GB/T 13748.3-2026Methods for chemical analysis of magnesium and magnesium alloys - Part 3: Determination of lithium and silver content - Flame atomic absorption spectrometry (English PDF)

6.2.3 Nitric acid (1 1). Transfer 500 mL of nitric acid (rho=

1.42 g/mL, analytical grade) to 500 mL of water and mix well.

6.2.4 Sulfuric acid (1 1). Transfer 500 mL of sulfuric acid (rho=

1.84 g/mL, analytical grade) to 500 mL of water and mix well.

6.2.5 Lithium Standard Stock Solution (1 mg/mL). Weigh 5.3228 g of lithium carbonate (wLi2CO3>=99.99%) into a 500 mL beaker, and slowly... Add 120 mL of nitric acid (1.9), heat until completely dissolved, boil for 5 minutes, and cool to room temperature. Transfer the solution to a 1000 mL volumetric flask. Dilute with water to the mark and mix well. 1 mL of this solution contains 1 mg of lithium. Alternatively, prepare using a certified standard solution.

6.2.6 Lithium Standard Solution A (10 µg/mL). Transfer

10.00 mL of lithium standard stock solution (6.2.5) to a 1000 mL volumetric flask, and add water. Dilute to the mark and mix well. 1 mL of this solution contains 10 µg of lithium.

6.2.7 Lithium Standard Solution B (50 µg/mL). Transfer

5.00 mL of lithium standard stock solution (6.2.5) to a 100 mL volumetric flask and dilute with water. Dilute to the mark and mix well. 1 mL of this solution contains 50 µg of lithium.

6.2.8 Magnesium Solution A (20 mg/mL). Weigh

20.00 g of magnesium (wMg >= 99.99%, wLi <= 0.0005%) into a.2000 mL beaker. Add 600 mL of nitric acid in portions (6.2.3), cover with a watch glass, heat until completely dissolved, cool to room temperature, and transfer to a 1000 mL container. Dilute with water to the mark in a volumetric flask and mix well.

6.2.9 Magnesium Solution B (1 mg/mL). Transfer

25.0 mL of magnesium solution A (6.2.8) to a 500 mL volumetric flask and dilute to the mark with water. Mix well.

6.3 Test Procedure

6.3.1 Sample Weigh 0.50g of the sample (Chapter 5), accurate to 0.0001g, and record it as m0.

6.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

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

6.3.4 Measurement

6.3.4.1 Place the sample in a 250mL beaker, add 10mL of water, and slowly add 10mL of nitric acid (6.2.3). Wait until the vigorous reaction stops. Then add 10 mL of nitric acid (6.2.3), and a few drops of hydrogen peroxide (6.2.1) can be added to dissolve it. Cover with a watch glass and heat until completely dissolved. If any... Dissolve the solids, filter and wash. Place the residue and filter paper in a platinum crucible, ashed, ignite at 550°C, and cool. Add 2 mL of sulfuric acid (6.2.4). Add 5 mL of hydrofluoric acid (6.2.2) and nitric acid (6.2.3) dropwise until the solution is clear. Heat to evaporate to near dryness, ignite at 750°C for 5 minutes, and then cool. Bring to room temperature, dissolve the residue with a small amount of nitric acid (6.2.3), filter if necessary, and combine the filtrate with the original test solution.

6.3.4.2 Transfer the test solution (including the combined solution after treating insoluble matter) into the corresponding volumetric flask according to Table 1, dilute with water to the mark, and mix well.

6.3.4.3 At a wavelength of 670.8 nm using a flame atomic absorption spectrometer, an air-acetylene lean flame was used, with water used for zeroing, and compared with the corresponding series of standard... Simultaneously measure the absorbance of lithium in the standard solution, and find the corresponding lithium mass concentration (rhoLi) from the working curve.

6.3.5 Plotting the Working Curve

6.3.5.1 Based on the mass fraction of lithium in the sample, a series of standard solutions shall be prepared in the following manner.

