APPLICATION OF MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY WITH DELAYED ION EXTRACTION TO GANGLIOSIDE ANALYSES

Various monosialo- and disialo-gangliosides and their derivatives were examined by delayed ion extraction matrix-assisted laser desorption i onization time-of-flight mass spectrometry (DE MALDI-TOF MS) in the re flector mode with alpha-cyano-4-hydroxycinnamic acid or 2,5-dihydroxyb enzoic acid used as the matrix, Native gangliosides were generally fou nd to give good spectra in the negative ion mode, 2,5-Dihydroxybenzoic acid was a better matrix for gangliosides than alpha-cyano-4-hydroxyc innamic acid, because this matrix seemed to minimize loss of sialic ac id and carbon dioxide of gangliosides. About 1 pmol of ganglioside was able to be detected with this matrix, when ''A-series'' gangliosides such as GD1a and GalNAc-GD1a gave undesirable extra peaks probably due to loss of sialic acid besides molecule-related ion peaks, the methyl -esterification of the gangliosides at the carboxyl groups of sialic a cids was found to be necessary to obtain good DE MALDI-TOF mass spectr a in the positive ion mode, In contrast, ''B-series'' gangliosides suc h as GD1b, GD2, and GD3 gave rise to major dehydrated molecule-related ion [M-H2O-H](-) peaks in the negative ion mode without the pretreatm ent of methyl-esterification. The DE MALDI-TOF mass spectrometric anal ysis enabled us to distinguish between GD1a and GD1b, which have the s ame molecular weight, It was also found that not only a purified sampl e, but also a mixed sample of various gangliosides was amenable to the identification of them by DE MALDI-TOF MS.