A Strategy for Simultaneously Improving Resolution and Sensitivity of Hybrid Quadrupole Ion Trap/Time-of-Flight Mass Spectrometry Using Square Waveform Phase Modulation

The hybrid quadrupole ion trap/time-of-flight mass spectrometry (QIT/TOFMS) device is popular because of its advantages of high sensitivity, high resolution, and MS/MS capability. However, the analytical performance of QIT/TOFMS is severely limited by the parameters of the ion trap, as QIT is typically used as a TOF pulser because the ion initial distributions of space, velocity, and angle change dynamically with the phase angle of rf voltage. In this work, a square waveform phase modulation strategy was proposed to eliminate the influence of the rf phase angle, and the dependence of QIT/TOFMS performance on the phase angle was studied. It was found that the mass resolution and signal intensity showed a "W" trend with the increase of the ion extraction phase angle from 0 degrees to 360 degrees, where the best resolution and sensitivity were obtained at 0 degrees, 180 degrees, and 360 degrees while the worst resolution and sensitivity were obtained at 90 degrees and 270 degrees. Moreover, the optimum phase angle was independent of m/z. As a result, the mass resolution for m/z 106, 164, and 258 was improved by 162%, 160%, and 210% respectively, while the signal intensities for m/z 106, 164, and 258 were enhanced by 25 +/- 1, 10 +/- 1, and 21 +/- 1 fold, respectively, and a limit of detection down to 0.015 ppbv for m/z 164 was obtained. The experiment results indicated that the square waveform phase modulation strategy could be used to simultaneously improve the resolution and sensitivity of QIT/TOFMS.