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

Importance of the topic

Ensuring the safety of green tea requires reliable detection of multiple pesticide residues at low levels. Newer pesticides tend to be smaller and degrade faster in the environment than legacy compounds, making sample preparation and sensitive analysis essential for accurate identification and quantification in complex herbal matrices.

Objectives and Study Overview

This work aimed to develop and validate a streamlined workflow combining a modified QuEChERS extraction with ion-trap GC/MSn for the simultaneous determination of 22 common pesticides in green tea. Key goals included establishing linear ranges, limits of detection (LOD) and quantitation (LOQ), recovery, precision, and compliance with international maximum residue limits (MRLs).

Methodology

The procedure followed a three-step QuEChERS approach:

• Extraction: Homogenize 15 g tea with water and extract with 1% acetic acid in acetonitrile; salt out using magnesium sulfate and sodium acetate.
• Cleanup: Remove polar interferents (caffeine and polyphenols) by sorbents (PSA, C18, MgSO₄).
• Solvent exchange: Evaporate to dryness and reconstitute in hexane/acetone (9:1) with an internal standard for injection.

Used Instrumentation

Analysis was performed on a Thermo Scientific TRACE FOCUS GC coupled to an ITQ 700 ion-trap mass spectrometer. A 35% diphenyl/65% dimethyl polysiloxane column (0.25 mm × 30 m, 0.25 µm) with a 5 m guard was used. Surge splitless injections at 250 °C minimized analyte breakdown. The ion trap operated in MS/MS mode with optimized collision-induced dissociation to enhance selectivity and lower background.

Main Results and Discussion

Calibration curves in matrix showed excellent linearity (R²>0.995 for most analytes). Average LODs were approximately 14 ng/g, satisfying stringent MRL requirements across regulatory bodies. Method validation at spike levels from 37.5 to 1 200 ng/g yielded mean recoveries of 104% and precision of 10.8% RSD. Daily system checks using endrin and DDT breakdown products demonstrated less than 15% degradation, confirming stable injector performance.

Benefits and Practical Applications

This combined QuEChERS–GC/MSn protocol offers:

• Rapid, cost-effective sample preparation with reduced solvent and consumable use.
• High sensitivity and selectivity through MS/MS fragmentation for accurate multi-residue quantification.
• Robust performance with minimal maintenance and compliance with international residue limits.

Future Trends and Opportunities

Advances may include automated QuEChERS platforms for higher throughput, expansion of analyte panels to emerging pesticides, integration with high-resolution mass spectrometry for non-target screening, and application of chemometric tools to improve data interpretation and real-time monitoring of herbal products.

Conclusion

The validated method achieves reliable multi-residue determination of diverse pesticides in green tea, meeting global regulatory standards with strong accuracy, precision, and operational efficiency. Its rugged performance and broad applicability make it suitable for routine food safety testing.

References

1. Lehotay, S. J. AOAC Official Method 2007.01: Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate. J. AOAC Int. 90(2), 485–520 (2007).
2. Okihashi, M. Rapid Method for the Determination of 180 Pesticide Residues in Foods by GC/MS and Flame Photometric Detection. J. Pestic. Sci. 30(4), 368–377 (2005).
3. European Commission. Commission Decision 2002/657/EC: Performance of Analytical Methods and Interpretation of Results. Official Journal L221, 8–36 (2002).
4. Codex Alimentarius. Pesticide Maximum Residue Limits for Tea. http://www.codexalimentarius.net/mrls/pestdes/jsp/pest_q-e.jsp.