Simultaneous Determination of Endogenous Retinoic Acid Isomers and Retinol in Human Plasma by Isocratic Normal-Phase HPLC with Ultraviolet Detection

We describe a rapid and simple procedure for the simul-taneous quantitation of endogenous 13-cis-retinoic acid, all-trans-retinoic acid, and retinal by isocratic normal-phase HPLC with ultraviolet detection, in 0.5 mL of human plasma. A silicaadsorptioncolumn was eluted with n-hex-ane:2-propanol:acetic acid (200:0.7:0.135 by vol) at 0.9 mL/min, and the effluent monitored at 350 nm. The aroti-noid ethylsuttonic acid Ro 15-1570 was used as the inter-nal standard. High sensitivity, allowing quantitation of physiological concentrations, was achieved, particularly for the retinoicacid isomers. The detection limitswere 0.5 1g/L in plasma for both 13-cis- and trans-retinoic acid, and 10 g/L for retinal. The CVs for between-day deter-minations of the lowest quality-controlconcentration (n = 12) were 4.8 % for 13-c!s-retinoic acid, 3.4 % for trans