Infrared matrix-assisted laser desorption/ionization mass spectrometry for quantification of glycosaminoglycans and gangliosides

Infrared matrix-assisted laser desorption/ionization (IR-MALDI) is a "softer" ionization technique than UV-MALDI. In the present study, IR-MALDI using a 6 mu m laser produced clean negative ion mass spectra of sulfated disaccharides, from heparin and chondroitin sulfate, without significant loss of sulfate groups. The sulfur content (wt%) of chondroitin sulfate could be calculated from the m/z and the signal intensity of di- and tetra-saccharides derived from chondroitinase digestion. Similarly, no significant loss of sialic acid occurred in poly-sialylated gangliosides including GD1b, GT1b and GQ1b. Interestingly, multiply deprotonated [M-nH](n-) ions were observed in their mass spectra, and were useful for relative quantification of gangliosides in complex mixtures. These features of IR-MALDI were anticipated to be useful for robust discrimination and quantification of different gangliosides by a mass imaging technique. The multiply deprotonated ions observed in the 6 mu m laser IR-MALDI mass spectrum suggested that the mechanism underlying deprotonated ion generation might differ between the 2.94 mu m and 6 mu m laser wavelengths. (C) 2010 Elsevier B.V. All rights reserved.