Ion funnels 48f (FIGS. 3C, 4C) can increase ion transmission by at least an order of magnitude over simple capillary inlets. See, e.g., A. Shaffer, K. Tang, G. A. Anderson, D. C. Prior, H. R. Udseth, R. D. Smith. Rapid Communications in Mass Spectrometry, 1997, 11, 1813-1817. An ion funnel typically has a stack of ring electrodes with decreasing inner diameters, using a combination of RF and DC potentials to focus ions. See, e.g., Kim, T.; Tolmachev, A. V.; Harkewicz, R.; Prior, D. C.; Anderson, G.; Udseth, H. R.; Smith, R. D.; Analytical Chemistry, 2000, 72, 2247-2255; and Julian, R. R.; Mabbett, S. R.; Jarrold, M. F. Journal of the American Society for Mass Spectrometry, 2005, 16 (10), 1708-1712. However, some ion funnels can be planar. See, e.g., US Patent Application Publication Serial Number 2013/0120894, the contents of which are hereby incorporated by reference as if recited in full herein. Ion funnels traditionally operate in a pressure range from 0.1 to 20 Torr. An RF potential is applied to every other electrode (“even electrodes”), and a 180° out-of-phase RF potential of the same magnitude is applied to the other electrodes (“odd electrodes”). A linear DC gradient is applied to both even and odd electrodes, with the highest magnitude voltage being applied to the entrance electrode, and the lowest being applied to the exit electrode. A separate “DC-only” electrode may be placed between the exit of the funnel and the mass analyzer. See, e.g., U.S. Pat. Nos. 6,107,628 and 7,351,964, the contents of which are hereby incorporated by reference as if recited in full herein.