---When the lithium mass fraction is 0.0020%~0.010%. transfer 0 mL,

5.00 mL of lithium standard solution A (6.2.6) was placed into six 100 mL volumetric flasks, and 25 mL of magnesium solution A was added to each flask. (6.2.8) and 5 mL of nitric acid (6.2.3), dilute with water to the mark, and mix well.

---When the lithium mass fraction is greater than 0.010%~0.050%. transfer 0 mL,

5.00 mL of lithium standard solution B (6.2.7) was placed into six 100 mL volumetric flasks, and 25 mL of magnesium solution A was added to each flask. (6.2.8) and 5 mL of nitric acid (6.2.3), dilute with water to the mark, and mix well.

---When the lithium mass fraction is greater than 0.050%~0.250%. transfer 0 mL,

5.00 mL of lithium standard solution A (6.2.6) was placed into six 100 mL volumetric flasks, and 1 mL of magnesium solution A was added to each flask. (6.2.8) Dilute with water to the mark and mix well.

---Lithium mass fraction greater than 0.250%~2.50%. Transfer 0 mL,

0.50 mL,

5.00 mL of lithium standard solution A (6.2.6) were placed in seven 100 mL volumetric flasks, and 2 mL of magnesium solution was added to each flask. Liquid B (6.2.9) is diluted with water to the mark and mixed well.

---Lithium mass fraction greater than 2.50%~16.00%. Transfer 0 mL,

0.50 mL,

4.00 mL of lithium standard solution B (6.2.7) was placed into six 100 mL volumetric flasks, and 1 mL of magnesium solution B was added to each flask. (6.2.9) Dilute with water to the mark and mix well.

6.3.5.2 The series of standard solutions were subjected to flame atomic absorption spectrometry at a wavelength of 670.8 nm using an air-acetylene lean flame, and adjusted with water. Zero, measure the absorbance of a series of standard solutions. Plot a working curve with the lithium mass concentration on the x-axis and the corresponding absorbance on the y-axis.

6.5 Precision

6.5.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 2, represent the two test results. The absolute difference should not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) should not exceed 5%. The repeatability limit (r) is calculated using linear data from Table 2. It can be obtained by interpolation or extension.

6.5.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 3, represent the two test results. The absolute difference should not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) should not exceed 5%. The reproducibility limit (R) is determined according to the data in Table 3. Obtained by linear interpolation or extrapolation.

7.2.1 Nitric acid (1 1). Transfer 500 mL of nitric acid (rho=

1.42 g/mL, analytical grade) and dissolve it in 500 mL of water, then mix well.

7.2.2 Thiourea solution (50 g/L).

7.2.3 Silver standard stock solution (1 mg/mL). Prepared as follows, or using a certified standard solution.

---Weigh 0.2500g of silver (wAg>=99.99%) into a 500mL beaker, add 20mL of nitric acid (7.2.1), and cover with a top coat. Heat the solution in a dish until completely dissolved, then continue heating to boiling to remove nitrogen oxides. Cool, transfer to a 250 mL volumetric flask, and dilute with water. Dilute to the mark and mix well. 1 mL of this solution contains 1 mg of silver.

---Weigh 1.5748g of silver nitrate (standard) and dissolve it in 100mL of water. Transfer the solution to a 1000mL volumetric flask and dilute to the mark with water. Uniform. 1 mL of this solution contains 1 mg of silver.

7.2.4 Silver Standard Solution (50 µg/mL). Transfer

25.00 mL of the silver standard stock solution (7.2.3) to a 500 mL volumetric flask and dilute with water. Fill to the mark and mix well. 1 mL of this solution contains 50 µg of silver.

7.2.5 Magnesium Solution A (20 mg/mL). Weigh

20.00 g of magnesium (wMg >= 99.99%, wAg <= 0.0005%) into a.2000 mL beaker. Add 600 mL of nitric acid (7.2.1) in portions, cover with a watch glass, heat until completely dissolved, cool to room temperature, and transfer to a 1000 mL container. Dilute with water to the mark in a volumetric flask and mix well.

7.2.6 Magnesium Solution B (1 mg/mL). Transfer

25.0 mL of magnesium solution A (7.2.5) to a 500 mL volumetric flask and dilute to the mark with water. Mix well.

