Complexometric determination of citric acid with copper

A method is presented in which citrate is determined by complexation with excess of copper(II), followed by back-titration with EDTA. Small amounts of citrate can be determined by this method in the presence of large amounts of most organic acids present in natural products. Interfering reductants are removed by treatment with permanganate, amino-acids with nitrous acid, and metal ions with a cation-exchange resin. The indicator used for end-point detection is Szechromotrope, 4,4'-sulphonyl-bis(azobenzene) dichromotropic acid.