Ion mobility calculations of flexible all-atom systems at arbitrary fields using two-temperature theory
Farah Mubas-Sirah1, Viraj D Gandhi1,2, Mohsen Latif1
1Department of Mechanical Engineering, Indiana University - Purdue University Indianapolis, Indianapolis, IN, USA. clarriba@iupui.edu.
Physical Chemistry Chemical Physics : PCCP
|January 16, 2024
Summary
This study introduces a new method for ion mobility spectrometry (IMS) calculations at high electric fields. The enhanced method accounts for ion structural changes, improving agreement with experimental data for large organic ions.
Area of Science:
- Physical Chemistry
- Analytical Chemistry
- Computational Chemistry
Background:
- Ion mobility spectrometry (IMS) separates ions by their movement in a gas under an electric field.
- Existing two-temperature theory for ion mobility has limitations with polyatomic ions and gases, especially at high electric fields.
- Previous studies showed deviations between theory and experiment for tetraalkylammonium salts above 100 Td.
Purpose of the Study:
- To develop and validate a modified high-field calculation method for ion mobility spectrometry.
- To investigate the impact of ion structural changes due to field heating on mobility measurements.
- To improve the agreement between theoretical predictions and experimental data for large organic ions.
Main Methods:
- A modified high-field calculation method was introduced, incorporating field-induced structural changes in ions.
- Molecular structures of tetraheptylammonium (THA+), tetradecylammonium (TDA+), and tetradodecylammonium (TDDA+) ions were generated at various temperatures using the MM2 forcefield.
- Ion mobility was calculated using the IMoS 1.13 software with the two-temperature trajectory method, considering multiple effective temperatures and a linear weighing system.
Main Results:
- The modified method, accounting for ion structural enlargement at high fields, showed better agreement with experimental mobility data.
- FAIMS (Field Asymmetric Ion Mobility Spectrometry) dispersion plots also demonstrated improved concordance with experimental findings.
- The study confirmed that ion structural changes significantly influence mobility at high electric fields.
Conclusions:
- Structural enlargement of ions due to field heating is a critical factor for accurate mobility calculations at high fields.
- The developed method enhances the predictive power of ion mobility spectrometry for complex organic ions.
- Further research is needed to fully address the complexities of inelastic collisions and energy transfer in ion-gas interactions.
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