Al-Fakih Ali Mohammed,Chaohong Feng,Ting Jiang,Wei Xu
Miniaturized mass spectrometers, with their increasing portability and performance enhancements, play a crucial role in selectively analyzing target compounds within complex mixtures, particularly in situ environments. As part of our ongoing efforts to enhance the analytical capabilities of the custom-built "brick" mass spectrometer, this study compared and optimized methods for ion isolation using Stored Waveform Inverse Fourier Transform (SWIFT) and Grid-SWIFT waveforms. The efficacy of the SWIFT and Grid-SWIFT waveforms in selective ion isolation was investigated, and through optimization of both waveforms, improved ion isolation efficiency, and peak resolution were demonstrated by adjusting waveform duration and amplitude. The results conclusively showed that Grid-SWIFT outperforms traditional SWIFT waveforms in enhancing the isolation of target ions. Additionally, a novel simulation-based approach was developed to simulate the behavior of ion trajectories under the SWIFT and Grid-SWIFT waveforms within LIT to provide a theoretical basis for better performance of the Grid-SWIFT waveforms. Results show that longer waveform durations help reduce energy leakage, providing higher isolation efficiency. Grid-SWIFT waveforms exhibited significantly less energy leakage compared to SWIFT waveforms. Consequently, using Grid-SWIFT as isolation waveforms improved the mass spectra' intensity and resolution.
Besides portability and increasingly improved performances, the ability of screening target analyte from complex compounds is a crucial function of miniature mass spectrometers, especially for in situ analysis. Selected reaction monitoring (SRM) and multiple reaction monitoring (MRM) operation modes are the most widely used mass spectrometry operation methods for target analyte quantitation. As a continuous effort to improve the analytical performances of the “brick” mass spectrometer, built in-house, pseudo-SRM and pseudo-MRM modes were realized on the linear ion trap mass analyzer in the device. A broadband excitation waveform in both time and frequency domains, namely, the Grid-SWIFT waveform, was constructed and compared with the conventional SWIFT waveform. By isolating target ions during the ion introduction period using the Grid-SWIFT waveform, target ions could be efficiently accumulated inside the ion trap without experiencing space charge effects and interferences from nontarget ions in the samples. As a result, not only the detection sensitivity of the target analyte could be increased, but also the quantitation accuracy over a relatively wide concentration range could be improved.
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