Determination of vitamin C in chemical, pharmaceutical and biological samples by spectrophotometric titrimetry with o-diacetoxyiodobenzoate. Analysis of mixtures of vitamin C with methionine and cysteine or glutathione

Abstract

A method has been developed for the determination of vitamin C in pharmaceutical preparations, foodstuffs and biological fluids based on titrimetry with o-diacetoxyiodobenzoate (o-DIB) with spectrophotometric (λ_max. 600 nm) or visual detection of the end-point using leuco-2,6-dichlorophenolindophenol and potassium iodide as indicator. Sulphur-containing amino acids such as cysteine and glutathione interfere quantitatively and can be masked by cyanoethylation; the cyanoethylated product and methionine have also been determined with o-DIB in the presence of acidified potassium bromide with methyl red as indicator. Procedures are given for the analysis of mixtures of vitamin C with sulphur-containing amino acids. The effect of a number of interferents has also been studied.