Factors affecting the resolution in matrix-assisted laser desorption—ionization mass spectrometry

Abstract The influence of the physical parameters laser spot size, laser irradiance and angle of incidence on the mass resolution of matrix-assisted UV-laser desorption—ionization spectra has been investigated for a reflector-type time-of-flight (TOF) mass spectrometer. Minimal peak widths 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 μm in diameter, at the lowest laser irradiance for ion generation, and in the mass range below about 2000 Da. Mass resolutions of up to m /δ m = 5000 (FWHM) have been obtained for peptides up to about 3000 Da. The reduction of mass resolution observable under non-optimized experimental conditions can be rationalized by the increasing amount of material ablated, enhanced number of collisions in the desorbed plume, and by an increase of the effective ionization time. At larger masses the non-resolved isotopic distributions also contributes to teh decline in the mass resolution.