HG/T2785-2012 Ammonium Bisulfite for Industrial Use

Determined by visual inspection.

5.2 Determination of Ammonium Bisulfite Content

5.2.1 Principle

In the sample, ammonium bisulfite is oxidized to ammonium bisulfate by hydrogen peroxide. Then, using methyl red-indigo mixed solution as an indicator, titration is performed with sodium hydroxide standard titration solution until the endpoint of yellow-green coloration. The content of ammonium bisulfite is calculated based on the consumption of sodium hydroxide standard titration solution.

response equation ：

NH4HSO3+H2O2→NH4HSO4+H2O

2NH4HSO4+2NaOH→（NH4）2SO4Na2SO4+2H2O

5.2.2 Reagents and Materials

5.2.2.1 Standard titration solution of sodium hydroxide:

5.2.2.2 Methyl Red Ethanol Solution: 1 g/L.

5.2.2.3 Indigo (chemical grade) ethanol solution: 1 g/L.

5.2.2.4 Methyl Red-Indigo Blue Mixed Indicator: Prepared by adding 2 parts of indigo blue ethanol solution to 1 part of methyl red ethanol solution.

5.2.2.5 Hydrogen peroxide solution: 3%;

5.2.2.6 Neutral hydrogen peroxide solution:

Using methyl red-indigo mixed indicator as the indicator, a 3% hydrogen peroxide solution was neutralized with sodium hydroxide standard titration solution until the color changed from red to yellow-green.