The determination of ascorbic acid in urine with phospho-18-tungstic acid

Abstract

THE use of 2:6-dichlorophenolindophenol as an indicator in the quantitative estimation of ascorbic acid is open to the objection that the reaction is non- specific in that phenols and thiol compounds (especially cysteine) reduce the reagent. At PH 3 the action of phenols is suppressed or delayed [Johnson and Emmerie and van The method, as worked out by them, whilst yielding more highly accurate results requires several hours (overnight) for completion. In all cases the end-point of the reaction is far from clear and varies somewhat with the speed of titration.