An Ion Funnel Interface for Improved Ion Focusing and Sensitivity Using Electrospray Ionization Mass Spectrometry

TLDR

The study develops and evaluates a novel electrohydrodynamic ion funnel interface to enhance electrospray ionization mass spectrometry sensitivity. The funnel consists of concentric ring electrodes with decreasing diameters, applying RF and DC potentials to collimate collisionally damped ions in a 1–10 Torr range. Performance tests show more than a tenfold signal increase for protein solutions and indicate that near‑100 % ion transmission efficiency is achievable.

Abstract

To improve upon the already impressive sensitivity achievable with electrospray ionization sources, a novel electrohydrodynamic ion funnel interface has been developed and implemented with a triple-quadrupole mass spectrometer. The ion funnel interface effectively consists of a series of ring electrodes of increasingly small internal diameters to which rf and dc electric potentials are coapplied. In the 1−10-Torr pressure range, the electric fields cause the collisionally damped ions to be more effectively focused and transmitted as a collimated ion beam. This paper describes the ion funnel design and presents an evaluation of its performance using a triple-quadrupole mass spectrometer. Ion transmission and m/z discriminating parameters (resulting in both effective low- and high-m/z cutoffs) are presented based upon both ion current measurements and mass spectra. Electrospray ionization mass spectra of selected protein solutions demonstrated well over 1 order of magnitude increase in signal relative to that of the instrument operated in its standard (inlet capillary−skimmer) configuration under similar conditions. The present results suggest that it will be feasible to realize close to 100% ion transmission efficiency for analytically relevant ions through the electrospray ionization interface and into the mass analyzer.