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

• Published in: Analytical chemistry (Washington) Vol. 70; no. 19; pp. 4111 - 4119
• Main Authors: Shaffer, Scott A, Prior, David C, Anderson, Gordon A, Udseth, Harold R, Smith, Richard D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.10.1998
• Subjects: Animals; Cattle; Chemistry; Cytochrome c Group - analysis; Erythrocytes - metabolism; Exact sciences and technology; Gramicidin - analysis; Horses; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Ions; Mass spectrometers and related techniques; Myocardium - metabolism; Myoglobin - analysis; Physics; Reproducibility of Results; Scientific imaging; Spectrometry, Mass, Secondary Ion - instrumentation; Spectrometry, Mass, Secondary Ion - methods; Ubiquitins - analysis; Performance evaluation; Ring electrode; Equipment interfaces; Mass spectroscopy; Instrument for chemical analysis; Biological macromolecule; Electrohydrodynamic ionization; Electrospray; Optimization; Quadrupole spectrometer
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac9802170

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.