Multi-residue Pesticide Analysis in Onion by a Modified QuEChERS Extraction and Ion Trap GC/MSn Analysis

Importance of the Topic

The accurate quantification of modern pesticide residues in food matrices is essential for consumer safety and regulatory compliance. Newer active ingredients tend to be low molecular weight compounds designed for rapid environmental degradation. Consequently, sensitive sample preparation and detection strategies are required to address diverse chemical properties and achieve reliable monitoring in complex matrices such as onions.

Objectives and Study Overview

This study aimed to evaluate a modified QuEChERS extraction workflow coupled to tandem mass spectrometry on an ion trap GC/MS system for multi-residue pesticide analysis in onions. Key goals included establishing linear calibration ranges, limits of detection and quantitation, recovery performance, and method precision under regulatory guidelines.

Methodology and Sample Preparation

A homogenized onion sample was extracted using buffered acetonitrile in the presence of magnesium sulfate and sodium acetate to salt out aqueous components. Extracts underwent cleanup via dispersive solid-phase extraction with PSA and C18 sorbents, followed by evaporation and solvent exchange to a hexane/acetone mixture. An internal standard (d10-parathion) was added prior to instrumental analysis.

Instrumental Setup

• GC System: Thermo Scientific FOCUS GC with splitless injection mode and surge pressure (250 kPa) using a TRACE TR-35MS capillary column (35 % diphenyl/65 % dimethyl polysiloxane, 30 m × 0.25 mm × 0.25 µm, 5 m guard).
• Injection: 2 µL surge splitless injection at 250 °C to minimize thermal degradation and improve analyte transfer.
• Mass Spectrometry: Thermo Scientific ITQ 700 ion trap operating in MSn mode (Electron Ionization at 70 eV) with optimized precursor ion isolation, collision-induced dissociation voltages, and product-ion scanning for enhanced selectivity.
• Autosampler: AS 3000 configured for precise 2 µL injections and solvent rinsing routines.

Main Results and Discussion

Linearity was excellent for most pesticides (R2 > 0.995), covering calibration ranges up to 1200 ng/g. Average LOD and LOQ values in onion matrix were approximately 8 ng/g and 27 ng/g, respectively. Recoveries ranged from 79 % to 159 % (average 116 %), with method validation at 100–300 ng/g yielding mean recovery of 104 % and RSD of 22 %. Daily monitoring of endrin breakdown demonstrated stable system inertness (< 5 % product formation), indicating robust injection and column performance.

Benefits and Practical Applications

• The streamlined QuEChERS protocol reduces sample preparation time and consumable costs while maintaining high extraction efficiency across diverse pesticide chemistries.
• Ion trap MSn analysis offers superior matrix interference removal and confirmation capabilities in a single run, improving confidence at trace levels.
• Surge splitless injection minimizes analyte decomposition, extending maintenance intervals and enhancing laboratory throughput.

Future Trends and Possibilities for Use

Integration of high-resolution accurate-mass detection could further improve compound identification. Automation of QuEChERS workflows and expansion to additional produce and processed food matrices will support high-throughput monitoring. Potential development of portable GC-MS platforms may enable on-site screening, enhancing food safety surveillance.

Conclusion

The combined QuEChERS extraction and Thermo Scientific ITQ 700 GC/MSn method provides sensitive, accurate, and reproducible multi-residue pesticide analysis in onions. It meets stringent regulatory requirements, supports routine quality control, and reduces operational costs through efficient sample preparation and robust instrumentation.

References

1. AOAC Official Method 2007.01 Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate, S. Lehotay, Journal of AOAC International, 90(2), 485–520 (2007).
2. M. Okihashi, Rapid Method for the Determination of 180 Pesticide Residues in Foods by Gas Chromatography/Mass Spectrometry and Flame Photometric Detection, Journal of Pesticide Science, 30(4), 368–377 (2005).
3. Commission Decision 2002/657/EC Implementing Council Directive 96/23/EC Concerning the Performance of Analytical Methods and the Interpretation of Results, Official Journal of the European Communities (2002).
4. Codex Alimentarius MRL Database for Lettuce (www.codexalimentarius.net).