Microemulsion electrokinetic chromatography in suppressed electroosmotic flow environment - Separation of fat-soluble vitamins

Microemulsion electrokinetic chromatography (MEEKC) was carried out in a pH 2.5 phosphate buffer to effectively suppress the electroosmotic flow (EOF) . With 66.6% (w/w) 25 mM phosphate buffer pH 2.5, 20.0% (w/w) 2-propanol, 6 .6% (w/w) l-butanol, 6.0% (w/w) sodium lauryl sulphate (SDS), and 0.8% (w/w ) n-octane as the separation medium, the fat-soluble vitamins ii palmitate, E acetate, and D-3 were baseline separated within II min. With strongly su ppressed EOF, the polarity of the separation voltage was reversed (positive electrode at the outlet); the n-octane micro droplets surrounded by negati vely charged SDS molecules migrated towards the detector. The aqueous part of the microemulsion was modified with 20% (w/w) 2-propanol to improve part ition between the n-octane phase and the surrounding aqueous medium. The fa t-soluble vitamins were separated in order of decreasing hydrophobicity wit h a high migration time stability (repeatable within 0.1% RSD). Excellent a ccuracy and precision were obtained when the system was applied for the det ermination of vitamin E acetate in commercial vitamin tablets; quantitative data corresponded to 97.0% of label claim, intra-day results varied within 1.72% RSD (n=6), and inter-day results varied within 3.22% RSD (n=5). (C) 2000 Elsevier Science B.V. All rights reserved.