PNNL

Abstract

Invented in the 1990s, the ion funnel enabled a new approach for transporting ions through the first vacuum stage of a mass spectrometer, providing much greater transmission efficiencies than other techniques at the time. Rather than use a conical skimmer to sample a small portion of the ions entering the vacuum chamber from the inlet of an electrospray ionization interface, the ion funnel was designed to capture all of the ions in the expanding gas jet and radially focus them for efficient transfer through a conductance limiting orifice at pressures where traditional ion guiding devices failed. While initial designs required high speed pumping and exhibited a strong mass to charge ratio (m/z)-dependent ion transmission bias, subsequent advances guided by theoretical modeling have overcome those limitations to provide consistently large sensitivity gains and robust operation for a wide variety of mass spectrometers. We review the improvements in design and understanding that have brought the ion funnel to its current state of refinement. Novel applications of the ion funnel, which are continually emerging in such diverse fields as ion trapping, ion cooling, low pressure electrospray, and ion mobility spectrometry, are reviewed as well.