Structural characterization of hexoses and pentoses using lead cationization. An electrospray ionization and tandem mass spectrometric study

The analytical potential of the complexation of isomeric underivatized hexoses ( D ‐glucose, D ‐galactose, D ‐mannose, D ‐talose, D ‐fructose), methylglycosides (1‐ O ‐methyl‐α‐ D ‐glucose and 1‐ O ‐methyl‐β‐ D ‐glucose) and pentoses ( D ‐ribose, D ‐xylose, D ‐arabinose and D ‐lyxose) by Pb 2+ ions, was investigated by electrospray ionization and tandem mass spectrometry (MS/MS). Pb 2+ ions react mainly with monosaccharides by proton abstraction to generate [Pb(monosaccharide) m − H] + ions ( m = 1–3). At low cone voltage, a less abundant series of doubly charged ions of general formula [Pb(monosaccharide) n ] 2+ is also observed. The maximum number n of monosaccharides surrounding a single Pb 2+ ion depends on the metal : monosaccharide ratio. Our study shows that MS/MS experiments have to be performed to differentiate Pb 2+ ‐coordinated monosaccharides. Upon collision, [Pb(monosaccharide) − H] + species mainly dissociate according to cross‐ring cleavages, leading to the elimination of C n H 2 n O n neutrals. The various fragmentation processes observed allow the C(1), C(2) and C(4) stereocenters of aldohexoses to be characterized, and also a clear distinction aldoses and fructose. Furthermore, careful analysis of tandem mass spectra also leads to successful aldopentose distinction. Lead cationization combined with MS/MS therefore appears particularly useful to identify underivatized monosaccharides. Copyright © 2002 John Wiley & Sons, Ltd.