Profile and Flight Time Analysis of Bovine Insulin Clusters as a Probe of Matrix-assisted Laser Desorption/Ionization Ion Formation Dynamics

Detailed ion signal profile and flight time analyses were performed on the time-of-flight signals obtained for bovine insulin cluster ions produced by matrix-assisted laser desorption/ionization (MALDI). Profile analyses of the ion signals strongly suggest that the signals are made up of a composite of two separate components and analysis of the flight times of the two components suggests that the ions are formed with different dynamics. The formation dynamics of one component of the ions is best described as prompt ionization to yield ions with essentially mass-independent total energies. The formation dynamics of the second component of the ions is best described as delayed gas-phase ionization of entrained material moving at a constant velocity. This model is supported by several ancillary experiments and suggests new insights into the mechanism of MALDI ion formation.