Differential Electrolytic Potentiometric Titration of Vitamin C in Pharmaceutical Preparations

SHEIKHA M. AL-GHANNAM* AND ABEER M. AL-OLYAN

Girls College of Science, Department of Chemistry, P.O. Box 838, Dammam-31113, Saudi Arabia

(Received: March 29, 2005; Accepted: June 7, 2005)

ABSTRACT

   The application of direct current differential electrolytic potentiometry for the aqueous titration of vitamin C has been investigated.  The reaction of vitamin C with C e (IV) is fast enough to permit its direct titration in 0.09 M sulfuric acid media. C erium ammonium sulfate was used as a titrant and a couple of platinum electrodes as an indicating system. Titration curve shapes obtained are almost symmetrical with sharp peaks. The optimum current density was found to be 0.65 μA cm-2. The procedure was applied successfully to the determination of vitamin C in commercial tablets, capsules as well as in juice in the concentrations of 0.02~10 ppm. The results of this study were favorably compared statistically with those obtained with official methods.

Key words: differential electrolytic potentiometry, oxidation titrimetry, vitamin C , cerium (IV), pharmaceutical preparations