False sugar sequence ions in electrospray tandem mass spectrometry of underivatized sialyl-Lewis-type oligosaccharides

Formation of ''false'' sugar sequence ions from branched tetrasaccharides of the sialyl-Lewis-type by migration of fucose towards sialic acid residues is shown to occur in [M + H](+) and [M + NH4](+) ions produced by electrospray ionization and subjected to low energy collision induced dissociation (CID). For the verification of their composition and sequence, such irregular ions were produced in the orifice region of the ion source, mass selected in Q1, and subjected to a second CID step in Q2 of a triple quadrupole analyser. When produced and analysed in the same ''double CID'' fashion, the branched Bg ions Still containing all four sugar subunits show such migration to only a minor extent. The analysis of B-n fragment ions with high numbers for n may thus have advantages over the analysis of M-like species. (C) 1997 Elsevier Science B.V.