Characterization of acyl-linked glucuronides by electron impact and fast atom bombardment mass spectrometry.

Thirty-one electron impact (EI) mass spectra and 22 fast atom bombardment (FAB) mass spectra were evaluated with regard to providing molecular weights and information about the structures of 1-O-acyl glucuronides. Molecular ion species were obtained by both techniques. Fragmentation of the glycosidic and carboxylate bonds produced ions characteristic of glucuronides as a class, and also ions unique to acyl glucuronides. In EI mass spectra of pertrimethylsilylated derivatives, pairs of [M - 481]+ and [M - 509]+ ions characterized the acyl linkage. Relative abundances within these pairs correlated with the benzylic, benzoic or aliphatic nature of the carboxylate group. Positive ion FAB spectra contained three sets of ions, with intervals of 28 and 46 mass units, which characterized the linkage. In negative ion FAB spectra, a characteristic pair of fragment ions 44 mass units apart were accompanied by anions of mass 193, which appeared to distinguish acyl from phenol and hydroxyl glucuronides.