GB/T 5686.4-2022Ferromanganese, ferromanganese-silicon, nitrogen-bearing ferromanganese and manganese metal—Determination of phosphorus content—Molybdenum blue spectrophotometric method and bismuth phosphomolybdate blue spectrophotometric method (English PDF)

4.1 Principle

The test portion is decomposed by nitric acid and hydrofluoric acid. Add perchloric acid to evaporate it, until emitting smoke, thereby oxidizing phosphorus into orthophosphoric acid.

Add sodium bisulfite to reduce iron, etc., add ammonium molybdate and hydrazine sulfate to generate phosphomolybdenum blue. At a wavelength of 825 nm, use a spectrophotometer to measure its absorbance, and calculate the mass fraction of phosphorus.

4.2.8 Hydrazine sulfate solution, 1.5 g/L

4.3 Instruments

In the analysis, only common laboratory instruments are used. The one-mark volumetric flasks, graduated pipettes and one-mark pipettes used shall comply with the requirements of GB/T 12806, GB/T 12807 and GB/T 12808, respectively.

4.4 Sampling and Sample Preparation

In accordance with the provisions of GB/T 4010, conduct sampling and sample preparation. The specimens shall all pass the 0.125 mm sieve mesh.

4.5 Analytical Steps

4.5.1 Number of determinations

For the same specimen, conduct at least 2 independent determinations.

4.5.2 Amount of test portion

4.5.3 Blank test

Along with the test portion, carry out a blank test.

4.5.4 Determination

4.5.4.1 Decomposition of test portion

4.5.4.2 Color development and determination

4.5.4.2.1 Slightly cool, remove the watch glass, add about 30 mL of warm water, heat and boil to dissolve the soluble salts. Remove it, dropwise add sodium bisulfite solution (see 4.2.6) to decompose manganese dioxide, etc. Use a medium-speed filter paper to filter it into a 250 mL volumetric flask. Use warm water to wash it, until there is no acidity, cool to room temperature, use water to dilute to the scale and mix it well.

4.5.5 Drawing of calibration curve

4.5.5.1 Drawing of calibration curve of manganese metal with low phosphorus content (mass fraction 0.0030% ~ 0.020%)

4.5.5.1.1 Transfer-take 0 mL, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL, 10.00 mL and 12.00 mL of phosphorus standard solution (see 4.2.11) and place them into a set of 100 mL beakers.

Respectively add 5 mL of perchloric acid (see 4.2.5), heat and evaporate them, until emitting perchloric acid smoke. Remove them and follow 4.5.4.2 for the subsequent operations.

4.5.5.3 Drawing of calibration curve of ferromanganese, ferromanganese-silicon, nitrogen-bearing ferromanganese 4.5.5.3.1 Transfer-take 0 mL, 1.00 mL, 3.00 mL, 5.00 mL, 7.00 mL and 9.00 mL of phosphorus standard solution (see 4.2.10) and place them into a set of 100 mL beakers. Respectively add 5 mL of perchloric acid (see 4.2.5), heat and evaporate them, until emitting perchloric acid smoke. Remove them and follow 4.5.4.2 for the subsequent operations.

4.6 Calculation of Analysis Results

In accordance with Formula (1), calculate the phosphorus content wP in the specimen, expressed in mass fraction (%).

4.7 Allowable Difference

The difference in the intra-laboratory and inter-laboratory analysis results shall be not greater than the allowable difference listed in Table 2. Otherwise, the number of additional measurements and the analysis results shall be determined as specified in Appendix A.

5.1 Principle

The test portion is decomposed by nitric acid and hydrofluoric acid. Add perchloric acid to evaporate it, until emitting smoke, thereby oxidizing phosphorus into orthophosphoric acid. In sulfuric acid medium,

5.2 Reagents and Materials

Unless otherwise specified, only reagents that are confirmed to be analytically pure are used in the analysis. The test water is distilled water or water with an equivalent purity of Grade-3 or above that complies with the provisions of GB/T 6682.

