HG/T2785-2012 Ammonium Bisulfite for Industrial Use
5.3.5 Allowable Difference
The arithmetic mean of parallel determination results was taken as the final determination result.
The absolute error of parallel determination results does not exceed 0.35%.
5.4 Total Ammonium Content
The sum of ammonium sulfite and ammonium bisulfite expressed as mass percentage (X3) is calculated according to Equation (3):
X3=X1+X2…………………………（3）
Where: X1 — measured content of ammonium bisulfite,%;
X2 — Measured content of ammonium sulfite,%
5.5 Ammonium bisulfite/ammonium sulfite ratio
The ratio of ammonium sulfite to ammonium sulfite expressed as a percentage by mass (X4) is calculated according to Equation (4):
……………………（4）
Where: X1 — measured content of ammonium bisulfite,%;
X2 — Measured content of ammonium sulfite,%
5.6 Determination of Ammonium Thiosulfate Content
5.6.1 Principle
The sample was titrated with ammonium thiosulfate in a pH 5–6 solution using starch solution as the indicator and formaldehyde solution as the masking agent. The ammonium thiosulfate content was calculated based on the iodine solution dosage.
response equation ：
2（NH4）2S2O3+I2→（NH4）2S4O6+2NH4I
