Collision Cross Section Measurements in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) Based on the Flipping-Filtering Method

The ion collision cross section (CCS) is closely related to the structural and physical conformation of compounds, making it an ideal parameter for constructing databases. In recent years, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has gained widespread application in CCS measurements thanks to its ultra-high mass resolution and accuracy. Due to the collisions between ions and neutral molecules within the FT-ICR MS cell, the image current decays. Based on this feature, the ion CCS can be precisely calculated by applying corresponding collision models and algorithms. A new time-frequency analysis method is introduced: the flipping-filtering method based on the Levenberg–Marquardt algorithm. Before filtering, the data undergoes flipping and extension, effectively mitigating the issue of signal point waste commonly associated with traditional filtering techniques. This approach ensures a smooth and uninterrupted envelope of the image current signal while significantly enhancing the accuracy of decay factor and ion CCS measurements. Compared to the linewidth correction method and the line shape fitting method, this method exhibits superior noise resistance and resolution capabilities, serving as a valuable adjunct to ion CCS measurement techniques.