Nonlinear ion acceleration for improved space focusing in time-of-flight mass spectrometry

AbstractThe initial spatial distribution of gas-phase ions is one of the primary factors limiting the achievable mass resolving power in time-of-flight mass spectrometry. While the effect of the spatial distribution is minimized along the flight path at a location known as the space-focus plane, the use of a single, linear acceleration field to generate this focus represents only a first-order approximation of ideal space focusing. Alternatively, ideal space focusing is possible through the use of a nonlinear ion acceleration field. A computational model delineates the requirements of the nonlinear potential profile, and suggests that substantial improvements to resolving power can be achieved when using an ion source configuration where a first field approximates the optimal nonlinear field gradient and a second, linear accelerating field imparts additional kinetic energy. Experimental results using a novel, static-field ion source geometry designed to allow selective position-specific ionization through photoinduced dissociation indicate that a 10× improvement in focusing can be achieved using this configuration