Ion Guide for Improved Atmosphere to Mass Spectrometer Vacuum Ion Transfer

Abstract

Various approaches for transmitting ions from atmosphere to the deep vacuum required for mass analysis have been developed with the goal to increase the ion to gas ratio while maintaining high ion transmission efficiency. Since the vast majority of ion losses occurs in the atmospheric pressure ion source, an effective way to improve sampling of those ions is to increase the atmosphere to vacuum aperture diameter. However, as the aperture diameter is increased, the resulting intense free jet gas expansion and subsequent gas beam can scatter ions in the first vacuum region. The interface described here provides an optimized flow field to the second vacuum stage, with a unique geometry to counter the ion losses from scattering collisions with the gas. Two additional differentially pumped quadrupole ion guides are used to further improve the ion to gas ratio, resulting in an ion transfer efficiency improvement of 5-6× over a two-stage differentially pumped interface with quadrupole ion guides. The interface also demonstrates efficient declustering and fragmentation capabilities beneficial for reducing background chemical noise.