GCxGC-ECD of Organochlorine Pesticides in Cucumber and Tomato

Significance of the Topic

The determination of organochlorine pesticide residues in fruits and vegetables remains critical for food safety and dietary risk assessments, especially at trace levels. Comprehensive two-dimensional gas chromatography (GCxGC) coupled with an electron capture detector (ECD) offers enhanced separation capacity and sensitivity to address coelution challenges in complex food matrices.

Objectives and Study Overview

This study aimed to demonstrate the applicability of GCxGC-ECD to quantify low-level organochlorine pesticides in cucumber and tomato extracts. Key objectives included method validation through spike-and-recovery experiments and evaluation of detection limits and linearity.

Methodology and Instrumentation

• Sample preparation followed a modified multiresidue protocol: homogenization of a 50 g sample with 100 mL acetonitrile, C18 cartridge cleanup, salt partitioning, evaporation, and reconstitution in acetone.
• Instrumentation:
  • GCxGC system: LECO GCxGC modulator coupled to an Agilent 6890 GC with ECD.
  • Primary column: 10 m × 0.18 mm × 0.20 µm Rtx-5.
  • Secondary column: 1.1 m × 0.10 mm × 0.10 µm DB-17.
  • Carrier gas: Helium at 2 mL/min constant flow; injection 1 µL split 20:1 at 250 °C.
  • Oven programs: Primary 40 °C to 290 °C at 10 °C/min; secondary offset +10 °C; modulation time 4 s.
  • Detector: ECD at 325 °C with N2 makeup gas at 148 mL/min, 50 Hz.

Main Results and Discussion

• Contour and surface plots illustrated clear separation of multiple organochlorine pesticides even at sub-picogram levels on-column.
• Calibration for Endosulfan II was linear from 0.2 to 200 pg/µL, with a 20:1 split achieving an on-column detection of 10 fg.
• Unspiked cucumber and tomato extracts revealed trace concentrations (ppt to low ppb) of several pesticides; spike recoveries around 20 pg/µL confirmed method accuracy.
• Signal-to-noise ratios exceeded 600:1 for 1 pg on-column spikes, demonstrating high sensitivity.
• Persistent residues such as beta-HCH and Endosulfan II were detected, reflecting environmental and agricultural usage patterns.

Benefits and Practical Applications

• Enhanced peak capacity reduces coelutions of analytes and matrix interferences in complex food extracts.
• Thermal focusing sharpens peaks, improving detection limits crucial for regulatory monitoring.
• The method supports reliable quantification for dietary risk assessments and quality control in food analysis laboratories.

Future Trends and Potential Applications

• Integration with mass spectrometry for unambiguous compound identification and confirmation.
• Automation and high-throughput platforms for routine screening of broader pesticide panels.
• Adaptation to other food matrices and environmental samples to monitor emerging contaminants.
• Application in regulatory frameworks to ensure compliance with tightening residue limits.

Conclusion

The GCxGC-ECD approach delivers superior separation and sensitivity for trace-level organochlorine pesticide analysis in produce. Its robustness and low detection limits make it a valuable tool for food safety laboratories facing complex sample matrices.