Flow injection determination of sulfite based on the oxidation of phosphonic acid with sulfite

Abstract

Rapid determination of sulfite was carried out by flow injection method. A sulfite solution was mixed with both a phosphonate reagent solution and an acidic molybdenum (V) -molybdenum (VI) reagent solution. In a reaction coil (PTFE, 0.5 mm i. d. 10 m, heated at 140°C), phosphonate was oxidized with sulfite and the resultant orthophosphate allowed to react with the molybdenum reagent to produce a heteropoly blue complex. The absorbance of the heteropoly blue complex was monitored at 800 nm. The standard sample could be measured in a working range of 1 × 10^-4 to 1 × 10^-2 M (NaHSO₃) at a sampling rate of 60 samples h ^-1. Detection limit (S/N=2) was 2× 10^-5 M. The precision (RSD, ten times injection) was 2% for sulfite of 4 × 10^-3 M.