GB/T 23940-2021Analytical methods of persulfate products for industrial use (English PDF)

5.1 Principle

Potassium iodide reacts with persulfate to generate free iodine. In a weakly acidic solution, use starch as an indicator and use sodium thiosulfate standard titration solution for titration.

5.2 Reagents or materials

5.2.1 Potassium iodide.

5.2.2 Glacial acetic acid solution: 1+2.

5.2.3 Sodium thiosulfate standard titration solution: c(Na2S2O3) ~ 0.1 mol/L.

5.2.4 Starch indicator solution: 10 g/L (the use period is about two weeks).

5.3 Test steps

Weigh about 0.3 g of the sample, accurate to 0.000 2 g; place it in a 250 mL iodine flask.

Add 30 mL of water to dissolve it; add 4 g of potassium iodide; cover the bottle; shake well; seal it with water. Place in the dark for 30 min; add 2 mL of glacial acetic acid solution and 25 mL of water; use sodium thiosulfate standard titration solution for Carbon dioxide-free water.

6.2 Instruments and equipment

Acidity meter: accuracy 0.02 pH unit. Equipped with glass electrodes, saturated calomel electrodes or combination electrodes.

6.3 Test steps

Weigh 5.00 g ± 0.01 g of the sample; place it in a 250 mL beaker; add 100 mL of carbon dioxide-free water at about 25 °C; after the sample is completely dissolved, follow the steps specified in 8.3 of GB/T 23769-2009.

7.1 Principle

Same as Chapter 3 of GB/T 3049-2006.

7.2 Reagents or materials

Same as Chapter 4 of GB/T 3049-2006.

7.3 Instruments and equipment

7.3.1 Porcelain evaporating dish: volume 50 mL.

7.3.2 Constant temperature water bath.

7.3.3 Spectrophotometer: equipped with a 4 cm cuvette.

7.4 Test steps

7.4.2 Preparation of test solution A Weigh an appropriate amount of sample (10 g for sodium persulfate and potassium persulfate, and 20 g for ammonium persulfate), accurate to 0.01 g; place in a porcelain evaporating dish; add a small amount of water to moisten; cover with a watch glass; decompose by heating on a constant temperature water bath and evaporate to dryness.

7.4.1 Drawing of the standard curve

According to the steps specified in 6.3 of GB/T 3049-2006, use a 4 cm cuvette to draw a standard curve with an iron content of 10 µg ~ 100 µg.

Slowly heat on the electric furnace until a large amount of white smoke begins to escape; cool down. Use water to dissolve the residue; transfer it all to a 100 mL volumetric flask; use water to dilute to the mark; shake well. This solution is the test solution A, which is used for the determination of iron content and heavy metal content.

Use a pipette to pipette 1 mL of chloride standard solution prepared according to the requirements of HG/T 3696.2; place it in a 100 mL volumetric flask; use water to dilute to the mark; shake well. Formulate the solution when needed.

8.3 Test steps

Weigh an appropriate amount of the sample (0.50 g ± 0.01 g for sodium persulfate and potassium persulfate, and 2.00 g ± 0.01 g for ammonium persulfate); place it in a 50 mL beaker; add an appropriate amount of water to dissolve it. Transfer all the solution to a 50 mL colorimetric tube; add 1 mL of 95% ethanol, 1 mL of nitric acid solution and 2 mL of silver nitrate solution; use water to dilute to the mark; shake gently; let it stand for 10 min; compare it with the standard turbidimetric solution under a black background.

The standard turbidimetric solution is based on the chloride content specified in the product standard. Use a pipette to pipette the specified amount of chloride standard solution; treat it in the same way as the sample at the same time.

9.1 Instruments and equipment

9.1.1 Weighing bottle: phi50 mm × 30 mm.

9.1.2 Electrothermal constant-temperature drying oven: the temperature can be controlled at 100 °C ± 2 °C.

9.1.3 Vacuum pump.

9.1.4 Vacuum drying box: the temperature can be controlled within the temperature range specified in Table 1.

9.2 Test steps

Use a weighing bottle that has been dried to a constant mass according to the drying conditions specified in Table 1, to weigh about 5 g of the sample, accurate to 0.000 2 g.

