (4.5.6.1) meets the requirements for determination, the analytical solution (4.5.4.2) is subjected to argon plasma analysis using the selected analytical line. Spectroscopic determination. The instrument automatically processes data based on the working curve, calculates and outputs the mass concentration of the analyte in the analytical solution.

4.6 Experimental Data Processing The content of molybdenum or tungsten is expressed as a mass fraction w(i) and calculated according to formula (1).

4.7 Precision

4.7.1 Repeatability Under repeatability conditions, the absolute difference between two independent test results does not exceed the repeatability limit (r); otherwise, the result is considered acceptable. The repeatability limit (r) is determined by linear interpolation or extrapolation based on the data in Table 2, provided that the limit is no more than 5%.

4.7.2 Reproducibility Under reproducibility conditions, the absolute difference between two independent test results should not exceed the reproducibility limit (R). For cases where the reproducibility limit (R) is less than 5%, the reproducibility limit (R) is obtained using linear interpolation or extrapolation based on the data in Table 3.

5.2.9 Molybdenum and Tungsten Mixed Standard Solution. Transfer

1.00 mL of molybdenum standard stock solution (5.2.7) and tungsten standard stock solution (5.2.8) to... Add 5 mL of hydrofluoric acid (5.2.3) to a.200 mL plastic volumetric flask, dilute to the mark with water, and mix well. 1 mL of this solution contains 500 ng of molybdenum and... 500ng tungsten.

5.2.10 Cesium internal standard stock solution. Weigh 0.1270 g of cesium chloride, add 10 mL of water and 2 mL of nitric acid (5.2.2), dissolve until clear, and cool. Transfer to a 100 mL volumetric flask, dilute to the mark with water, and mix well. 1 mL of this solution contains 1 mg of cesium.

5.2.11 Thallium internal standard stock solution. Weigh 0.1173 g thallium chloride, add 10 mL water, dissolve completely, add 10 mL nitric acid (5.2.2), and transfer to... Dilute to the mark with water in a 100mL volumetric flask and mix well. 1mL of this solution contains 1mg of thallium.

5.2.12 Rhodium internal standard stock solution. Weigh

0.256 g of rhodium chloride hydrate, add 10 mL of water, dissolve completely, and add 10 mL of nitric acid. (5.2.2) Transfer to a 100 mL volumetric flask, dilute to the mark with water, and mix well. 1 mL of this solution contains 1 mg of rhodium.

5.2.13 Cesium, Rhodium, and Thallium Internal Standard Mixed Solution. Transfer

1.00 mL of cesium internal standard stock solution (5.2.10) and

1.00 mL of thallium internal standard stock solution. (5.2.11) and

1.00 mL of rhodium internal standard stock solution (5.2.12) were placed in a 1000 mL volumetric flask, 2 mL of nitric acid (5.2.2) was added, and the solution was diluted with water. Fill to the mark and mix well. 1 mL of this solution contains 1 µg of cesium, rhodium, and thallium.

5.2.14 Argon. Volume fraction not less than 99.99%.

5.3 Instruments and Equipment Inductively coupled plasma mass spectrometry (ICP-MS) instruments that meet the following specifications under optimal operating conditions can be used.

---The calibration items and technical specifications of the quadrupole plasma mass spectrometer meet the requirements of JJF1159.

---The isotopic mass numbers of the elements are shown in Table 4.

5.4 Samples

5.4.1 Weigh the rare earth metal sample immediately after it is taken out.

5.4.2 For bulk rare earth metals, grind the surface clean, and use a 6mm diameter drill bit to drill 3 points at equal intervals on both the top and bottom surfaces of the metal ingot, discarding the samples. Remove drill chips 0.5mm~1.0mm from the surface of the ingot, then drill a sample with a 4mm diameter drill bit, taking a sample of no less than 10g. The sample should be quickly mixed and reduced to 4 portions, and weighed immediately according to the required sample amount.

5.5 Test Procedure

5.5.1 Sample Weigh 1.00g of sample (5.4), accurate to 0.0001g.

5.5.2 Parallel Tests Perform two parallel experiments.

5.5.3 Blank Test A blank test was performed along with the sample.

5.5.4 Preparation of analytical solutions

5.5.4.1 Place the sample (5.5.1) in a.200 mL PTFE beaker and moisten it with a small amount of water. Add 10 mL of nitric acid (5.2.4), low... Dissolve by gentle heating until clear. Add 50 mL of water and 5 mL of hydrofluoric acid (5.2.3), heat to near boiling, and maintain the temperature on an 80°C hot plate. 10 min. Allow to cool to room temperature, transfer to a 100 mL plastic volumetric flask, dilute to the mark with water, and mix well. After the precipitate settles, use a double-layer chromatography system. Slow-speed dry filtration with filter paper.

