Review of Ion Collision Cross Section Measurement Methods Based on Ion Trap Mass Spectrometry

In recent years, with the increasing demand for molecular structure analysis, the development of method for measuring ion collision cross sections (CCS) in a single ion trap mass analyzer has become a research hot topic. Measuring ion CCS in ion trap mass spectrometry does not require additional instrument modifications and experimental conditions, it is possible to measure ion CCS while obtaining a high-resolution mass spectrum. Reducing instrument complexity and obtaining molecular structure information when measuring highresolution mass, the method has gradually become an effective mean of measuring CCS. So far, Measuring ion CCS has been succeed in Fourier transform ion cyclotron resonance (FT-ICR) trap, Orbitrap, quadrupole ion trap (QIT), electrostatic linear ion trap (ELIT). Accurate measurement of ion motion decay in ion traps is the primary prerequisite for measuring ion CCS with ion trap mass spectrometers. The collision between ions and buffer gas is the main reason for ion motion decay. In particular, on the basis of the original ion collision models including the Langevin collision model, the hardsphere collision model, the mixed collision model, the energetic hardsphere collision model was developed. Ion motion under different experimental conditions is suitable for different collision models. Based on this, a lot of methods were developed to calculate ion motion decay curves including frequency domain, time domain and time-frequency analysis methods, thus enhancing accuracy and resolution of ion CCS measurement. However, there are still many challenges. Ion CCS measurement in ion trap mass spectrometry depends on true pressure in ion trap, however true pressure in ion trap can′t be measured precisely. Also, the ion CCS of the isomers can′t be measured separately in ion trap mass spectrometry yet. Therefore, the useful method to realize the CCS measurement of isomers urgently needs to be developed, and improving the resolution of CCS measurement in ion trap mass spectrometry will also be an important thing. Specially, the lower the pressure, the greater the ion kinetic energy, then the resolution of ion CCS measurement is better. The methods to get higher sensitivity detection electronics and lower pressure remain to be developed. Here, the theory of collision between ions and buffer gas molecules was expounded, then different methods for measuring ion CCS in ion trap mass spectrometry, and the advantages and disadvantages of the measurement methods were reviewed, the future research direction was prospected at last.