DETERMINATION OF VITAMIN-B12 IN MULTIVITAMIN MULTIMINERAL TABLETS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AFTER SOLID-PHASE EXTRACTION

A method for the determination of vitamin B12 (cyanocobalamin) in multivitamin-multimineral tablets, containing 3-mu-g of vitamin B12 per tablet, is described. Powdered tablets are extracted with a mixture of ammonium pyrrolidinedithiocarbamate and citric acid in dimethyl sulphoxide and water. The extract is centrifuged and the supernatant is diluted with water before concentration and clean-up by solid-phase extraction using a quaternary amine and a phenyl column in series. The eluate from the solid-phase extraction is analysed by reversed-phase liquid chromatography using a methanol-water gradient with detection at 550 nm. A comparison with the frequently used microbiological method is presented. The validation of the procedure is described in terms of selectivity, linearity, accuracy and precision.