title: Analysis of high mass-to-charge ions in a quadrupole ion trap mass spectrometer via an end-cap quadrupolar direct current downscan.
abstract: A method for performing mass-selective instability analysis in a three-dimensional (3-D) quadrupole ion trap is described that involves scanning a direct current (dc) voltage applied to the end-cap electrodes while holding the radio frequency (rf) potential at a fixed value. Rather than eject at the ß(z) = 1 instability line by ramping the amplitude of the drive rf potential applied to the ring electrode, as with the original mass-selective instability scan, this approach effects ion ejection along the ß(z) = 0 instability line in a process identical in principle (though it varies in its method of implementation) to the previously termed "downscan" (       Todd  ,   J. F. J.     ;      Penman  ,   A. D.     ;     Smith  ,   R. D.       Int. J. Mass Spectrom. Ion Processes     1991  ,   106  ,   117 - 135  ). A linear scan of the dc amplitude results in a nonlinear mass scale, unlike the conventional resonance ejection scan with a linear scan of the rf amplitude, and the ejection of ions in the direction of high mass-to-charge (m/z) to low m/z. However, the downscan offers some advantages over the traditional rf scan for ions of high m/z values. These include a larger scannable mass range, as well as the opportunity for improved resolution at high mass. These characteristics are demonstrated with ions of m/z 10(4)-10(5).
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
authors.forename: Boone M
authors.initials: BM
authors.lastname: Prentice
authors.forename: Scott A
authors.initials: SA
authors.lastname: McLuckey