Eliminating Harmonic False Peaks in Fourier Transform Ion Mobility Spectrometry Using a Virtual Ion Gate

Fourier transform ion mobility spectrometry (FT-IMS) is a widely used modulation technique that improves ion utilization efficiency compared with conventional pulsed IMS, making it particularly effective for analyzing weak signals. However, traditional FT-IMS encounters significant challenges with harmonic false peaks, which arise from inherent limitations in the modulation and demodulation algorithms, ultimately compromising the accuracy of broad-spectrum analysis. Furthermore, the physical ion gate at the exit of the drift tube contributes to an approximate 20% loss of ions. In this study, these issues are addressed by replacing the physical ion gate with a virtual ion gate and optimizing the fundamental modulation waveform of FT-IMS based on the unique characteristics of the virtual ion gate. By orthogonalizing the fundamental wave, we eliminate the energy component associated with excess frequencies. This modification not only mitigates ion loss but also effectively resolves the harmonic false peaks problem inherent in traditional FT-IMS.