Effect of structure on the signal strength of oligosaccharides in matrix-assisted laser desorption/ionization mass spectrometry on time-of-flight and magnetic sector instruments.

The signal strength of the MNa+ ion from 25 underivatized oligosaccharides (linear, and both O- and N-linked oligosaccharides from glycoproteins) was measured by matrix-assisted laser desorption/ionization mass spectrometry on a time-of-flight and on a magnetic sector instrument with 2,5-dihydroxybenzoic acid as the matrix, in order to examine the influence of structure on ion abundance. Oligosaccharides with masses greater than about 1000 Da exhibited similar signal strengths, irrespective of structure, when examined on the time-of-flight instrument. Oligosaccharides with masses below 1000 Da displayed a progressive reduction in signal intensity with decreasing molecular weight, an effect which was probably due to temporary saturation of the detector by the intense matrix ions (m/z 130-200 region). Similar studies performed on a magnetic sector instrument revealed that all oligosaccharides studied produced signals of equivalent intensity and that no reduction in signal strength occurred with the smaller sugars. The compounds could be measured with a precision of +/- 5% on this instrument. The nature of the matrix did not appear to exert a differential effect on the ionization of sugars of different structural types although some matrices appeared to have a preference for ionization of smaller molecules.