DETERMINATION OF 25-HYDROXYVITAMIN-D3 IN HUMAN SERUM BY FLUORESCENCE LABELING AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A method is described for the determination of 25-hydroxyvitamin D3 in human blood serum. The problems of sensitivity and selectivity encountered with previous techniques were avoided by the formation of a highly fluorescent Diels-Alder adduct following solid-phase extraction of the vitamin. After excess of reagent had been eliminated, quantification was achieved by high-performance liquid chromatography. The recovery of the vitamin from serum was 76.4 +/- 1.76%. The precision of the method was determined, and the relative standard deviations were 8.38% at a concentration of 47.0 x 10(-9) mol dm-3, 6.74% at a concentration of 99.8 x 10(-9) mol dm-3 and 3.79% at a concentration of 146.8 x 10(-9) mol dm-3. The detection limit for the adduct was 2.93 x 10(-14) mol injected, for a signal-to-noise ratio of 3:1, and serum concentrations of 0.25 x 10(-9) mol dm-3 could easily be quantified. No interference from endogenous or exogenous substances was observed.