ION REMEASUREMENT IN THE RADIO-FREQUENCY QUADRUPOLE ION-TRAP

Multiple remeasurement of the same population of stored ions in a radi o frequency (rf) quadrupole ion trap is demonstrated, As the secular f requency of stored ions is swept across a fixed-frequency resonance ex citation signal via amplitude modulation of the confining rf voltage, the image current generated by the resulting coherent ion motion is me asured simultaneously with tuned-circuit, phase-sensitive defection, J udicious selection of the resonance excitation frequency and rf voltag e ramp limits enables the excitation-detection process to be performed over a range of mass-to-charge values, Furthermore, the inherent focu sing of the quadrupole held and use of helium buffer gas (similar to 1 0(-4) Torr) enable repeated scans to be made with negligible ion loss, For a collection of C3F5+ ions (m/z 131) produced via a single electr on ionization event, the remeasurement efficiency during 24 scans, as judged by the scan-to-scan loss in signal, was >99%.