Improvement to Targeted and Untargeted Pesticide Residue Analysis: Fast and Flexible Analyte Finding For GC-MS and GCxGC-MS

Significance of the Topic

In contemporary food safety and environmental analysis, the number and variety of pesticide residues requiring monitoring have surged, driven by diversified agricultural practices and emerging global markets. Analytical workflows capable of both targeted quantitation and untargeted screening are essential to detect known contaminants and discover unexpected or novel residues in complex matrices such as food extracts.

Objectives and Study Overview

This work demonstrates a streamlined method for simultaneous targeted and non-targeted pesticide residue analysis using one-dimensional (1D) GC-MS and two-dimensional GCxGC-MS on a Pegasus BT 4D system. The goals were to reduce the number of injections, simplify method updates, and enhance detection sensitivity and specificity across a large compound panel.

Methodology and Instrumentation

Sample Preparation:

• QuEChERS extraction of spinach matrix spiked with a multi-residue pesticide mix (0.2–2000 ng/g).
• Unfortified extract analyzed to detect incurred pesticide residues.

Chromatographic and Mass Spectrometric Conditions:

• Gas Chromatograph: Agilent 7890A with LECO second oven and quad-jet thermal modulator.
• Primary Column: 30 m × 0.25 mm × 0.25 µm Rxi-5MS; Secondary Column: 1 m × 0.25 mm × 0.25 µm Rtx-200.
• Injection: 1 µL splitless at 225 °C; carrier gas He at 1.4 mL/min.
• Mass Spectrometer: LECO Pegasus BT 4D, ion source 250 °C, mass range 45–560 m/z, 8 spectra/s in 1D, 280 spectra/s in GCxGC.
• Oven Program: Primary 75 °C (1 min) to 320 °C at 10.2 °C/min; secondary oven +5 °C offset; modulation period 2 s.

Used Instrumentation

• LECO Pegasus BT 4D GCxGC-TOF MS with StayClean® ion source and ChromaTOF® software.
• Agilent 7890A GC with dual-oven and thermal modulator.

Main Results and Discussion

Target Screening Performance:

• Calibration linearity (R² ≥ 0.995) achieved for halogenated pesticides over 0.2–5.0 ng/g limits of quantitation in spinach matrix.
• Ionic ratios and accuracy within ±20% (LOQ) and ±30% (ion ratios), meeting regulatory criteria.

Workflow Simplification:

• Automated generation of target compound lists and user library entries via a graphical interface reduced manual setup.
• Combined Target Analyte Finding (TAF) and Non-Target Deconvolution (NTD) allowed both known and unknown peaks to be processed in one run.

Chromatographic Resolution Gains:

• GCxGC separation improved peak focusing, enabling clear discrimination of Chloroneb from matrix interference, boosting sensitivity and quantitation accuracy.
• 1D data often missed low-level compounds; GCxGC consistently detected and quantified trace pesticides with high spectral fidelity.

Discovery of Incurred Residues:

• Untargeted screening identified two fungicides, Permethrin isomers, and a plastic UV stabilizer in the unfortified spinach extract.
• Detected incurred compounds were easily added to the target list for subsequent quantitative analysis.

Benefits and Practical Applications

• Single-injection approach reduces analysis time, solvent use, and instrument wear.
• Automated target list management allows quick updates when new pesticides emerge or matrices change.
• High-resolution GCxGC provides robust data for regulatory compliance, QA/QC laboratories, and research settings.
• Non-targeted detection supports screening for contaminants beyond pre-defined lists, improving food safety surveillance.

Future Trends and Potential Uses

• Integration of machine learning within deconvolution software may further enhance non-target peak identification and reduce false positives.
• Expansion of high-throughput GCxGC-MS workflows into routine monitoring, driven by miniaturization and automation of sample handling.
• Application to other complex matrices such as environmental samples, pharmaceuticals, and biological tissues for comprehensive residue profiling.

Conclusion

The described workflow on the Pegasus BT 4D platform offers a unified solution for targeted quantitation and untargeted discovery of pesticide residues. By leveraging advanced deconvolution algorithms and two-dimensional chromatography, laboratories can achieve superior sensitivity, spectral fidelity, and operational flexibility while minimizing methodological complexity.

Reference

No external reference list was provided in the source document.