On-Line Concentration Methods for Analysis of Fat-Soluble Vitamins by MEKC

A micellar electrokinetic chromatography method was developed for the simultaneous determination of three fat-soluble vitamins with UV detection. Several factors, such as the composition, concentration and pH of the background solution, different additives in the background solution, were optimized. Three on-line concentration methods, namely, sweeping, field-enhanced sample injection and pressure-assisted field-enhanced sample injection (PA-FESI), were utilized to improve the detection sensitivities of the analytes and compared. Of the three methods, PA-FESI can achieve the largest concentration efficiency for the fat-soluble vitamins. In the method, enhancement in the detection sensitivities of fat-soluble vitamins was in the range 42 to 103-fold, as compared to the usual injection method. The PA-FESI was used as an on-line concentration method for the determination of fat-soluble vitamins in multivitamin tablets and vitamin E soft capsules.