Three dissociation methods, including collision-induced dissociation (CID), electron capture dissociation (ECD), and electronic excitation dissociation (EED), were evaluated for the dissociation of doubly charged glycans using sodium or magnesium ions as charge carriers. CID produced mainly glycosidic cleavages, although more cross-ring fragment ions could be obtained at higher intensities when magnesium ions were used as charge carriers [M + Mg]²⁺. The ^0,2A₃, ^0,3A₃, and ^0,4A₃ ions provided structural information on the 3 → 1 and 6 → 1 linkages of the mannoses. Some internal fragment ions, such as ^2,4A₅_Y_3β, were also produced in high abundance, thus providing additional information on the glycan structure. ECD produced limited fragments compared to other dissociation methods when either of the metal ions were used as charge carriers. Cross-ring fragments were obtained in relatively high abundance, with the charge mainly retained on the nonreducing end. EED produced extensive glycosidic and cross-ring cleavages when either metal charge carrier was used. A higher fragmentation efficiency was achieved and more structural-specific fragments were produced when Na⁺ was used as the charge carrier. Of the 31 possible cross-ring cleavages, including 0,2-, 0,4-, 1,5-, 2,4-, and 3,5-cleavages, 25 were found, thus providing extensive linkage information. A wide range of fragment ions could be obtained in all dissociation methods when Mg²⁺ was used as the charge carrier. Two specific analytical approaches were found to produce extensively structural-specific information on the glycans studied, namely CID of magnesiated glycans and EED of sodiated glycans. These two methods were selected to further analyze the larger mannose-rich glycans Man₆GlcNAc₂ and Man₈GlcNAc₂ and generated extensive structural information.

H.-T. Kitty Wong

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