Performance optimization of an ion funnel driven by novel radiofrequency waveforms.

Abstract

In mass spectrometry, ion transmission is usually achieved by driving an ion funnel with a reversed sine wave radiofrequency. However, the mass range of this conventional ion funnel is limited. In order to overcome this limitation, and to improve the transmission efficiency of the ion funnel, we explore the use of different radiofrequency waveforms for different m/z ranges. Right triangle, sawtooth, and variable phase sine (VPS) waves are used in different m/z ranges to improve ion transmission efficiency. We use SIMION-based numerics to simulate their potential field distributions and ion flight trajectories. We compare transmission and focusing performances with those of a conventional ion funnel. Ions with high m/z values require a larger potential gradient to limit their flight trajectory. Right triangle waves can quickly adjust electrode potential through a step change. The equipotential line distribution of VPS waves is wider than that of a sine wave which improves focusing performance. At the same time, the local ion trap effect at the outlet of the ion funnel is improved because of the "snake potential". The maximum effective potential of the sawtooth wave is smaller than that of the sine wave, which is suitable for low m/z ion transmission. Sawtooth and VPS waves may improve the transmission performance of the ion funnel in the low m/z regime whereas right triangle waves may improve the transmission performance in the high m/z regime.