Ultraviloet spectrophotometric determination of sulfite with hydrobromic acid

Abstract

A new and rapid spectrophotometric method for the determination of sulfite was investigated. It was found that sulfite solution has an absorption maximum at 276 nm in the presence of acid such as sulfuric, perchloric or phosphoric acid, and has a intense absorption maximum at about 285 nm or 300 nm in the presence of hydrochloric or hydrobromic acid respectively. The absorbance was greater with hydrobromic acid than with hydrochloric acid. Recommended procedure is as follows. In 25 ml volumetric flask, the sample solution and 10 ml of 7.5N hydrobromic acid were added and diluted to 25 ml with water. The absorbance of the solution was measured at the wavelength of 300 nm with 10 mm cell against water. By this method, the sulfite in the range from 0.2×10^-4 M to 4×10^-4 M {(32640)μg/25 ml as sulfur dioxide} was accurately determined. The variation coefficient was 0.5% at the sulfite level of 2×10^-4 M. Fe(III), Hg(II), Pb(II), NO₂^- and VO₃^- interfered with the determination of sulfite.