DETERMINATION OF RETINOIDS BY REVERSED-PHASE CAPILLARY LIQUID-CHROMATOGRAPHY WITH AMPEROMETRIC ELECTROCHEMICAL DETECTION

A method for separating and detecting retinoids by reversed-phase capi llary liquid chromatography with amperometric electrochemical detectio n is described Packed columns with an inner diameter of 180 mu m were employed for the separation using a C-18 stationary phase and a mobile phase containing acetonitrile-water-methanol (65:32.5:2.5, v/v/v) wit h 1% tetrabutylammonium perchlorate and 0.174 M acetate buffered at pH 5. The detection cell consisted of a carbon fiber barrel electrode he ld at 0.9 V versus an Ag/AgCl reference. Injection volumes of 2 mu l p roduced detection limits of 2.73, 0.472, 0.428, and 0.267 fmol (or 410 , 64.1, 60.9, and 38.2 pg ml(-1)) for 13-cis-retinoic acid, all-trans- retinoic acid, retinaldehyde, and retinol, respectively. This represen ts an improvement in detection limits of at least three orders of magn itude for similar analyses using liquid chromatography and UV absorban ce detection. The detector signal was linear over two orders of magnit ude of analyte concentration. Retinoid concentrations in bovine serum were determined and found to be in good agreement with previously repo rted values.