Ion spray liquid chromatographic/mass spectrometric characterization of bile acids

The ion spray mass spectra of selected bile acid standards are presented. Full-scan positive ion spectra obtained in solutions of acetonitrile-water-trifluoroacetic acid and methanol-water-trifluoroacetic acid show the presence of intense [M + S + H]+ and [M + 2S + H]+ ions (where S is either methanol or acetonitrile, depending on the solvent system) in addition to [M + H]+ ions. The relative abundance of the protonated and solvent adduct ions are reproducible and unique for several of the bile acids, and provide a means of identifying isomeric bile salts. Adduct ions are most abundant for free acids and weaker for glycine and taurine conjugates. On-line ion spray liquid chromatography/mass spectrometry (LC/MS) using a 3 cm x 4.6 mm cartridge column containing 3 microns particle size C18 packing was utilized for the separation and identification of components of monkey bile. Eight common bile acid conjugates were separated in less than 8 min utilizing a water-acetonitrile gradient with 0.1% trifluoroacetic acid as the mobile-phase modifier. Full-scan data were acquired from 1 microliter of untreated bile injected on-column. Identification of component bile acids from the equivalent of 1 nl injected on-column was obtained with the use of a 1 mm diameter microbore column. Limits of detection for bile acid conjugates using a microbore column and selected ion monitoring (SIM) range from 40 to 100 fmol.