Characteristics of mass spectrometric analyses coupled to gas chromatography and liquid chromatography for 22-oxacalcitriol, a vitamin D3 analog, and related compounds

The characteristics of the mass spectra of vitamin D-3 related compounds were investigated by GC-MS and LC-MS using 22-oxacalcitriol (OCT), an analog of 1,25-dihydroxyvitamin D-3, and related compounds. Fragmentation during GC-MS (electron impact ionization) of TMS-derivatives of OCT and the postulated metabolites gave useful structural information concerning the vitamin D-3-skeleton and its side-chain, especially with respect to the oxidation positions of metabolites. In contrast, few fragment ions were observed in LC-MS (atmospheric pressure chemical ionization), showing that LC-MS gave poor structural information, except for molecular mass. However, when comparing the signal-to-noise ratio (S/N) observed during GC-MS and LC-MS analysis for OCT in plasma extracts, the S/N in LC-MS was over ten-times greater than in GC-MS, possibly due to the low recovery on derivatization and thermal-isomerization in GC-MS. Furthermore, both the GC-MS and the LC-MS allowed the analysis of many postulated metabolites in a single injection without any prior isolation of target metabolites from biological fluids by LC. These results suggest that GC-MS and LC-MS analysis for vitamin D-3 related compounds such as OCT each have unique and distinct advantages. Therefore, the complementary use of both techniques enables the rapid and detailed characterization of vitamin D-3 related compounds. (C) 1997 Elsevier Science B.V.