Direct comparison of matrix-assisted laser desorption/ionisation and electrospray ionisation in the analysis of gangliosides by Fourier transform mass spectrometry

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Abstract
Both electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) coupled to a Fourier transform mass spectrometer (FTMS) are used to analyze gangliosides, providing a direct comparison of the two techniques using the same mass analyzer. Both MALDI/FTMS and ESI/FTMS gave better results in the negative ion mode. ESI/FTMS appears to be more gentle, with the majority of the ion staying intact. MALDI/FTMS leads to significantly more fragmentation. These results can be explained in terms of differences in internal energy caused by the ionization process and differences in translational energies acquired from the source, by analysis of the different trapping regimes needed in each technique. Positive ion mode ESI/FTMS gave very poor results with almost exclusive fragmentation to the asialoganglioside. Positive ion MALDI/FTMS gave good signal, but multiple metal coordination sometimes resulted. Fragmentation in ESI can be manipulated through the use of skimmer voltage differences and in MALDI through the use of alkali metal doping and laser intensity.

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