SPIN-COATED SAMPLES FOR HIGH-RESOLUTION MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY OF LARGE PROTEINS

The preparation of near homogeneous samples of large biomolecules, bas ed on the method of spin coating sample substrates, and their use in m atrix-assisted laser/desorption ionization mass spectrometry, for gene rating spectra with highly reproducible ion signals of analyte molecul es with mass extending up to about 150 000 u, are reported. These samp les, which could easily be reproduced, consisted of a uniform distribu tion of matrix/analyte microcrystals over the entire sample surface. U pon laser irradiation, they provided enhanced molecular ion yields and thereby allowed the acquisition of good quality mass spectra over a f ew (similar to 1-5) laser pulses. Methods for improving the mass resol ution of the molecular ion signals were examined, and a spectrum of bo vine insulin obtained from a linear time-of-flight instrument with a m ass resolution in excess of 1450, together with one of chicken egg lys ozyme displaying a resolution of about 450, are presented. The influen ce of the matrix/analyte molar ratio on the molecular ion yield has al so been studied.