5.2.7 Sodium hydroxide solution, 250 g/L. Stored in plastic bottles.

5.2.8 Sodium thiosulfate solution, 10 g/L

Weigh-take 1.0 g of sodium thiosulfate and 2.0 g of anhydrous sodium sulfite, dissolve it in 100 mL of water, and mix it well. Prepare it right before use.

5.2.9 Bismuth nitrate solution, 30 g/L

Weigh-take 30 g of bismuth nitrate [Bi(NO3)3 - 5H2O] and dissolve it in 100 mL of nitric acid (see 5.2.1). After it is completely dissolved, add 900 mL of water and 4 g of urea, and mix it well.

5.2.14 Phosphorus standard solution, 100 µg/mL.

5.2.16 Phosphorus standard solution, 2.5 µg/mL

Weigh-take 25.00 mL of phosphorus standard solution (see 5.2.14) into a 1,000 mL volumetric flask. Use water to dilute to the scale and mix it well. 1 mL of this solution contains 2.5 µg of phosphorus.

5.2.17 Phenolphthalein solution, 1 g/L

Weigh-take 0.1 g of phenolphthalein into a 150 mL beaker and add 50 mL of ethanol (950 g/L) to dissolve it. Add water to dilute to 100 mL and mix it well.

5.3 Instruments

In the analysis, only common laboratory instruments are used. The one-mark volumetric flasks, graduated pipettes and one-mark pipettes used shall respectively comply with the requirements of GB/T 12806, GB/T 12807 and GB/T 12808.

5.4 Sampling and Sample Preparation

In accordance with the provisions of GB/T 4010, conduct sampling and sample preparation. The specimens shall all pass the 0.125 mm sieve mesh.

5.5 Analytical Steps

5.5.1 Number of determinations

For the same specimen, conduct at least 2 independent determinations.

5.5.2 Amount of test portion

In accordance with Table 3, weigh-take the specimens, accurate to 0.0001 g.

5.5.3 Blank test

Along with the test portion, carry out a blank test.

5.5.4 Determination

5.5.4.1 Decomposition of test portion

5.5.5 Drawing of Calibration Curve

5.5.5.1 Drawing of calibration curve of manganese metal with low phosphorus content (mass fraction 0.0030% ~ 0.020%)

5.5.5.2.1 Transfer-take 0 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL, 5.00 mL and 6.00 mL of phosphorus standard solution (see 5.2.15) and place them into a set of 50 mL beakers.

Respectively transfer 1.00 mL of ferric ammonium sulfate solution (see 5.2.13) into them, add 5.00 mL of sulfuric acid (see 5.2.4), use water to adjust the volume to about 20 mL, add 5 mL of sodium thiosulfate solution (see 5.2.8), mix them well, then, add 5 mL of bismuth nitrate solution (see 5.2.9), use water to purge the wall of the beakers,

5.5.5.3 Drawing of calibration curve of ferromanganese, ferromanganese-silicon, nitrogen-bearing ferromanganese 5.5.5.3.1 Transfer-take 0 mL, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL and 10.00 mL of phosphorus standard solution (see 5.2.15) and place them into a set of 50 mL beakers. Respectively transfer 1.5 mL of ferric ammonium sulfate solution (see 5.2.13) into them, add 5.00 mL of sulfuric acid (see 5.2.4), use water to adjust the volume to about 20 mL, add 5 mL of sodium thiosulfate solution (see 5.2.8), mix them well, then, add 5 mL of bismuth nitrate solution (see 5.2.9), use water to purge the wall of the beakers, and shake them well. Add 5 mL of ammonium molybdate solution (see 5.2.10), use water to purge the wall of the beakers, and shake them well; add 5 mL of ascorbic acid solution (see 5.2.11) and mix them well; use water to dilute them to the scale and mix them well. Let them stand for 15 minutes.

5.5.5.3.2 Transfer the test solutions (see 5.5.5.3.1) into 0.5 cm cuvettes. At a wavelength of 700 nm, use water as a reference to zero the spectrophotometer, and measure their absorbance.