Kinetic energy measurements of molecular ions ejected into an electric field by matrix-assisted laser desorption

Measurements of kinetic energy distributions of molecular ions ejected into an extraction field by matrix‐assisted laser desorpton re reported. The measurements were made in a time‐of‐flight mass spectrmeter with an electrostatic mirror by measuring the reflected signal as a function of the difference between the accelerating voltage and the voltage applied t the mirror. The molecular ions ere found to have less kinetic energy than the extraction field alone would normally provide, i.e. we observed an nergy deficit. Under conditons typical for a matrix‐assisted laser desrptio experiment, the deficit is about 24 eV for oleclar ions of insulin. The size of the deficit increases with the intensity of the molecular ion signal, and the molecular weight of the protein; t is also larger for negative molecular ions than for positive molecular ions.