Nomenclature of Fragment Ions

The accepted nomenclature for naming fragment ions from carbohydrates is that introduced by Domon and Costello in 1988 [261] (Figure 3.6). Ions that retain the charge at the reducing terminus are designated X (cross ring), Y, and Z (glycosidic), whereas ions with the charge at the nonreducing terminus are A (cross ring), B, and C (glycosidic). Sugar rings are numbered from the nonreducing end for A, B, and C ions and from the reducing end for the others. Ions are designated by a subscript number that follows the letter to show the bond that is broken. However, for discussion purposes, in order to avoid the A, B, and C subscripts changing for glycans that have different length chains, we have introduced a modification in which the subscript numbers have been replaced by the subscript R (for reducing-terminal GlcNAc), R-1 (penultimate GlcNAc), and so on. [262]. Fragments from branched-chain glycans are distinguished by Greek letters following the subscript, with a representing the largest chain. The bonds that are broken in cross-ring cleavages are shown by superscripts preceding the letter.

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