DIRECT SPECIES-SELECTIVE DETERMINATION OF COBALAMINS BY IONSPRAY MASS-SPECTROMETRY AND IONSPRAY TANDEM MASS-SPECTROMETRY

A direct method for the simultaneous compound-specific determination o f vitamin B-12 (cyanocobalamin), its analogues methylcobalamin, hydrox ocobalamin, adenosylcobalamin (coenzyme B-12) and cobinamides by ionsp ray MS was developed, Single and tandem MS modes mere compared, For al l the compounds except hydroxocobalamin, the most intense ion formatio n was observed as a result of protonation of the original molecular ca tion leading to an analytically useful doubly charged ion, For hydroxo cobalamin a similar process leads to the loss of the functional group leading to the [Cbl + H](2+) ion, which is analytically useful only in the absence of other cobalamins, Hydroxocobalamin can be determined i n the presence of other compounds using the minor [OH-Cbl](+) ion, The calibration curves are linear in the range 0.01-1 mu g ml(-1), which can be extended up to 10 mu g ml(-1) if alternative ions are chosen, D etection limits of 5-40 ng ml(-1) are obtained, Collision-induced diss ociation leads first to the loss of the Co substituent (Me, CN, OH, ad enosyl) and thus to a decrease in selectivity, The method was applied to the analysis of a synthetic mixture of the cobalamins and to the de termination of hydroxocobalamin in a commercial pharmaceutical prepara tion.