Positive and negative ion fast atom bombardment mass spectrometry of glycosphingolipids. Discrimination of the positional isomers of gangliosides with sialic acids.

High molecular weight gangliosides (GD1a, GD1b, GT1a, and GT1b) and neutral glycosphingolipids (Forssman antigen, globoside, and CTH) containing various fatty acids were analyzed by positive and negative ion fast atom bombardment mass spectrometry (POS-FAB-MS and NEG-FAB-MS) without any derivatization. NEG-FAB-MS of the molecules gave intense peaks of the molecular ion species, (M-H)-, and many fragment ions useful for the elucidation of carbohydrate structure were also detected with significant intensity. The fragment ions were assessed to be cleaved at the glycosidic linkages sequentially from the non-reducing end with or without the ceramide portion and it was possible to distinguish structural isomers having different binding positions of sialic acid. All molecular ion species of neutral glycosphingolipids with various fatty acids were detected at intensities that were in accordance with the relative abundance of the fatty acids.