Ion rotating motion in a gas‐filled radio‐frequency quadrupole ion guide as a new technique for structural and kinetic investigations of ions

An ion rotating excitation mode of operation of a segmented gas-filled radio-frequency quadrupole (RFQ) ion guide for a high-resolution orthogonal time-of-flight (TOF) mass spectrometer is described. It is shown theoretically, by computer simulation and experimentally, that ion rotating excitation in a gas-filled RFQ has several advantages over other types of ion oscillation excitation. The main advantages are an approximately twofold increase in average ion kinetic energy for the same maximal deviation from the RFQ axis and therefore an increase of about this factor of average internal excitation energy of ions, and the extended mass range of fragment ions that can be observed. The new method of ion decomposition by ion rotation around the axis of an RFQ ion guide was experimentally implemented and tested using a home-built ‘SIN-COS’ generator to supply the excitation voltage. This generator enables control of phase shift and amplitude of excitation voltages applied to quadrupole rods smoothly from the data acquisition program running on a PC. Copyright © 2001 John Wiley & Sons, Ltd.