Analysis of vitamin formulations by electrokinetic chromatography utilizing tetradecylammonium ions as the pseudostationary phase

A recently proposed method for the separation of fat-soluble vitamins by el ectrokinetic chromatography was further developed and investigated in the p resent study. The separation medium consisted of acetonitrile-water (80:20 v/v) and contained XO mM tetradecylammonium bromide (TDA(+)); the content o f acetonitrile served to maintain the hydrophobic vitamins dissolved during electrophoresis, while the TDA+ ions served as the pseudostationary phase. With the cathode placed at the outlet of the capillary, the fat-soluble vi tamins were separated based on different hydrophobic interactions to the TD A+ ions and migrated in order of decreasing hydrophobicity prior to the ele ctroosmotic flow. Migration time stability was significantly enhanced by th e addition of 4 mM berate to the separation medium. The separation system w as validated for the determination of vitamin E acetate in commercial table ts; quantitative results deviated by less than 3.5% from specified values, varying by less than 2.5% relative standard deviation (RSD) for within-day experiments, and by less than 6.5% RSD during between-day experiments;The s eparation system was compatible with injection solvents ranging in polarity from water to tetrahydrofuran, and was even capable of separating the wate r-soluble vitamins B-1, B-2, B-12, and nicotinamide.