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 ionization time-of-flight mass spectrometry (DE MALDI-TOF MS) in the reflector mode with alpha-cyano-4-hydroxycinnamic acid or 2,5-dihydroxybenzoic acid used as the matrix, Native gangliosides were generally found to give good spectra in the negative ion mode, 2,5-Dihydroxybenzoic acid was a better matrix for gangliosides than alpha-cyano-4-hydroxycinnamic acid, because this matrix seemed to minimize loss of sialic acid 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 acids was found to be necessary to obtain good DE MALDI-TOF mass spectra in the positive ion mode, In contrast, ''B-series'' gangliosides such as GD1b, GD2, and GD3 gave rise to major dehydrated molecule-related ion [M-H2O-H](-) peaks in the negative ion mode without the pretreatment of methyl-esterification. The DE MALDI-TOF mass spectrometric analysis enabled us to distinguish between GD1a and GD1b, which have the same molecular weight, It was also found that not only a purified sample, but also a mixed sample of various gangliosides was amenable to the identification of them by DE MALDI-TOF MS.