Ion Bunching in Square-Wave-Driven Mobility Capillary Electrophoresis-Mass Spectrometry

The ion-bunching effect was typically produced for ion beams in the gas phase, such as in ion accelerators. In this work, ion bunching was generated for ions in a liquid channel, specifically in a mobility capillary electrophoresis-mass spectrometry (MCE-MS) setup. MCE was recently developed and coupled with MS for ion separation and the precise measurements of ion hydrodynamic radius and effective charge in solution. In conventional MCE, a DC high voltage is applied, which serves as the separation voltage. In this study, square waves were employed to replace this DC voltage, and the ion-bunching phenomenon was observed and characterized in both simulations and experiments. After applying a high voltage square wave, cations and anions would be bunched and concentrated at the positive and negative half cycle of the square wave, respectively. Accordingly, ion signal intensities detected by the following mass spectrometer could be increased by up to similar to 50 folds for the aspartic acid anion. This square wave could also dissociate metal adduct cations from nucleic acid anions, which results in stronger nucleic acid ion intensities (up to similar to 10 folds) with cleaner backgrounds.

Automated summary

In this study, ion bunching in a liquid channel was achieved by replacing the DC voltage with square waves. The ions were concentrated and grouped in the positive and negative half cycles of the square wave, leading to increased ion signal intensities. This research has great significance for ion separation and measurement.