Practical Implementation of Instantaneous Frequency Mass Spectrometry

We demonstrate instantaneous frequency (IF) mass spectrometry (MS) for the analysis of ion signals collected by image charge detection. We illustrate IFMS for ion motion frequency estimation based on instantaneous spectral analysis for the first time with experimentally-collected ion signals. This approach allows the observation of time-varying frequency estimates in contrast to typical Fourier transform mass spectrometry (FTMS) which provides constant frequency estimates of spectral peaks. We illustrate this approach for signals of quadrupole-selected ions collected with an Orbitrap mass spectrometer. We observe time-varying frequency phenomena in all ion transient signals and note an interesting observation with regard to the isotopologue signals of caffeine. While the source of this time-varying phenomena has yet to be determined, to the best of our knowledge, this is the first observation of such behavior in an Orbitrap system utilizing IF analysis. Finally, we provide deviation statistics of the IF from the FFT estimate using our entire dataset and demonstrate that the time-averaged IF is in general agreement with the frequency estimates provided by the FFT.