Fast atom bombardment combined with tandem mass spectrometry for determination of bile salts and their conjugates.

Fast atom bombardment desorption of bile salts produces negative ions which show little fragmentation. The lack of fragmentation limits the utility of the method for resolving questions regarding specific structural features. This paper is a report of negative ion fast atom bombardment mass spectra and collision-activated decomposition spectra of cholate, chenodeoxycholate, lithocholate, taurocholate, taurochenodeoxycholate, taurolithocholate, 3 beta-ol-5-cholenate, taurolithocholate-3-sulfate and glycolithocholate-3-sulfate. The collision-activated decomposition spectra are useful for distinguishing bile salt structural features and for quantifying relative amounts of isomeric ions in a mixture. The negative ion mode is well suited for generating anions of bile salts and, when coupled with collisional activation, provides complementary information to the positive ion mode. The collision-activated fragmentation is also unusual as it appears to be an example of reactions occurring remote from the charge site. Furthermore, on the basis of the fragmentations, the charge site can be located in the amphiprotic form of some gas-phase diprotic bile acids such as taurolithocholate-3-sulfate and glycolithocholate-3-sulfate.