Space charge compensation in air by counterion flow in 3D printed electrode structure

Abstract

Electrospray ionization is commonly employed in modern mass spectrometry experiments for applications ranging from proteomics to environmental science and for fundamental studies of the chemical reactivity of ions. Despite the ubiquity of electrospray ionization, the total ion currents achieved using the technique remain relatively poor. While there are significant losses within the atmospheric pressure interface of the mass spectrometer (MS), many ions are lost due to space charge repulsion before ions and charged microdroplets enter the instrument. Space charge effects also limit the extent to which multiplexing of electrosprays can be used to increase ion currents. In this work, a flow of oppositely charged ions produced by atmospheric pressure chemical ionization (APCI) is employed to mitigate space charge effects in an analyte ion beam produced by nanoelectrospray ionization (nESI) as it is passed through an atmospheric pressure ion guide outside of a mass spectrometer. A decrease in the nESI beam width together with an increase in peak intensity is observed using an ion charge coupled detector in the presence of a counterflow of ions of the opposite charge. This result indicates that focusing occurs in the ion guide. Measurements of the space charge compensated ion beam using an Agilent Ultivo triple quadrupole mass spectrometer are correlated with changes in ion focusing, indicating that space charge compensation occurring before the ion beam enters the mass spectrometer can increase detected ion currents.