HG/T 2784-2012 Ammonium Sulfite for Industrial Use

In this standard, reagents and water used, unless otherwise specified, refer to analytical grade reagents and water meeting the requirements of GB/T 6682 (Grade III water). Standard titration solutions, preparations, and products used in the tests, unless otherwise specified, shall be prepared in accordance with the provisions of GB/T 601 and GB/T 603.

4.2 Determination of Ammonium Sulfite

4.2.1 Appearance

Determined by visual inspection.

4.2.2 Determination of Ammonium Bisulfite Mass Fraction

4.2.2.1 Principle

In neutral or weakly acidic solutions, iodine oxidizes ammonium sulfite and ammonium bisulfite in the test solution to ammonium sulfate and ammonium bisulfate, respectively. A starch solution is then used as an indicator. The excess iodine is titrated with a sodium thiosulfate standard titration solution until the blue color just fades, marking the endpoint. The mass fraction of ammonium bisulfite monohydrate is calculated based on the consumption of the ammonium hexasulfate standard titration solution.

The reaction is:

（NH4）2SO3+I2+H2O→（NH4）2SO4+2HI

NH4SO3SO3+I2+H2O→NH4SO42HI

          2NaS2O3+I2→Na2S4O6+2NaI

4.2.2.2 Reagents

4.2.2.2.1 Iodine solution: 254 g/L

4.2.2.2.2 Sodium thiosulfate standard titration solution: c(Na2S2O3) = 0.1 mol/L.

4.2.2.2.3 Starch indicator solution: 10g/L.

4.2.2.3 Analysis Steps

Weigh 0.10g to 0.15g of the sample using the difference subtraction method with precision to 0.0001g. Transfer the sample to a 250ml iodine volumetric flask containing 25.00ml iodine solution (4.2.2.2.1) and shake thoroughly. Titrate with sodium thiosulfate standard titration solution (4.2.2.2.2) until the solution turns pale yellow. Add 2ml of starch indicator solution (4.2.2.2.3) and continue titration until the blue color just fades to the endpoint. Retain solution A for determining the mass fraction of ammonium sulfate.

A blank test was performed simultaneously with the aforementioned determination.