Spectrophotometric determination of sulphate for measuring sulphur dioxide in air

Abstract

A simple spectrophotometric method for the determination of low concentrations of sulphate using Sulphonazo III reagent is described. The method involves precipitation of barium sulphate and formation of a blue complex between unreacted barium and Sulphonazo III. The absorbance is inversely proportional to sulphate content and the working range for the method is from 3 to 30 µg (as SO₄^2–) per 5 ml of sample (0.6 × 10^–5 to 6 × 10^–5M). For standard sulphate solutions (0.6–6 µg ml^–1) the standard deviation is less than 0.1 µg ml^–1. The procedure is intended mainly for the determination of sulphur dioxide in ambient air after absorption in dilute hydrogen peroxide.