Plume particle energy analysis of an ionic liquid electrospray ion source with high emission density

Abstract

A retarding potential analyzer was used to characterize the energy distribution of the plume particles from an electrospray source. The electrospray device uses an ionic liquid, operates at bipolar and relatively high voltages from ± 1800 to ± 3500 V, and demonstrated ionic emissions with a relatively high emission density of more than ± 30 μ A per emission tip. Electrostatic simulations were used to study the effects of electric field distortion near the grids in the retarding potential analyzer, and a correction factor of 93% was used to regulate the deceleration voltage in the energy analysis, from which the voltage losses between the applied voltage of the electrospray source and the actual acceleration voltage of the charged particles were calculated, demonstrating non-kinetic efficiency from 85.8% at - 2100 V to 79.6% at 2600 V. The plume particle energy analysis shows evidence of fragmentation of heavier particles, mostly from dimer ions to monomer ions, and the detailed energy analysis was used to estimate the position where the fragmentation occurs. The results suggest that about 45%-55% of the particle fragmentation occurred in the field-free region and 20%-30% occurred in the acceleration region with an intense electric field, with the rest of the plume containing unfragmented ions.