Iodimetric method for the determination of sorbic acid in soft drinks

Abstract

An iodimetric method for the determination of sorbic acid in soft drinks is described. The method is based on the quantitative reaction between sorbic acid and N-bromosuccinimide in water-acetic acid medium. A known excess of N-bromosuccinimide is added to brominate sorbic acid, and the excess of N-bromosuccinimide is then allowed to react with iodide to liberate iodine, which is subsequently titrated with standard thiosulphate solution.

The optimum conditions for the bromination were assessed. The recoveries of sorbic acid at concentrations of 36–385 µg ml^–1 ranged from 95 to 104%. The relative standard deviation of ten replicate determinations of sorbic acid in a synthetic sample containing 171 µg ml^–1 of the acid was 2.9%. Interferences from a number of common food additives can be minimised by extracting the sorbic acid with diethyl ether and then back-extracting the acid with sodium hydrogen carbonate solution. The method has been successfully applied to the analysis of various synthetic and real soft drink samples.