A highly sensitive and specific gas chromatographic/mass spectrometric method was developed for the determination of very low levels of F6-1,25(OH)2 vitamin D3, a new fluoro analogue of vitamin D3, to facilitate investigation of its pharmacokinetics in man. Deuterium-labelled F6-1,25(OH)2 vitamin D3 was employed as an internal standard for quantification. The method involves extraction from serum samples, separation by a cartridge column system followed by straight-phase high-performance liquid chromatography, O-trimethylsilylation, and analysis by gas chromatography/mass spectrometry using high-resolution selected ion monitoring. With a quantification limit of 2 pg ml-1 and a requirement for 2 ml of serum, the assay method has sufficient sensitivity, selectivity and precision for the analysis of very low concentrations of the drug.
Calcitriol Chromatography, High Pressure Liquid