Low-energy collision-induced dissociation of B1-type sugar ions formed from peracetylated methyl pentosides and methyl 6-deoxyhexosides

Abstract

Low-energy collision-induced dissociation (CID) was explored for the purpose of differentiating between isomeric pertrideuteroacetylated aldopentosides, 6-deoxyaldohexosides and their respective furanosidic and pyranosidic analogues. The 1-O-methylated derivatives were analyzed by gas chromatography/chemical ionization (CH4) tandem mass spectrometry. B1 ions (formally C(1) carbenium ions), which are expected to reflect the core structure of the parent sugar and which were produced by the elimination of methanol from the protonated glycoside derivatives, were used as precursor ions to obtain the corresponding CID spectra. In general, strong similarities which impede an unequivocal differentiation of the individual constituents were found in the spectral patterns of the different isomeric pairs. However, examination of the pseudo-breakdown behavior of the B1 ions over the range 5–35 eV revealed improved distinction windows which provide for a fuller differentiating capability between five-and six-membered ring isomers including even the most problematic ribose derivatives. The reliability of the analyses is enhanced by the high reproducibility (s<10%) of these ratios. The considerable similarity between the tandem mass spectra of certain furanosidic and pyranosidic B1 ions is highly suggestive of a partial loss of structural integrity, mainly due to ring contraction, which occurs to different extents in the different isomers. Copyright © 1999 John Wiley & Sons, Ltd.