Shake the weighing bottle slowly to make the thickness of the sample uniform; place it in a drying box (if a vacuum drying box is used for drying, use a vacuum pump to draw to vacuum and keep the vacuum degree); place it for the drying time specified in Table 1; take it out; place it in a desiccator; cool to room temperature; weigh.

HG/T 3696.2; place it in a 100 mL volumetric flask; use water to dilute to the mark; shake well. Formulate the solution when needed.

10.3 Test steps

Weigh an appropriate amount of sample (10.50 g ± 0.01 g for sodium persulfate and ammonium persulfate, and 1.50 g ± 0.01 g for potassium persulfate); place it in a 50 mL beaker; add an appropriate amount of water to dissolve it, and transfer it all to a 50 mL colorimetric tube; add 0.5 mL of phosphoric acid and 1 mL of silver nitrate solution; use water to dilute to the mark; shake well. Let it stand for 5 min and compare it with the standard colorimetric solution.

Measure the standard colorimetric solution by weighing 0.50 g ± 0.01 g of the sample and the manganese content specified in the product standard; use a pipette to pipette a specified amount of manganese standard solution; treat it in the same way as the sample.

11.1 Principle

When the sample is in an acidic medium with a pH of 3 ~ 4, add saturated hydrogen sulfide aqueous solution to convert heavy metals into sulfides; compare the dark color with the standard colorimetric solution by visual colorimetry.

11.2 Reagents or materials

11.2.2 Glacial acetic acid solution: 1+2.

11.2.3 Saturated hydrogen sulfide water: prepare this solution before use.

11.2.4 Sodium sulfide solution.

11.2.5 Lead standard solution: 1 mL of solution contains 0.010 mg of lead (Pb). Pipette 1 mL of the lead standard solution that is prepared according to HG/T 3696.2; place it in a 100 mL volumetric flask; use water to dilute to the mark; shake well. Formulate the solution when needed.

11.3 Test steps

Pipette 20 mL of the test solution A (see 7.4.2); put it into a 50 mL colorimetric tube; add 1 ~ 2 drop(s) of phenolphthalein indicator solution; use ammonia solution to neutralize it until the solution is reddish (pH ~ 7); add water to about 25 mL; add 0.5 mL of glacial acetic acid solution, 10 mL of saturated hydrogen sulfide water or 2 drops of sodium sulfide solution; use water to dilute to the mark; shake well. Let it stand for 10 min and compare it with the standard colorimetric solution.

Prepare the standard colorimetric solution by pipetting 10 mL of test solution A (see 7.4.2) and the heavy metal content as specified in the product standard; pipette the specified amount of lead standard solution; prepare it in the same way as the sample at the same time.

12.1 Principle

In alkaline solution, Nessler's reagent reacts with ammonia to generate yellow to brown-red insoluble compounds; compare it with standard colorimetric solutions by visual colorimetry.

12.2 Reagents or materials

12.2.2 Nessler's reagent.

12.2.3 Ammonium standard solution: 1 mL of solution contains 0.010 mg of ammonium (NH4). Pipette 1 mL of the ammonium standard solution that is prepared according to

12.2.1 Sodium hydroxide solution: 100 g/L

HG/T 3696.2; place it in a 100 mL volumetric flask; use water to dilute to the mark; shake well. Formulate the solution when needed.

12.3 Test steps

Weigh 1.00 g ± 0.01 g of the sample; place it in a 50 mL beaker; add an appropriate amount of water to dissolve it; transfer all the solution to a 100 mL volumetric flask; use water to dilute to the mark; shake well.

Use a pipette to pipette 1.00 mL of the above test solution; put it in a 50 mL colorimetric tube; add water to about 25 mL; add 2 mL of sodium hydroxide solution and 2 mL of Nessler's reagent; use water to dilute to the mark; shake well; compare it with the standard colorimetric solution.

The standard turbidimetric solution is based on the ammonium salt content specified in the product standard. Pipette the specified amount of ammonium standard solution; treat it in the same way as the sample at the same time.