Determination of pesticides in food extract samples at low ppb levels using a new bench top GC-MS/MS system

Significance of the Topic

The reliable detection and quantitation of pesticide residues at low parts-per-billion levels in food matrices are critical for ensuring consumer safety and meeting stringent regulatory standards. Complex sample matrices such as fruits, vegetables and animal fats introduce co-extractives that can compromise analytical sensitivity, specificity and instrument performance. Implementing advanced chromatographic and mass spectrometric techniques addresses these challenges and supports high-throughput monitoring in quality control and food safety laboratories.

Objectives and Study Overview

This study evaluates a new bench-top GC-MS/MS system for multi-residue pesticide analysis in challenging food extracts. Key aims include:

• Assessing the capability to detect, confirm and quantify 60 agrochemical analytes at 1–100 ppb levels.
• Comparing performance in two lettuce extracts and one pork fat extract prepared via QuEChERS.
• Demonstrating enhanced chromatographic robustness through capillary flow back-flushing.

Methodology

Matrix-matched calibration standards (1–100 ppb) were prepared in blank lettuce and pork fat extracts. Spiked samples (20 analytes per extract) were analyzed in triplicate. Key analytical parameters included:

• Gas chromatograph: Agilent 7890A with 30 m × 0.25 mm ID × 0.25 µm HP-5MS Ultra Inert column.
• Injection: 1 µL cold splitless injection via PTV inlet, automated by a 7683 auto-liquid sampler.
• Mass spectrometer: Agilent 7000A triple quadrupole operated in MRM mode with two transitions per analyte (quantifier and qualifier).
• Retention time locking to chlorpyrifos methyl at 16.59 min for reproducible scheduling of MRM events.
• Capillary flow back-flushing after each injection to eliminate high-boiling matrix residues and maintain column integrity.

Used Instrumentation

• Agilent 7890A gas chromatograph
• HP-5MS Ultra Inert capillary column (30 m × 0.25 mm ID × 0.25 µm)
• Agilent 7000A triple quadrupole mass spectrometer
• PTV inlet and Agilent 7683 auto-liquid sampler

Main Results and Discussion

Analysis of the pork fat extract yielded confirmation and quantitation of 19 out of 20 spiked analytes; folpet was not detected. Both lettuce extracts performed similarly, with the first extract reporting all 20 analytes and the second detecting 19 (folpet absent). Quantitative results closely matched spiked concentrations, demonstrating excellent accuracy and precision in the low-ppb range. Full-scan TIC comparisons confirmed that capillary flow back-flushing effectively removed co-extractives, preventing retention time shifts, peak tailing and ion source contamination.

Benefits and Practical Applications

Key advantages of this GC-MS/MS approach include:

• High selectivity and sensitivity for trace-level detection of diverse pesticide classes.
• Robust method performance in complex food matrices, reducing false negatives and positives.
• Improved instrument uptime and reproducibility through back-flushing maintenance.
• Streamlined sample analysis workflow suitable for routine QA/QC laboratories.

Future Trends and Potential Applications

Advancements may include coupling with high-resolution mass spectrometry for non-target screening, integration of automated sample prep to increase throughput, and miniaturized portable GC-MS/MS systems for in-field testing. Further method adaptations could target emerging contaminants and environmental matrices, broadening the scope of multi-residue analysis.

Conclusion

The integration of capillary flow back-flushing with a triple quadrupole GC-MS/MS platform offers a powerful, reliable solution for the multi-residue analysis of pesticides at trace levels in complex food extracts. This approach ensures accurate quantitation, sustained chromatographic integrity and instrument protection, meeting the demands of modern food safety testing laboratories.