Thermospray liquid chromatography/tandem mass spectrometry of thermally labile xenobiotic conjugates

Abstract

A strategy for thermospray liquid chromatography/tandem mass spectrometry (TSP LC/MS/MS) of very thermally labile xenobiotic conjugates, such as acetaminophen (AA) conjugates, selected as model compounds in biological fluid, was examined. The vaporizer temperature as well as collision energy were optimized using authentic AA-glutathione conjugate without modification of any analytical conditions, including mobile-phase composition, ion source temperature and repeller voltage. The [MH]+ ion intensities in the parent ion mass spectrum of m/z 182 from the conjugate at a collision energy of -25 eV were improved and maximized with a lowering of the vaporizer temperature from 115°C, corresponding to the optimal vaporization temperature of the mobile phase, to 80°C. Bile obtained from rats was treated with an equimolar mixture of AA and (2H3)AA was directly injected into the TSP LC/MS/MS system to perform the metabolic mapping of AA. The glucuronic acid, sulphuric acid, glutathione and cysteinylglycine conjugates of AA, in addition to the parent drug, were detectable by the parent ion scan mode, and confirmation of each structure could be obtained by the daughter ion scan mode. These conjugates appeared to show a marked temperature effect on the quality of TSP tandem mass spectra and sensitivity.