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Using a Cyclic Ion Mobility Spectrometer for Tandem Ion Mobility Experiments
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Complementary methods for structural assignment of isomeric candidate structures in non-target liquid chromatography
Masoumeh Akhlaqi1, Wei-Chieh Wang1, Claudia Möckel1
1Department of Materials and Environmental Chemistry, Svante Arrhenius väg 16C, 114 18, Stockholm, Sweden.
Analytical and Bioanalytical Chemistry
|July 15, 2023
Summary
Identifying chemical structures using LC/IMS/HRMS is challenging due to isomers. This study found that even with analytical standards, pinpointing the correct structure among isomers remains difficult, highlighting the need for improved in silico prediction accuracy.
Area of Science:
- Environmental Chemistry
- Analytical Chemistry
- Computational Chemistry
Background:
- Non-target screening using Liquid Chromatography/Ion Mobility Spectrometry/High-Resolution Mass Spectrometry (LC/IMS/HRMS) is vital for detecting environmental and food contaminants.
- Structural assignment of detected chemicals is complicated by the presence of isomers, posing a significant challenge for both instrumental and computational methods.
Purpose of the Study:
- To evaluate the feasibility of structural assignment for isomeric compounds using in silico predictions and analytical standards.
- To determine the required accuracy of in silico methods for retention time and collision cross-section (CCS) predictions to effectively resolve isomeric ambiguities.
Main Methods:
- Investigated 14 candidate structures for five features in a spiked water sample using LC/HRMS.
- Compared in silico predicted retention times and database collision cross-section (CCS) values against empirical data from analytical standards.
- Analyzed reversed-phase LC retention times, ion mobility spectrometry separation, and high-resolution MS2 spectra of analytical standards.
Main Results:
- In silico predictions alone, even with uncertainty, could only rule out one of the isomeric structures, leaving annotation ambiguous.
- Reversed-phase LC provided the best separation for isomers, but ion mobility and MS2 spectra offered limited discriminatory power.
- Based on extensive data, a 95% reduction in candidate structures requires predicted retention time confidence intervals below 0.05 min and CCS confidence intervals below 0.15%.
Conclusions:
- Unequivocal structural annotation of isomers detected by LC/IMS/HRMS remains a significant challenge, even with available analytical standards.
- Improved accuracy in in silico prediction of retention times and CCS values is crucial for advancing non-target screening capabilities.
- This study establishes clear targets for in silico method development to overcome isomeric ambiguities in chemical analysis.
Keywords:
Cyclic IMSHigh-resolution mass spectrometryLiquid chromatographyMachine learningNon-targeted analysisWater analysisMore Related Videos
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