HG/T2785-2012 Ammonium Bisulfite for Industrial Use

5.6.2.1 Formaldehyde

5.6.2.2 Sodium acetate

5.6.2.3 Glacial acetic acid

5.6.2.4 Ice acetic acid-sodium acetate buffer solution: (pH approximately equal to 6)

Weigh approximately 100 g of sodium acetate (CH3COONa·3H2O), dissolve it in water, add 5.7 mL of glacial acetic acid, and dilute to 1000 mL.

5.6.3 Determination

Weigh approximately 13 g of the sample (with precision to 0.0002 g), place it in a 250 mL iodometric flask containing 10 mL formaldehyde, shake well, and let stand for 3 minutes. Add 20 mL buffer solution and 2 mL starch solution, then add ice cubes. Titrate with iodine standard titration solution (5.3.2.2) until blue color develops.

5.6.4 Presentation of Analysis Results

The ammonium thiosulfate content expressed as a percentage by mass (X6) is calculated according to Equation (5):

  ……………………（5）

Where: V — volume of iodine standard titration solution consumed during titration, mL;

         c—Actual concentration of iodine standard titration solution, mol/L

         m — the mass of the sample, in grams;

0.1482 — the mass of ammonium thiosulfate expressed in grams, equivalent to 1.00 mL of iodine standard titration solution.