SPECTROPHOTOMETRIC DETERMINATION OF ASCORBIC-ACID IN PHARMACEUTICAL PRODUCTS WITH THE COPPER(II)-RHODANINE REAGENT

Abstract

A simple method has been developed for the determination of ascorbic acid(AA) in pharmaceutical products by the copper(II)-5-(4-hydroxy-3-methoxybenzilidene) rhodanine reagent. The method is based on the oxidation of AA with the reagent and complexation of copper(I) product with unchanged rhodanine. The red complex soluble in dioxane-water yields an effective molar absorptivity of 2.6 x 10(4) 1.mol-1.cm-1 at 473 nm for AA at an apparent pH of 3.8. Beer's law is obeyed between 6.25 x 10(-6) and 3.75 x 10(-5) mol.dm-3 concentrations of AA with a relative standard deviation of 3.4%. The method has been successfully applied to vitamin C assay in pharmaceutical formulations. Biologically important thiols such as oysteine and glutathione could also be quantified by the same procedure with a molar absorptivity of 1.3 x 10(4) 1.mol-1.cm-1.