Advantages of paper chromatography as a preparative step in the assay of 1,25-dihydroxyvitamin D.

Ether extraction and paper chromatography were used to separate the main metabolites of vitamin D in plasma [25-(OH), 24,25-(OH)2 and 1,25-(OH)2 vitamin D]prior to radio receptor-assay. The overall procedural loss of the 1,25-(OH)2 vitamin D was 58 +/- 5% (n = 40), corrected for by tracer addition. The sensitivity of the assay was 0.5 fmol/tube, corresponding to 4 pmol/l, and the intra- and inter-assay coefficients of variation were 10.5% and 11.5%, respectively. The range of values measured in healthy controls was 80-200 pmol/l (n = 60), which is in agreement with findings reported in the literature. A comparison of the results of the present procedure with those obtained with a procedure employing C18 purification, disclosed a correlation coefficient of 0.92 (p < or = 0.0001), a slope of 0.89 (p < or = 0.0001) and a small non-significant intercept of 5.0 pmol/l (n = 53).