Screening of Pesticides and Other Contaminants in Food Matrices Using a Novel High‑resolution GC/Q-TOF with a Low‑energy‑capable EI Source

Significance of the Topic

Modern food safety monitoring demands sensitive, high-throughput methods to detect trace levels of pesticides and contaminants in diverse food matrices. High-resolution gas chromatography quadrupole time-of-flight mass spectrometry (GC/Q-TOF) with low-energy electron impact (EI) ionization offers accurate mass identification and quantitation, addressing strict regulatory maximum residue limits and facilitating unknown compound confirmation.

Objectives and Overview

This study demonstrates the application of a novel high-resolution GC/Q-TOF system equipped with a low-energy-capable EI source to screen over 140 pesticides and other contaminants in organic and nonorganic food commodities. Key aims include evaluating method repeatability, linearity, mass accuracy, and the combined targeted and untargeted screening workflows.

Methodology

Sample Preparation:

• Extraction of homogenized food samples via QuEChERS (EN) protocol.
• Cleanup of lipid-rich avocado extracts using EMR-Lipid dSPE; pigment removal in broccoli via dSPE; general cleanup for fruits and vegetables.
• Spike of 140+ pesticides into organic matrices at 10–500 ng/mL for method evaluation; screening of nonorganic extracts without spiking.

Data Acquisition and Analysis:

• Agilent 7250 GC/Q-TOF with mid-column backflushing and retention-time locking.
• GC conditions: two Agilent HP-5 MS UI columns (15 m × 0.25 mm, 0.25 µm), MMI inlet, helium carrier gas.
• Temperature program: 60 °C (1 min), 40 °C/min to 170 °C, 10 °C/min to 310 °C (3 min); backflush post-run.
• EI ionization at 70 eV and low-energy 15 eV; mass range 45–650 m/z at 5 spectra/sec.
• Quantitation via Agilent MassHunter SureMass; targeted screening with a commercial pesticide library (850+ compounds); untargeted screening using NIST GC/MS library.

Used Instrumentation

• Agilent 7890B GC coupled to 7250 Q-TOF mass spectrometer
• Mid-column backflushing accessory
• QuEChERS EN extraction kits and EMR-Lipid dSPE materials
• MassHunter Data Analysis software B.08.00 with SureMass

Main Results and Discussion

• Retention time repeatability: SD ≤0.01 min across six replicates.
• Response repeatability: RSD typically below 15% across matrices.
• Matrix-matched calibration in avocado: over 85% of pesticides showed linearity (R2 ≥0.99) from 5–500 ng/mL; most others R2 ≥0.985.
• Mass accuracy: all detected pesticides measured within ±5 ppm at 10 ng/mL spiking levels.
• Targeted screening: quantified pesticides in nonorganic extracts with combined qualitative confirmation criteria (mass error <5 ppm, RT tolerance ±0.1 min, S/N ≥3).
• Untargeted screening: low-energy EI spectra preserved molecular ions, enhancing identification of non-library contaminants.

Benefits and Practical Applications

• Comprehensive multi-residue screening suitable for regulatory compliance.
• Rapid identification and quantitation without prior compound-specific methods.
• Enhanced confidence in unknown detection through low-energy EI molecular ion observation.

Future Trends and Applications

• Expansion of high-resolution libraries for broader contaminant coverage.
• Integration with automated workflows for real-time food safety monitoring.
• Development of even lower-energy ionization modes to improve structural elucidation of unknowns.

Conclusion

The high-resolution GC/Q-TOF platform with low-energy-capable EI provides a robust, sensitive, and versatile solution for simultaneous targeted and untargeted screening of pesticides and contaminants in various food matrices, meeting stringent analytical requirements and supporting food safety laboratories.

References

• Belmonte-Valles N., et al. Analysis of pesticide residues in fruits and vegetables using gas chromatography-high resolution time-of-flight mass spectrometry. Anal. Methods. 2015;7:2162-2171.
• Chen K., Nieto S., Stevens J. GC/Q-TOF Surveillance of Pesticides in Food. Agilent Technologies Application Note 5991-7691EN; 2016.