Ionisation and fragmentation of complex glycans with a quadrupole time-of-flight mass spectrometer fitted with a matrix-assisted laser desorption/ionisation ion source

This paper reports the use of an experimental matrix-assisted laser desorpt ion/ionisation (MALDI) ion source fitted to a quadrupole time-of-flight (Q- Tof) mass spectrometer for the analysis of carbohydrates, particularly the N-linked glycans from glycoproteins, Earlier work on the Q-Tof instrument, using electrospray ionisation, gave excellent MS/MS spectra, particularly f rom the [M + Na](+) ions, but suffered from the major disadvantages that th e signal was often split between singly and multiply charged ions and that sensitivity fell dramatically as the molecular weight of the carbohydrate r ose. The MALDI ion source did not suffer from these problems and the instru ment produced excellent MS and MS/MS spectra from small amounts of complex, underivatised glycans as well as those derivatised at the reducing terminu s. Positive ion MS spectra of sialylated glycans recorded on the new instru ment were much less complex than those recorded with a conventional MALDI-T OF instrument because of the absence of ions resulting from metastable (pos t-source decay, (PSD)) fragmentations occurring in the flight tube, However , considerable fragmentation by loss of sialic acid still occurred. MS/MS s pectra of the [M + Na](+) ions from all compounds were almost identical to those recorded earlier with the electrospray-Q-Tof combination and far supe rior to MALDI-PSD) spectra recorded with reflectron-TOF instruments, Spectr a are shown for neutral and sialylated N-linked glycans from chicken ovalbu min, riboflavin binding protein, alpha1-acid glycoprotein, bovine fetuin an d ribonuclease B, both as free glycans and as those derivatised at their re ducing termini, The technique was applied to the structural determination o f N-linked glycans from human secretory IgA and Apo-B 100 from:human low-de nsity lipoprotein, Copyright (C) 2000 John Wiley & Sons, Ltd.