5.5.4.2 Transfer the corresponding volume of test solution (5.5.4.1) according to Table 5 into a.200mL plastic volumetric flask, and add 5mL of boric acid solution (5.2.6). 4 mL of nitric acid (5.2.2) and 2 mL of a mixed solution of cesium, rhodium, and thallium internal standards (5.2.13) are diluted with water to the mark, mixed well, and ready for testing.

Note. If the instrument is equipped with a hydrofluoric acid-resistant injection system, boric acid solution is not required (5.2.6); when using an instrument with an online internal standard solution addition device, no boric acid solution is needed. The mixed internal standard solution of cesium, rhodium, and thallium (5.2.13) is used. The concentration of the mixed internal standard solution of cesium, rhodium, and thallium in the online determination solution is controlled according to the addition ratio of the device. The concentration was 10 ng/mL.

5.5.5 Preparation of Standard Solutions Transfer 0 mL,

0.10 mL,

0.20 mL,

10.00 mL of a mixed molybdenum and tungsten standard solution, respectively. (5.2.9) Add 4 drops (approximately

0.2 mL) of hydrofluoric acid (5.2.3) and 5 mL of boric acid solution (5.2.6) to seven 100 mL plastic volumetric flasks. 2 mL of nitric acid (5.2.2) and 1 mL of a mixed solution of cesium, rhodium, and thallium internal standards (5.2.13) are diluted to the mark with water and mixed well. This series of standard solutions... The concentrations of molybdenum and tungsten were 0 ng/mL,

0.50 ng/mL,

10.00 ng/mL, and

25.00 ng/mL, respectively.

Note. If the instrument is equipped with a hydrofluoric acid-resistant injection system, boric acid solution is not required (5.2.6); when using an instrument with an online internal standard solution addition device, no boric acid solution is needed. The mixed internal standard solution of cesium, rhodium, and thallium (5.2.13) is used. The concentration of the mixed internal standard solution of cesium, rhodium, and thallium in the online determination solution is controlled according to the addition ratio of the device. The concentration was 10 ng/mL.

5.5.6 Measurement

5.5.6.1 Drawing the working curve After the inductively coupled plasma mass spectrometer has stabilized, under the selected instrument operating conditions, the mass numbers of the analyte and internal standard elements are measured. The ion current signal intensity of the analyte and internal standard element in a series of standard solutions (5.5.5) was measured sequentially. The analyte in the series of standard solutions was then used as the reference. The mass concentration of each element is plotted on the x-axis, and the ratio of the ion current signal intensity of the analyte to that of the internal standard is plotted on the y-axis to create a working curve. The linear correlation coefficient of the element should not be less than 0.9995; otherwise, it is necessary to re-standardize or prepare a new series of standard solutions for standardization.

5.5.6.2 Determination of blank test solution After the working curve (5.5.6.1) meets the requirements for determination, the blank test (5.5.3) solution is subjected to argon plasma chromatography with the selected analytical mass number. Daughter mass spectrometry determination. The instrument automatically processes data based on the working curve, calculates and outputs the mass concentration of the analyte in the blank test solution.

5.5.6.3 Determination of analytical solutions After the working curve (5.5.6.1) meets the requirements for determination, the analytical solution (5.5.4.2) is subjected to argon plasma treatment with the selected analytical mass number. Mass spectrometry. The instrument automatically processes data based on the working curve, calculates and outputs the mass concentration of the analyte in the analytical solution.

5.6 Experimental Data Processing The content of molybdenum or tungsten is expressed as a mass fraction w(j) and calculated according to formula (2).

5.7 Precision

5.7.1 Repeatability Under repeatability conditions, the absolute difference between two independent test results does not exceed the repeatability limit (r); otherwise, the result is considered acceptable. The repeatability limit (r) is determined by linear interpolation or extrapolation based on the data in Table 6, provided that the limit is no more than 5%.

5.7.2 Reproducibility Under reproducibility conditions, the absolute difference between two independent test results should not exceed the reproducibility limit (R). If the absolute difference exceeds the reproducibility limit (R), then... The reproducibility limit (R) is determined by linear interpolation or extrapolation based on the data in Table 7, provided that the reproducibility limit does not exceed 5%. GB/T 12690.13-2026. Chemical analysis methods for non-rare earth impurities in rare earth metals and their oxides - Part 13. Determination of molybdenum and tungsten content ICS

14 National Standards of the People's Republic of China ...