HG/T2785-2012 Ammonium Bisulfite for Industrial Use

The arithmetic mean of parallel determination results was taken as the final determination result.

The absolute error of parallel determination results does not exceed 0.15%.

5.3 Determination of Ammonium Sulfite Content

5.3.1 Principle

In neutral or weakly acidic solutions, iodine oxidizes ammonium bisulfite and ammonium sulfite in the test solution to ammonium bisulfate and ammonium sulfate, respectively. Excess iodine is then titrated with ammonium thiosulfate standard titration solution using starch as an indicator. The ammonium sulfite content is calculated by comparing the sodium thiosulfate standard titration solution consumption with the sodium hydroxide standard titration solution consumption during ammonium bisulfite determination.

response equation ：

NH4HSO3+I2+H2O→NH4SO4+2HI

（NH4）2SO3+I2+H2O→（NH4）2SO4+2HI

2Na3S2O3+I2→Na2S4O6+2NaL

5.3.2 Reagents and Materials

5.3.2.1 Standard titration solution of sodium thiosulfate: c(Na2S2O3) = 0.1000 mol/L.

5.3.2.2 Iodine standard titration solution: c(1/2I2) = 0.1 mol/L;

5.2.2.3 Starch solution: 10 g/L.