Comparative Study of Acidic Glycosphingolipids by Field Desorption and Secondary Ion Mass Spectrometry1

Abstract

Acidic glycosphingolipids were analyzed by field desorption (FD-MS) and secondary ion mass spectrometry (SI-MS) using the primary ion Xe⁺ with a glycerol matrix. In the analysis of underivatized gangliosides by FD-MS, the fragment corresponding to the asialo residue resulting from the cationized cluster ion (M+Na)⁺ was the base peak, and ions due to cleavage at the glycosidic linkages were detected, as in the neutral glycosphingolipids. In the case of sulfatide, the ceramide fragment showed the highest intensity in the spectrum. In SI-MS spectra of acidic glycosphingolipids, (M+Na)⁺, (M+2Na-H)⁺, and (M+K)⁺ were continuously detected as relatively high intensity ions during analysis of gangliosides and sulfatide. Other ions were mostly similar to those obtained by FD-MS. In FD-MS spectra of permethylated gangliosides, the cationized molecular ion (M+Na)⁺ was the base peak, and fragment ions due to asialo gangliosides were prominent. Other peaks were hard to detect. In SI-MS, molecular ions (M+H)⁺ and (M+H-32)⁺ and other ions due to cleavage of the glycosidic linkages were clearly detected. In this case, the sensitivity was greatly improved. Ions due to the non reducing end sugars were clearly detected, because of the relatively low intensity of ion peaks due to the glycerol matrix. It is concluded that the combination with FD-MS and SI-MS is particularly useful for the determination of molecular weight, sugar sequence and ceramide structure with sample amounting to only a few μg order.