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

A simple and rapid spectrophotometric method for the determination of sulfu r 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 metho d obeys Beer's law in the range 0-24 mu g of SO2 in an overall aqueous volu me of 25 mi. The relative standard deviation is 2.6% (n = 10) at 12 mu g of sulfur dioxide. The molar absorptivity is calculated to be 4 x 10(4) 1 mol (-1) cm(-1) with the correlation coefficient of 0.999. The compatibility of the proposed method with several known absorbing solutions for sulfur diox ide is evaluated. The effect of interfering gases on the determination is d iscussed. The method has been applied for the determination of SO2 in the v icinity of furnaces using coal and furnace oil as fuels and also in laborat ory 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]. (C) 2000 Elsevier Science B.V. All rights reserved.