Direct species-selective determination of cobalamins by ionspray mass spectrometry and ionspray tandem mass spectrometry

A direct method for the simultaneous compound-specific determination of vitamin B-12 (cyanocobalamin), its analogues methylcobalamin, hydroxocobalamin, adenosylcobalamin (coenzyme B-12) and cobinamides by ionspray MS was developed, Single and tandem MS modes mere compared, For all the compounds except hydroxocobalamin, the most intense ion formation was observed as a result of protonation of the original molecular cation leading to an analytically useful doubly charged ion, For hydroxocobalamin 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 in 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, Detection limits of 5-40 ng ml(-1) are obtained, Collision-induced dissociation leads first to the loss of the Co substituent (Me, CN, OH, adenosyl) and thus to a decrease in selectivity, The method was applied to the analysis of a synthetic mixture of the cobalamins and to the determination of hydroxocobalamin in a commercial pharmaceutical preparation.