An indirect method for the determination of sulfur dioxide using Methyl Red

Abstract

A simple and rapid spectrophotometric method for the determination of sulfur dioxide is described. The method is based on the reaction between sulfur dioxide and a known excess of bromine. The unreacted bromine is determined based on its ability to bleach the dye Methyl Red quantitatively. The method obeys Beer’s law in the range 0–24 μg of SO 2 in an overall aqueous volume of 25 ml. The relative standard deviation is 2.6% ( n=10) at 12 μg of sulfur dioxide. The molar absorptivity is calculated to be 4×10 4 l mol −1 cm −1with the correlation coefficient of 0.999. The compatibility of the proposed method with several known absorbing solutions for sulfur dioxide is evaluated. The effect of interfering gases on the determination is discussed. The method has been applied for the determination of SO 2 in the vicinity of furnaces using coal and furnace oil as fuels and also in laboratory fume cupboard. The results obtained are comparable to the standard West and Gaeke Method [P.W. West, G.C. Gaeke, Anal. Chem. 28 (1956) 18161].