A nonaqueous electrochromatographic reversed-phase separation method for retinyl esters using continuous bed columns has been developed. The Ž packing material was C modified material large-pore silica 5 m Nucleosil 4000 30 ˚.
A . The continuous bed columns were prepared by sol᎐gel bonding in 180 m inside diameter fused silica capillaries. The mobile phase consisting of 2.5 mM Ž . lithium acetate in N, N-dimethylformamide-acetonitrile-methanol 2 q 7 q 1, vrv gave rise to an electroosmotic flow of 1 mmrs at 350 Vrcm and 40ЊC. Using a 36 cm effective length column separation of the commercially available and synthe-Ž sized standards all-trans-retinyl acetate, palmitate, heptadecanoate, stearate, . oleoate, and linoleoate was obtained within 12 min. Separation of isomeric retinyl Ž . palmitate 13-cis-and all-trans-retinyl palmitate was also obtained. The selectivity was found to be temperature dependent in the temperature range investigated Ž . Ž . 30᎐60ЊC . The within-day and between-day variations n s 3 of retention times Ž . of all-trans-retinyl palmitate were 0.2% relative standard deviation RSD and -2.5% RSD, respectively. Further, the within-day and between-day variations Ž . n s 3 of peak areas were in both cases -4% RSD using injection. The column examined was stable for more than 1 month of extensive use. Liver extracts from arctic seal were analyzed.