Illustration of the Selectivity of Collision Cross Section Ion Mobility Screening for the Analysis of Pesticide Residues in Food Using the ionKey/MS System

Significance of the Topic

Pesticide residue analysis in food faces increasing challenges due to the growing number of compounds, complex sample matrices, and stringent regulatory limits. High-resolution mass spectrometry provides specificity but can struggle with co-extracted matrix interferents. Integrating collision cross section (CCS) measurements via ion mobility adds an orthogonal dimension of separation based on ion size, shape, and charge, enhancing selectivity and confidence in residue screening.

• Complex food extracts require sensitive, selective methods
• CCS offers a robust physicochemical identifier
• Microfluidic chromatography (ionKey) improves ionization and reduces matrix suppression

Objectives and Study Overview

This work aimed to demonstrate the benefits of combining CCS screening with the Waters ionKey/MS System for pesticide residue detection in food. Key goals included: establishing CCS values for target pesticides; comparing performance to conventional UPLC-IM-MS; evaluating sensitivity, linearity, and false positive reduction; and creating a rapid workflow for proficiency test samples.

Methodology and Instrumentation

Samples (mandarin, ginger, leek, pear) were extracted by Ultra-Turrax in ammonium acetate/methanol, filtered, and matrix-matched calibrants prepared. Spiking levels ranged from 0.01 to 1.0 mg/kg with appropriate dilutions. Chromatography used the nanoACQUITY/ACQUITY UPLC M-Class System with iKey BEH C18 Separation Device at 45 °C (150 µm×100 mm, 1.7 µm), mobile phases water/acetonitrile (0.1% formic acid) and a gradient over 17 min. The SYNAPT G2-Si HDMS with ESI+ acquired TOF mass spectra (50–1200 m/z) and travelling wave ion mobility (N₂ drift gas, calibrated with polyalanine). Data were processed in UNIFI and MassLynx software.

Main Results and Discussion

Compared with conventional UPLC: the ionKey/MS System achieved 4× higher signal-to-noise and 3× greater response for indoxacarb, even with 10× sample dilution. Detection of pencycuron at 2 pg and 200 fg on column was demonstrated with <1 ppm mass error and <1% CCS deviation. Linearity in matrix-matched standards yielded r²≥0.95. CCS filtering (±2%) reduced 81 initial observations in an EU-RL proficiency sample to 9 true pesticide detections, avoiding reprocessing. Ion mobility alignment cleaned coeluting spectra, enabling selective fragment identification.

Benefits and Practical Applications

• Enhanced selectivity via CCS reduces false positives/negatives
• Improved sensitivity permits greater dilution, mitigating matrix effects
• Microfluidic chromatography offers routine, high-efficiency separations
• Generic workflows handle varied chromatographic retention shifts

Future Trends and Potential Applications

• Expansion of CCS libraries for broader compound coverage
• Integration of He and N₂ calibrations for cross-platform consistency
• Application to non-targeted screening and protomer identification
• Automation of CCS screening in regulatory laboratories

Conclusion

The ionKey/MS System combined with travelling wave ion mobility and CCS measurement significantly enhances pesticide residue screening by improving sensitivity, selectivity, and spectral clarity. This approach supports more reliable, high-throughput analysis in complex food matrices.

References

1. M. McCullagh et al. Exploring the Benefits and Potential of iKey Microfluidic Chromatography and Time-of-Flight Mass Spectrometry for Pesticide Residue Analysis. Waters Application Note 720005195en, 2014.
2. Waters Technical Note. The use of Collision Cross Section (CCS) Measurements in Food and Environmental Analysis. 720005374en, 2015.
3. M. F. Bush et al. Ion Mobility Mass Spectrometry of Peptide Ions: Effects of Drift Gas and Calibration Strategies. Anal. Chem. 84:7124–7130, 2012.
4. M. McCullagh et al. Collision Cross Section a New Identification Point for a “Catch All” Non-Targeted Screening Approach. Waters Application Note 720005055en, 2014.
5. M. McCullagh et al. Use of Ion Mobility Spectral Cleanup and Collision Cross Section Values to Increase Confidence and Efficiency in Pesticide Residues Screening Strategies. Waters Application Note 720005080en, 2014.
6. M. McCullagh et al. Discovery of Pesticide Protomers Using Routine Ion Mobility Screening. Waters Application Note 720005028en, 2014.