AN ION FUNNEL INTERFACE FOR IMPROVED ION FOCUSING AND SENSITIVITY USING ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

To improve upon the already impressive sensitivity achievable with ele ctrospray ionization sources, a novel electrohydrodynamic ion funnel i nterface has been developed and implemented with a triple-quadrupole m ass spectrometer. The ion funnel interface effectively consists of a s eries of ring electrodes of increasingly small internal diameters to w hich rf and de electric potentials are coapplied. In the 1-10-Torr pre ssure range, the electric fields cause the collisionally damped ions t o be more effectively focused and transmitted as a collimated ion beam . This paper describes the ion funnel design and presents an evaluatio n of its performance using a triple-quadrupole mass spectrometer. Ion transmission and m/z discriminating parameters (resulting in both effe ctive low- and high-m/z cutoffs) are presented based upon both ion cur rent measurements and mass spectra. Electrospray ionization mass spect ra of selected protein solutions demonstrated well over 1 order of mag nitude 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 re alize close to 100% ion transmission efficiency for analytically relev ant ions through the electrospray ionization interface and into the ma ss analyzer.