Separation of retinoids by micellar electrokinetic capillary chromatography

In this study, we have developed a micellar electrokinetic capillary chromatography (MEKC) method with diode-array detection to separate five important retinoids, including retinol, retinal, retinoic acid, retinyl acetate and retinyl palmitate. These very hydrophobic retinoids are successfully separated with phosphate buffer containing sodium deoxycholate (SDC) and Brij 35 as the micellar pseudostationary phase. The effects of SDC and Brij 35 concentration on the migration behavior of the five retinoids are also discussed. The relative standard deviations of the migration times of the retinoids are less than 1.9% in the optimized separation condition. Moreover, a direct extraction method without saponification is employed to extract retinyl esters in pharmaceutical products. The ranges of recoveries are 95%-99% for retinyl esters with less than 2% relative standard deviations. Therefore, retinyl esters in pharmaceutical products can be determined by combining the direct extraction and the MEKC methods.