DETERMINATION OF 22-OXACALCITRIOL, A NEW ANALOG OF 1-ALPHA,25-DIHYDROXYVITAMIN D-3, IN HUMAN SERUM BY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

A sensitive and specific liquid chromatographic-mass spectrometric ass ay has been developed for the determination of 22-oxacalcitriol (OCT), which is a new analog of 1 alpha,25-dihydroxyvitamin D-3. The analyte was isolated from serum by two solid-phase extraction steps on a C-18 cartridge and NH2 cartridge. The recovery of OCT through two extracti on steps was more than 90%. A related substance (ED-94), i.e. OCT with the side-chain shortened by one carbon, was used as an internal stand ard. Extracts were chromatographed on a C-18 reversed-phase column int erfaced to the electrospray ionization source. The mass spectrometer w as operated in the positive-ion mode of selected reaction monitoring. The chromatographic run-time for one injection was less than 6 min. Th e intra-and inter-assay coefficients of variation for the lowest conce ntration examined (30 pg ml(-1)) were 9.83 and 10.67, respectively. An d the analytical recovery of OCT added to serum was quantitative. Assa y linearity was obtained in the range of 20-640 pg ml(-1). (C) 1998 El sevier Science B.V.