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, based on the method of spin coating sample substrates, and their use in matrix-assisted laser/desorption ionization mass spectrometry, for generating spectra with highly reproducible ion signals of analyte molecules with mass extending up to about 150 000 u, are reported. These samples, which could easily be reproduced, consisted of a uniform distribution of matrix/analyte microcrystals over the entire sample surface. Upon laser irradiation, they provided enhanced molecular ion yields and thereby allowed the acquisition of good quality mass spectra over a few (similar to 1-5) laser pulses. Methods for improving the mass resolution of the molecular ion signals were examined, and a spectrum of bovine insulin obtained from a linear time-of-flight instrument with a mass resolution in excess of 1450, together with one of chicken egg lysozyme displaying a resolution of about 450, are presented. The influence of the matrix/analyte molar ratio on the molecular ion yield has also been studied.