Improved extraction methods for avoiding the interference of copper in theLC determination of ascorbic acid in multivitamin-mineral tablets

A rapid sample extraction procedure for the determination of ascorbic acid (AA) by high performance liquid chromatography (HPLC) in multivitamin-miner al formulations containing interfering copper has been developed. The metho d takes special precautions to prevent degradation of AA in contact with hi gh concentrations of interfering elements such as copper. Sample preparatio n involved addition of pyrogallol, citric acid solution and short time extr action (5 min) under an atmosphere of nitrogen to prevent oxidation of AA. Another sample cleanup based on extraction of the multivitamin-mineral tabl et with the extraction solution as described above, but with addition of st rong cation exchange sorbent, was also developed. The copper and other mine rals in the formula were retained on an ion exchange sorbent and thus repre sses the speed of oxidation of AA. Extracts of multivitamin-mineral tablets were analyzed by ion-pair reversed phase HPLC and UV-diode array detection . Ten multivitamin Formulations containing copper were analyzed by the two proposed methods. The analytical results of AA obtained using the simple sa mple extraction method and the method involving addition of cation exchange were 89-115% and 95-112%, respectively, of declared concentrations. The pa rameters for the validation of the methods are given. (C) 2001 Elsevier Sci ence B.V. All rights reserved.