Determination of 22-oxacalcitriol, a new analog of 1alpha,25-dihydroxyvitamin D3, in human serum by liquid chromatography-mass spectrometry.

A sensitive and specific liquid chromatographic-mass spectrometric assay has been developed for the determination of 22-oxacalcitriol (OCT), which is a new analog of 1alpha,25-dihydroxyvitamin D3. The analyte was isolated from serum by two solid-phase extraction steps on a C18 cartridge and NH2 cartridge. The recovery of OCT through two extraction 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 standard. Extracts were chromatographed on a C18 reversed-phase column interfaced to the electrospray ionization source. The mass spectrometer was operated in the positive-ion mode of selected reaction monitoring. The chromatographic run-time for one injection was less than 6 min. The intra- and inter-assay coefficients of variation for the lowest concentration examined (30 pg ml[-1]) were 9.83 and 10.67, respectively. And the analytical recovery of OCT added to serum was quantitative. Assay linearity was obtained in the range of 20-640 pg ml(-1).