title: Simultaneous determination of 25-hydroxy- and 1,25-dihydroxyvitamin D from a single sample by dual-cartridge extraction.
abstract: With this dual-cartridge system we extract 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] from a single serum sample by using a nonpolar octadecylsilanol silica cartridge to adsorb the vitamin D metabolites and other nonpolar substances; the polar substances wash through the cartridge. The eluted material is then applied to a second alkylamine cartridge, which adsorbs the relatively polar hydroxylated metabolites; the less-polar substances are washed from the second cartridge. Elution from the second cartridge purifies and also separates 25(OH)D and 1,25(OH)2D with analytical recoveries near 90%. The monohydroxyl metabolites are determined by "high-performance" liquid chromatography (HPLC); the dihydroxyl metabolites are further purified by HPLC and determined by radioreceptor assay according to established procedures. Mean (+/- SD) winter normal values (34 subjects of both sexes; blood drawn in mid-April) were 18 +/- 5 micrograms/L for 25(OH)D and 25 +/- 7 ng/L for 1,25(OH)2D. In nine laboratory volunteers, the mean increase in the serum 25(OH)D3 value 5 h after ingestion of 50 micrograms of 25-hydroxycholecalciferol (Calderol) was 9 (SD 4) micrograms/L.
mesh_terms: D000042:Absorption; D000818:Animals; D002112:Calcifediol / Q000097:blood / Q000302:isolation & purification*; D002117:Calcitriol / Q000097:blood / Q000302:isolation & purification*; D002645:Chickens; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005260:Female; D005387:Finland; D006801:Humans; D008297:Male; D012016:Reference Values; D012621:Seasons; D013781:Texas
chemical_list: D002117:Calcitriol; D002112:Calcifediol