THE BENEFITS OF GAS-PHASE COLLISION CROSS-SECTION (CCS) MEASUREMENTS IN HIGH-RESOLUTION, ACCURATE-MASS UPLC/MS ANALYSES

Significance of the Topic

The rotationally averaged collision cross section offers a unique, orthogonal dimension for characterizing ion structure and conformation in the gas phase. By combining CCS measurements with high resolution accurate mass UPLC/MS, analysts gain enhanced selectivity and confidence in compound identification across diverse applications, from small molecule screening to structural proteomics.

Goals and Study Overview

This work explores the benefits of integrating gas-phase CCS determination via traveling wave ion mobility spectrometry into routine high-resolution UPLC/MS workflows. The study demonstrates improvements in peak capacity, the ability to resolve isomers and conformers, reduction of false positives and negatives in residue screening, and insights into molecular architecture in complex samples.

Methodology and Instrumentation

• Calibration of IMS drift times with reference ions of known CCS to derive accurate measurements.
• Implementation of traveling wave ion mobility separation within a quadrupole time of flight mass spectrometer.
• Complementary use of UltraPerformance LC for chromatographic retention and accurate-mass detection for orthogonal confirmation.

Instrumentation Used

• Waters SYNAPT G2-Si HDMS mass spectrometer equipped with T-Wave ion mobility separations.
• UltraPerformance liquid chromatography system for sample separation.

Main Results and Discussion

• CCS values provided separation of ions with identical mass and charge but different three-dimensional conformations, improving method selectivity.
• Pesticide screening in fruit extracts showed CCS reproducibility within two percent across multiple matrices, sharply reducing false positive and false negative identifications when used as a filtering criterion.
• Structural isomers, conformers and protomers were resolved, enabling confident identification in MALDI imaging and direct analysis experiments.
• Comparison of experimental and theoretical CCS values yielded insights into protein complex architecture, oil sample distributions and drug metabolite structures far faster than traditional techniques.

Benefits and Practical Applications

Incorporating CCS measurements enhances peak capacity and orthogonal selectivity in LC/MS methods. Gas-phase CCS serves as a robust, matrix-independent identifier for small molecules, pesticides, peptides, proteins and complex biomolecules. Key applications include targeted screening, imaging mass spectrometry, structural proteomics, environmental analysis and drug metabolism investigations.

Future Trends and Opportunities

• Development of comprehensive CCS databases and predictive computational models for rapid compound annotation.
• Integration of machine learning to refine CCS-structure relationships and improve prediction accuracy.
• Advances in ion mobility instrumentation for higher resolution and faster separations.
• Expanded use of CCS in metabolomics, lipidomics, native mass spectrometry and real-time process monitoring.

Conclusion

Gas-phase CCS measurement via traveling wave ion mobility delivers a powerful, orthogonal separation dimension that significantly increases analytical performance in high-resolution UPLC/MS workflows. It reduces ambiguous identifications, resolves structural isomers and provides unique structural insights, positioning CCS as a transformative tool in analytical chemistry.

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