a) Transmission curves for Leucine Enkephalin, Reserpine, Bradykinin and Ubiquitin ions as a function of pressure, using RF of 1.74 MHz and 40-170 Vp-p. Other charge states of Bradykinin and Ubiquitin showed similar transmission. The pressure in the 2nd ion funnel region was maintained at 2.0 Torr. Each data set is normalized to its individual highest intensity point. b) The transmission of high-pressure funnel when operated at 560 kHz, 70 Vp-p and 1.74 MHz, 50-80 Vp-p (adjusted for maximum transmission at each pressure). The pressure in the second ion funnel region was 1.3 Torr. The sample was standard Reserpine. Leucine Enkephalin, Bradykinin and Ubiquitin showed similar results.