FACTORS AFFECTING THE RESOLUTION IN MATRIX-ASSISTED LASER-DESORPTION IONIZATION MASS-SPECTROMETRY

The influence of the physical parameters laser spot size, laser irradi ance and angle of incidence on the mass resolution of matrix-assisted UV-laser desorption-ionization spectra has been investigated for a ref lector-type time-of-flight (TOF) mass spectrometer. Minimal peak width s are in the range of the laser pulse duration, i.e. a few nanoseconds . Such narrow ion signals can be obtained only for spot sizes of more than about 70 mum in diameter, at the lowest laser irradiance for ion generation, and in the mass range below about 2000 Da. Mass resolution s of up to m/deltam = 6000 (FWHM) have been obtained for peptides up t o about 3000 Da. The reduction of mass resolution observable under non -optimized experimental conditions can be rationalized by the increasi ng amount of material ablated, enhanced number of collisions in the de sorbed plume, and by an increase of the effective ionization time. At larger masses the non-resolved isotopic distributions also contributes to the decline in mass resolution.