Alternative Representation for the Stability Diagram of Quadrupole Ion Traps upon Additional Quadrupolar Excitation

Abstract

We present a combined theoretical and experimental study of the stability of ions in a linear ion trap under the application of one or two auxiliary radiofrequency (RF) fields, in order to perform simultaneous resonant excitation/ejection of several different ions. The influence of the amplitude and frequency of the auxiliary field is addressed through the construction of experimental and theoretical stability diagrams. Theoretical diagrams are constructed using the method developed by Konenkov et al. [J. Am. Soc. Mass Spectrom. 13, 597 (2002)]. We propose a new representation of stability diagrams more adapted to the study of auxiliary excitations than the canonical one. Stability regions are represented as a function of the fundamental RF amplitude and of the relative intensity of the excitation. This representation facilitates the monitoring of the evolution of the mass-selectivity of first- and higher-order resonant excitations in the trap, for which an empirical law is derived. We also show that the relative phase shift between the excitation field and the main driving field has a strong influence on the shape of the diagrams.

Quadrupole mass filter operation with dipole direct current and quadrupole radiofrequency excitation

“…Vernier et al proposed another form of the presentation of stability islands using coordinates q ex , q at a given excitation frequency ν . The island positions on the ( q ex , q ) plane were verified experimentally …”

Mass filter with phase modulation of radio frequency voltage

“…Practical applications have used operation of a mass filter in a stability island at the top vertex of the upper quadrangle of the stability region to design a quadrupole mass spectrometer for space exploration 15,16 . Other results concerning quadrupole resonance excitations have already been presented in previous papers 17,18 …”

“…15,16 Other results concerning quadrupole resonance excitations have already been presented in previous papers. 17,18 This work will focus on the ion optical characteristics such as resonance frequencies, stability islands, mass peak shape, resolution, acceptance, admissible disturbance working parameters based on the analytical description, and numerical simulation of the ion motion.…”