Quantitation of sodium hydrogensulfite in parenteral samples by a flow-injection method

Sodium hydrogen sulfite reacts with 5,5′-dithiobis(2-nitrobenzoic acid) at pH 6.0 to produce a colored 2-nitrothiobenzoate ion with maximum absorbance at 410 nm. The absorbance varies linearly with concentration over the range of 1 ng-1 μg of sodium hydrogensulfite injected and the absolute detection limit is 0.3 ng. The relative standard deviation at 10 ng or greater is typically 1.5%. Matrix components in pharmaceutical parenteral solutions (e.g., amino acids, drugs, dextrose, buffers) do not interfere.