AN IMPROVED PROTOCOL FOR DETERMINING RATIOS OF RETINOL-D(4) TO RETINOL ISOLATED FROM HUMAN PLASMA

An improved protocol for assessing vitamin A status in humans using st able isotope dilution is described. Human subjects were given an oral dose of retinyl-d4 acetate, and blood specimens were collected after a period of pseudoequilibration. After the precipitation of proteins, t he plasma was extracted with hexane and partitioned against acetonitri le. Retinol was isolated from the acetonitrile fraction using HPLC, an d the retinol was converted to its tert-butyldimethylsilyl ether and a nalyzed by gas chromatography/mass spectrometry using selected-ion mon itoring. The new method allows for more rapid isolation of retinol fro m plasma with fewer interferences than were seen in our earlier work. Significant improvements in the reliability, sensitivity, and precisio n of the method have been obtained in the present study, and these imp rovements should allow for the use of smaller doses of isotopically la beled vitamin A for evaluation of the vitamin A status of human popula tions.