7.3 Test Procedure

7.3.1 Sample Weigh 0.50g of the sample (Chapter 5), accurate to 0.0001g, and record it as m1.

7.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

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

7.3.4 Measurement

7.3.4.1 Place the sample in a 250mL beaker, add 10mL of water, slowly add 10mL of nitric acid (7.2.1), cover with a watch glass, and wait for the reaction to proceed. After the strong reaction has stopped, add 10 mL of nitric acid (7.2.1), heat until the sample is completely dissolved, rinse the beaker with water, boil, and then remove and cool. Room temperature.

7.3.4.2 Operate according to the different silver contents in the sample.

---When the silver mass fraction is 0.010%~0.100%, transfer the test solution into a 100mL (V3) volumetric flask and add 2mL of nitric acid. (7.2.1) 2 mL of thiourea solution (7.2.2), dilute with water to the mark and mix well.

---When the silver mass fraction is greater than 0.100%~1.00%, transfer the test solution to a 100mL (V3) volumetric flask and dilute with water to the mark. Mix thoroughly. Then transfer

10.00 mL of the test solution (V4) to a 100 mL (V5) volumetric flask, add 2 mL of nitric acid (7.2.1), 2 mL of... Thiourea solution (7.2.2), dilute with water to the mark and mix well.

---When the silver mass fraction is greater than 1.00%~4.00%, transfer the test solution to a 500mL (V3) volumetric flask, dilute with water to the mark, and mix. Mix well. Then transfer

10.00 mL of the test solution (V4) to a 100 mL (V5) volumetric flask, add 2 mL of nitric acid (7.2.1) and 2 mL of thiourea. Dilute the solution (7.2.2) with water to the mark and mix well.

7.3.4.3 Using an air-acetylene lean flame, at a wavelength of 328.1 nm on the atomic absorption spectrometer, zeroed with water, and compared with the corresponding series of standards. Simultaneously measure the absorbance of silver in the standard solution, and find the corresponding silver mass concentration (rhoAg) from the working curve.

7.3.5 Plotting the Working Curve

7.3.5.1 Prepare a series of silver standard solutions with different contents according to the following method.

---When the silver mass fraction is 0.010%~0.100%. transfer 0 mL,

10.00 mL of silver standard solution (7.2.4) were placed in seven 100 mL volumetric flasks, and 25 mL of magnesium solution was added to each flask. A (7.2.5), 5 mL nitric acid (7.2.1), 2 mL thiourea solution (7.2.2), dilute with water to the mark, and mix well.

---When the silver mass fraction is greater than 0.100%~1.00%. transfer 0 mL,

10.00 mL of silver standard solution (7.2.4) were placed in seven 100 mL volumetric flasks, and

2.5 mL of magnesium solution was added to each flask. A (7.2.5), 2 mL nitric acid (7.2.1), 2 mL thiourea solution (7.2.2), dilute with water to the mark, and mix well.

---When the silver mass fraction is greater than 1.00%~4.00%. transfer 0 mL,

8.00 mL. Silver standard solution (7.2.4) was placed in six 100 mL volumetric flasks, and 10 mL of magnesium solution B (7.2.6) and 2 mL of nitric acid were added. (7.2.1) 2 mL of thiourea solution (7.2.2), dilute with water to the mark and mix well.

7.3.5.2 The series of standard solutions were analyzed using an air-acetylene lean flame at a wavelength of 328.1 nm on a flame atomic absorption spectrometer, with water added. Zero, measure the absorbance of a series of standard solutions. Plot a working curve with the mass concentration of silver on the x-axis and the corresponding absorbance on the y-axis.

7.5 Precision

7.5.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 4, represent the two test results. The absolute difference does not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is defined using linear data from Table 4. It can be obtained by interpolation or extension.

7.5.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 5, represent the two test results. The absolute difference does not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) does not exceed 5%. The reproducibility limit (R) is calculated using linear regression based on the data in Table 5. It can be obtained by interpolation or extension.