Determination of 287 Pesticides at Trace Levels by GCxGC–TOFMS

Significance of the Topic

Trace-level determination of pesticide residues in complex food matrices is essential for ensuring consumer safety, regulatory compliance and maintaining public trust. Advances in analytical instrumentation and data processing now allow rapid, comprehensive screening of hundreds of pesticides at parts-per-trillion levels, reducing preparation time and improving laboratory throughput.

Objectives and Overview

This study evaluates a comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC–TOFMS) approach for the simultaneous analysis of 287 pesticides at trace levels. The method aims to:

• Assess separation efficiency for complex mixtures
• Establish limits of detection and quantification
• Demonstrate rapid peak deconvolution for coeluting compounds

Methodology and Instrumentation

Sample preparation was based on minimal cleanup similar to QuEChERS dispersive solid-phase extraction, followed by direct injection. Instrumental setup included:

Used Instrumentation

• LECO Pegasus 4D GCxGC–TOFMS with GERSTEL CIS4 PTV injector
• First column: Rtx-CLPesticides II (30 m × 0.25 mm, 0.2 μm film)
• Second column: Rxi-17 (1.1 m × 0.1 mm, 0.1 μm film)
• Primary oven program: 95 °C (5 min), ramp to 200 °C @ 10 °C/min, ramp to 270 °C @ 7 °C/min, ramp to 320 °C @ 10 °C/min (10 min)
• Secondary oven offset +30 °C, similar ramp rates
• Modulation period: 5 s (0.6 s hot pulse)
• Carrier gas: helium at 26 psi
• Injection volume: 2 μL (CTC CombiPAL)
• Transfer line: 250 °C
• TOFMS: mass range 50–600 amu, acquisition rate 200 spectra/s, source at 200 °C

Results and Discussion

Retention times and limits of detection (LODs) were established using a 250 pg/µL standard. The GCxGC contour plot revealed extensive coelution in one-dimensional separation that was resolved orthogonally in the second dimension. Examples include four closely eluting pesticides separated by selective retention on the second column. The True Signal Deconvolution™ algorithm in ChromaTOF® software successfully extracted pure spectra from overlapping peaks. LODs ranged from approximately 0.06 pg/µL to tens of pg/µL, demonstrating suitability for regulatory requirements. Peak capacities and resolving power were significantly enhanced compared to one-dimensional GC.

Benefits and Practical Applications

• Simultaneous analysis of nearly 300 pesticides in a single run
• Enhanced separation minimizes false positives/negatives from coelution
• Reduced sample cleanup accelerates throughput and lowers solvent consumption
• Comprehensive data acquisition supports both targeted quantification and untargeted screening

Future Trends and Possibilities

Ongoing improvements may include:

• Automated sample preparation workflows integrated with GCxGC–TOFMS
• Machine-learning algorithms for automated peak identification and quantification
• Expansion to other classes of contaminants, such as pharmaceuticals and persistent organic pollutants
• Miniaturized modulators and faster electronics to further increase separation speed and sensitivity

Conclusion

The LECO Pegasus 4D GCxGC–TOFMS method provides a powerful and efficient platform for trace-level pesticide analysis in complex food matrices. Its high separation capacity, rapid spectral deconvolution and broad dynamic range support stringent regulatory compliance and high-throughput laboratory operations.

Reference

1. Commission Directive 2003/13/EC, Official Journal of the European Communities L41 (2003) 33.
2. Commission Directive 2003/14/EC, Official Journal of the European Communities L41 (2003) 37.
3. Anastassiades M., Lehotay S.J., Stajnbaher D., Schenk F.J., J. AOAC Int. 86 (2003) 412.