GB/T 20975.17-2020Methods for chemical analysis of aluminium and aluminium alloys—Part 17: Determination of strontium content (English PDF)

4.1 Method summary

Dissolve the sample with hydrochloric acid and hydrogen peroxide, measure the absorbance of strontium using air-acetylene rich flame at the wavelength of 460.7 nm of a flame atomic absorption spectrometer, to determine the strontium content.

4.2 Reagents

Unless otherwise stated, only reagents and laboratory grade 2 water confirmed to be of analytical grade are used in the analysis.

4.2.1 Pure aluminum (wAl >= 99.99 %, wSr <= 0.001 %).

4.2.2 Hydrogen peroxide (rho = 1.10 g/mL).

4.2.3 Hydrofluoric acid (rho = 1.14 g/mL).

4.2.4 Nitric acid (rho = 1.42 g/mL).

4.2.5 Hydrochloric acid (1 + 1).

4.2.6 Lanthanum chloride solution (200 g/L): WEIGH 100 g of lanthanum chloride (LaCl3 · 6H2O), DILUTE to a 500 mL volumetric flask with water.

4.2.7 Aluminum solution A (20 mg/mL): WEIGH 20.00 g of pickled pure aluminum (4.2.1) and PLACE it in a 1000 mL beaker, COVER it with a watch glass, and ADD a total of 200 mL of hydrochloric acid (4.2.5) in portions. After the violent reaction stops, ADD a few drops of hydrogen peroxide (4.2.2), HEAT slowly until completely dissolved, and COOL down. TRANSFER the solution into a 1000 mL volumetric flask, DILUTE to the mark with water, and MIX well.

4.2.8 Aluminum solution B (2 mg/mL): PIPETTE 50 mL of aluminum solution (4.2.7) into a 500 mL volumetric flask, DILUTE to the mark with water, and MIX well.

4.2.9 Strontium standard storage solution: WEIGH 1.6850 g of strontium carbonate (wSrCO3 >= 99.99 %) and DISSOLVE it in an appropriate amount of hydrochloric acid (4.2.5), HEAT to boil, COOL down, DILUTE to 1000 mL with water, and MIX well. 1 mL of this solution contains 1.0 mg of strontium.

4.2.10 Strontium standard solution A: PIPETTE 50.00 mL of strontium standard storage solution (4.2.9) into a 200 mL volumetric flask, DILUTE to the mark with water, and MIX well. 1 mL of this solution contains 0.25 mg of strontium.

4.2.11 Strontium standard solution B: PIPETTE 50.00 mL of strontium standard storage solution (4.2.9) into a 500 mL volumetric flask, DILUTE to the mark with water, and MIX well. 1 mL of this solution contains 0.1 mg of strontium.

4.3 Instruments and equipment

Atomic absorption spectrometer with strontium hollow cathode lamp. The instrument shall meet the following conditions:

- Characteristic concentration: in a solution consistent with the matrix of the tested sample solution, the characteristic concentration of strontium shall not be greater than 0.25 µg/mL;

- Precision: use the highest-concentration standard solution to measure the absorbance 10 times, the standard deviation shall not exceed 1.0 % of the average absorbance; use the lowest-concentration standard solution (not a "zero" concentration solution) to measure the absorbance 10 times, the standard deviation shall not exceed 0.5 % of the average absorbance of the highest-concentration standard solution;

- Working curve linearity: divide the working curve into five equal segments according to concentration. The ratio of the absorbance difference of the highest segment to the absorbance difference of the lowest segment shall not be less than 0.7.

4.4 Sample

Process the sample into chips with a thickness of no more than 1 mm.

4.5 Analysis steps

4.5.1 Sample

Weigh the sample (4.4) with a mass (m0) of 0.50 g, accurate to 0.0001 g.

4.5.2 Parallel test

Carry out two tests in parallel and take the average value.

4.5.3 Blank test

Weigh pure aluminum (4.2.1) according to Table 1 to replace the sample (4.5.1), and carry out a blank test along with the sample.

4.5.4 Determination

4.5.4.1 PLACE the sample (4.5.1) into a 250 mL beaker, ADD 15 mL of hydrochloric acid (4.2.5), after the violent reaction stops, ADD 3 ~ 5 drops of hydrogen peroxide (4.2.2), BOIL and STEAM until salt precipitates, COOL down slightly, ADD 3 mL of hydrochloric acid (4.2.5), HEAT until the salts are dissolved, then REMOVE the beaker and COOL down.

4.5.4.2 If there is insoluble matter, filter and wash. PLACE the residue together with the filter paper in a platinum crucible, ASH it (do not burn the filter paper). […]

5.3 Sample

Process the sample into chips with a thickness of no more than 1 mm.

5.4 Analysis steps

5.4.1 Sample

Weigh the sample (5.3) with a mass (m) of 0.20 g, accurate to 0.0001 g.

5.4.2 Parallel test

Carry out two tests in parallel and take the average value.

5.4.3 Determination

5.4.3.1 PLACE the sample (5.4.1) into a 250 mL beaker, ADD 6 mL of hydrochloric acid (5.2.4), ADD a few drops of hydrogen peroxide (5.2.1), HEAT, after the sample is completely dissolved, COOL down.

5.4.3.2 DILUTE to about 20 mL with water, NEUTRALIZE with ammonia water (5.2.3) until the pH of the solution is about 6 (precision pH test paper), ADD 15 mL of hexamethylenetetramine solution (5.2.5), CONTROL the pH of the solution to 6. 5 ~ 7.5, HEAT and BOIL for 1 min, then COOL down to room temperature. ADD 10 mL of copper reagent solution (5.2.6) while stirring, TRANSFER it to a 200 mL volumetric flask (V5), DILUTE to the mark with water, and MIX well. LET STAND for 30 min and carry out dry filtration.

5.4.3.3 PIPETTE 50.00 mL of filtrate (V6) into a 250 mL Erlenmeyer flask, ADD water to approximately 100 mL, ADD 10 mL of ammonia-ammonium chloride buffer solution (5.2.7), ADD 10.00 mL (V0) of magnesium standard solution (5.2.9), ADD 3 ~ 5 drops of chrome black T indicator (5.2.11), TITRATE with Na2EDTA standard titration solution (5.2.10) until the color change nears the end point, ADD 7 mL to 8 mL of absolute ethanol (5.2.2), continue to TITRATE until the solution turns pure blue, which is the end point. RECORD the volume of Na2EDTA standard solution consumed (V4). […]