POLYETHYLENE MEMBRANE AS A SAMPLE SUPPORT FOR DIRECT MATRIX-ASSISTED LASER-DESORPTION IONIZATION MASS-SPECTROMETRIC ANALYSIS OF HIGH-MASS PROTEINS

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-M S) of high mass proteins (> 100 000 Da), directly deposited on polyeth ylene membranes, is demonstrated. The spectral quality obtained, using standard sample preparation conditions, is equal or superior to that obtained with metal sample stages. Compared to the use of poly(vinylid ene difluoride) transfer membranes, this material allows the acquisiti on of excellent quality MALDI mass spectra from high-mass proteins wit h a standard UV laser. This gain in capability is not at the expense o f either mass accuracy or signal reproducibility; both approach that o btained with standard sample preparations on stainless steel. In addit ion, for the applications shown, the use of PE as a sample support red uces the severe ion suppression effects typically observed in the MALD I analysis of high-mass mixtures. This permits more precise mass measu rements to be made via the use of internal calibration and is illustra ted by the mass measurement of a chimeric mouse/human antibody (MW sim ilar to 150 000 Da) by coaddition of bovine albumin dimer (MW similar to 130 000 Da).