Determination of Retinyl Esters and Retinol in Serum or Plasma by Normal- Phase Liquid Chromatography: Method and Applications

Retinol and retinyl esters are measured in serum or plasma samples by gradient, normal-phase, adsorption “high-per-formance ” liquid chromatography, with ultraviolet detection at 325 nm. The four major circulating retinyl esters in humans (esters of palmitate, stearate, oleate, and linoleate) are co-eluted as a single peak. Retinyl acetate is included as an Internal standard, to correct for variable recovery. Retinol values so measured correlated well (r = 0.88) with those by a widely used reversed-phase chromatographic technique (Clin Chem 1983;29:708-1 2). The mean retinol concentra-tion was 570 (SEM 17) g/L and the mean for retinyl esters was 33 (SEM 4) g/L as determined in samples from 88 fasting young adults. Concentrations of retinol in plasma as low as 50 p.g/L can be detected in 100-.tL samples, as can 10 ig of retinyl esters per liter. Using this method, w