DETERMINATION OF 6 WATER-SOLUBLE VITAMINS IN A PHARMACEUTICAL FORMULATION BY CAPILLARY ELECTROPHORESIS

A method was developed for the quantitative analysis of six water-solu ble vitamins (thiamine, nicotinamide, riboflavine, pyridoxine, ascorbi c acid and pantothenic acid) in a pharmaceutical formulation, using fr ee solution capillary zone electrophoresis (CZE) in uncoated fused sil ica capillaries and UV detection. The influence of different parameter s, such as the nature of the buffer anionic component and buffer conce ntration on the CZE separation of vitamins was investigated using four vitamins of the B group as model compounds. A good compromise between resolution, analysis time and analyte stability was obtained by use o f a 50 mM borax buffer of pH 8.5. This CZE method was found to be very useful for the separation of more complex samples, a mixture of ten w ater-soluble vitamins being completely resolved in about 10 min. Howev er, cyanocobalamine could not be separated from nicotinamide in this C ZE system, the two compounds being in uncharged form at the pH used. T hese two compounds could easily be resolved by micellar electrokinetic chromatography (MEKC), the anionic surfactant dodecylsulfate being ad ded to the running buffer at 25 mM concentration. In the pharmaceutica l formulation, some excipients were found to be adsorbed to the capill ary surface, giving rise to a progressive decrease of the electroosmot ic flow and consequently to a simultaneous increase of analyte migrati on times. A capillary wash with sodium hydroxide had to be made betwee n successive runs in order to minimize these effects. Good results wit h respect to linearity, precision and accuracy were obtained in the co ncentration range studied for the six vitamins, using nicotinic acid a s internal standard. (C) 1997 Eisevier Science B.V.