Structural characterization of monosialo-, disialo- and trisialo-gangliosides by negative ion AP-MALDI-QIT-TOF mass spectrometry with MS(n) switching.

The atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) is a quite convenient soft ionization for biomolecules, keeping analytes atmospheric conditions instead of high vacuum conditions. In this study, an AP-MALDI ion source has been coupled to a quadrupole ion trap time-of-flight (QIT-TOF) mass spectrometer, which is able to perform MS(n) analysis. We applied this system to the structural characterization of monosialogangliosides, GM1 (NeuAc) and GM2 (NeuAc), disialogangliosides, GD2 (NeuAc, NeuAc), GD1a (NeuAc, NeuAc) and GD1b (NeuAc, NeuAc) and trisialoganglioside GT1a (NeuAc, NeuAc, NeuAc). In this system, the negative ion mass spectra of MS, MS(2) and MS(3), a set of three mass spectra, were able to measure within 2 s per cycle. Thus, obtained results demonstrate that the negative ion mode MS, MS(2) and MS(3) spectra provided sufficient information for the determination of molecular weights, oligosaccharide sequences and ceramide structures, and indicate that the AP-MALDI-QIT-TOF mass spectrometry keeping analytes atmospheric conditions with MS(n) switching is quite useful and convenient for structural analyses of various types of sialic acid-containing GSLs, gangliosides.