USE OF A CONVENTIONAL POINT DETECTOR TO RECORD MATRIX-ASSISTED-LASER-DESORPTION IONIZATION SPECTRA FROM A MAGNETIC-SECTOR INSTRUMENT/

Matrix-assisted laser desorption/ionization mass spectra were recorded on a magnetic sector mass spectrometer using the point detector by us ing the laser pulses to outline the ion peaks. The instrument was set to scan slowly so that about 10 laser shots were fired during the time the instrument took to scan over a mass peak This procedure produced a succession of signals that defined the ion peak profile. The profile was then obtained by smoothing the data. Although slow, this techniqu e enables the mass spectrum to be obtained in a single scan and also e nables high resolution data to be acquired; the spectrum of the biante nnary N-linked gly can [(Gal)(2)(Man)(3)(GlcNAc)(4)] was recorded at a resolution of 15 000, The liquid binary matrix of 3-aminoquinoline an d alpha-cyano-4-hydroxycinnamic acid, introduced by Colli and Orlando, was initially used but was found to produce Schiff base derivatives w ith glycans possessing a free reducing terminus. Other binary mixtures giving prolonged ion beams were investigated and a mixture of 2,5-dih ydroxybenzoic acid and 2,4,6-trihydroxyacetophenone found to be reason ably satisfactory although less so than 3-aminoquinoline and alpha-cya no-4-hydroxycinnamic acid. Spectra were normally recorded as single sc ans from about 100 pmol of sample loaded. For low concentrations, in t he range of 1-10 pmol, spectra were averaged to produce better signal: noise ratios. The method was used to record the spectra of N-linked gl ycans released from glycoproteins. (C) 1998 John Wiley & Sons, Ltd.