Considerations for Generating Frequency Modulation Waveforms for Fourier Transform-Ion Mobility Experiments

By casting the information regarding an ion population’s mobility in the frequency domain, the coupling of time-dispersive ion mobility techniques is now imminently compatible with slower mass analyzers such as ion traps. Recent reports have detailed the continued progress toward maximizing the efficiency of the Fourier transform ion mobility-mass spectrometry (FT-IM-MS) experiments, but few reports have outlined the intersection between the practical considerations of implementation against the theoretical limits imposed by traditional signal processing techniques. One of the important concerns for Fourier-based multiplexing experiments is avoiding signal aliasing as a product of undersampled signals that may occur during data acquisition. In addition to traditional considerations such as detector sampling frequency, the limitations (i.e., maximum measurable drift time) imposed by experimental mass scan duration and the frequency sweep used for ion gate modulation must also be assessed. This work aims to connect the fundamental underpinnings of FT-IM-MS experiments and the associated experimental parameters that are encountered when coupling the comparatively fast separations in the mobility domain with the slower m/z scanning common for ion-trap mass analyzers. In addition to stating the relevant theory that applies to the FT-IM-MS experiment, this report highlights how aliased signals will manifest post Fourier transform in reconstructed arrival time distributions and calculated mobilities.