Use of Ion Mobility Spectral Cleanup and Collision Cross Section Values to Increase Confidence and Efficiency in Pesticide Residues Screening Strategies

Significance of the Topic

Pesticide residue analysis in food commodities is critical to ensure consumer safety and regulatory compliance worldwide. Increasing global trade and diverse regulatory Maximum Residue Limits (MRLs) demand robust multi-analyte screening strategies capable of reliably detecting low-level contaminants amid complex matrices. Traditional high-resolution mass spectrometry approaches often require extensive manual data review to avoid false positives and negatives. Integrating ion mobility separation and collision cross section (CCS) measurements provides an orthogonal separation dimension and an additional confirmatory parameter, enhancing screening confidence and throughput.

Study Objectives and Overview

This study evaluates the feasibility of combining UPLC separations with high-definition ion mobility mass spectrometry (IMS-MS) on a Waters SYNAPT G2-S HDMS platform to improve pesticide residue screening. Objectives include:

• Assessing CCS values as a secondary point of identification alongside accurate mass, retention time, and fragment ions.
• Demonstrating ion mobility spectral cleanup to resolve co-eluting components and simplify spectral interpretation.
• Validating the workflow using matrix-matched standards, blank samples, and a European Proficiency Test FV-13 mandarin homogenate.

Used Instrumentation

The analytical platform comprised:

• ACQUITY UPLC I-Class System with BEH C18 column (100 × 2.1 mm, 1.7 µm).
• SYNAPT G2-S HDMS with electrospray ionization (ESI+) and TriWave ion mobility cell.
• MassLynx and UNIFI Software for data acquisition, CCS library creation, and automated screening.

Methodology

Sample Preparation:
10 g of homogenized fruit or vegetable matrix was extracted with 20 mM ammonium acetate in methanol, filtered, and diluted to 100 mL with 5 mM ammonium acetate in water.

Chromatography:
Gradient elution (0.1% formic acid in water/acetonitrile) at 0.45 mL/min, column temperature 45 °C, injection volume 5 µL.

Mass Spectrometry:
ESI+ mode, desolvation temperature 550 °C, cone voltage 20 V, mass range 50–1200 Da, acquisition rate 5 spectra/s. Ion mobility parameters: N2 drift gas, IMS wave velocity 650 m/s, wave height 40 V, gas flow 90 mL/min, duty cycle 10.8 ms, leucine enkephalin (m/z 556.2766) for lock mass. Collision energy ramp 10–45 eV.

Data Processing:
CCS values, accurate mass, retention time, and fragment ion information for pesticide standards were compiled into a UNIFI library. Non-targeted acquisitions of spiked and blank matrices were automatically screened using configurable tolerances for m/z, retention time, and CCS error.

Main Results and Discussion

CCS Screening Performance:
Application to European Proficiency Test FV-13 achieved 100% correct identifications under CCS-augmented criteria, with clear differentiation of target compounds.

False Detection Assessment:
A blank mandarin extract yielded >10,000 detected features, but stepwise filtering (±20 ppm m/z, ±0.5 min Rt, ±10% CCS) reduced candidates to 20 pesticides; tightening to <10 ppm mass error and ±2% CCS left only DEET, a known solvent contaminant.

Spectral Cleanup:
Ion mobility–resolved spectra enabled UNIFI’s 4D peak detection to extract single-component precursor and fragment ion spectra (e.g., thiabendazole at m/z 202), significantly cleaner than conventional 3D processing and facilitating rapid structural confirmation.

Benefits and Practical Applications

• Enhanced identification confidence through orthogonal CCS measurement, reducing false negatives and positives.
• Streamlined workflows with minimal manual data review by employing wider screening tolerances.
• Automated ion mobility spectral cleanup accelerates elucidation of co-eluting species across thousands of components per injection.
• Improved laboratory efficiency and compliance with SANCO/12571/2013 guidelines.

Future Trends and Opportunities

Expansion of CCS databases and integration with AI-driven data analytics will further automate non-targeted screening of emerging contaminants. Real-time CCS calibration and cloud-based spectral libraries can enable decentralized testing and rapid regulatory responses. Combining IMS-MS with orthogonal separation techniques (e.g., FAIMS, differential mobility) promises even greater selectivity for complex food matrices.

Conclusion

The integration of ion mobility separation and CCS values into routine UPLC-MS workflows provides a powerful orthogonal separation and confirmatory tool for pesticide residue screening. This approach enhances confidence, reduces manual intervention, and maintains compliance with regulatory standards while improving overall laboratory throughput.

References

1. Sanitary and Phytosanitary Quality Control Procedures for Pesticide Residues in Food & Feed, SANCO/12571/2013.
2. McCullagh M. et al., RAFA 2013 Poster: Collision Cross Section a New Identification Point, 2013.
3. McCullagh M., Cleland G., Hanot V., Stead S., Williams J., Goscinny S., Waters Application Note 720005055en, June 2014.
4. Hernandez F., Ibañez M., Sancho J.V., Pozo O.J., Anal. Chem. 76 (2004) 4349–4357.