Ionization and collision-induced fragmentation of N-linked and related carbohydrates using divalent canons

Maltoheptaose and several N-linked glycans were ionized by electros pray as adducts with the divalent canons Mg2+, Ca2+, Mn2+, Co2+ and Cu2+. [M + metal](2+) ions were the major species in all cases with calcium giving the highest sensitivity. In addition, copper gave [M + Cu](+) ions. Other canons gave singly charged ions only by elimination of a protonated monosaccharide. Fragmentation of the [M + metal](2+) ions produced both singly and doubly charged ions with the relative abundance of doubly charged ions decreasing in the order Ca > Mg > Mn > Co > Cu. Singly charged ions were formed by elimination of a protonated monosaccharide residue followed, either by successive monosaccharide residue losses, or by a (2,4)A cross-ring cleavage of the reducing-terminal monosaccharide. Formation of doubly charged fragments from [M + metal](2+) ions involved successive monosaccharide-residue losses either with or without (O,2)A or (2,4)A cross-ring cleavages of the reducing-terminal monosaccharide. Abundant diagnostic doubly charged ions formed by loss of the 3-antenna from the (O,2)A cross-ring product were specific to (M + Ca]2+ ions. Fragmentation of (M + Cu](+) ions was similar to that of the corresponding [M + H](+) ions in that most cross-ring fragments were absent. (C) 2001 American Society for Mass Spectrometry.