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

Importance of the Topic

Green tea is widely consumed and may contain trace pesticide residues from agricultural practices. Accurate, efficient multi-residue analysis is crucial to ensure consumer safety and regulatory compliance. Combining a rapid sample preparation workflow with sensitive detection enhances laboratory throughput and data reliability.

Objectives and Study Overview

This study aimed to develop and validate a method for simultaneous determination of multiple pesticide residues in green tea. Key objectives included optimizing extraction and cleanup, establishing calibration ranges, determining detection limits, and evaluating method precision and accuracy.

Methodology and Instrumentation

Sample preparation followed a modified QuEChERS approach. Fifteen grams of homogenized tea were extracted with buffered acetonitrile, followed by salting out with magnesium sulfate and sodium acetate. A cleanup step removed caffeine and polyphenols, and solvent exchange to hexane/acetone (9:1) prepared extracts for injection. Matrix spikes at various levels (7.5 to 1 200 ng/g) were used to assess method detection limits and validation criteria.

Used Instrumentation

• Thermo Scientific ITQ 700 GC-ion trap mass spectrometer with MSn capability
• Thermo Scientific FOCUS gas chromatograph with splitless surge injection
• TRACE TR-Pesticide III capillary column (35% diphenyl 65% dimethyl polysiloxane, 0.25 mm x 30 m, 0.25 um film)
• AS 3000 II autosampler
• Standard consumables including splitless liners septa syringes and amber vials

Main Results and Discussion

Calibration curves in tea matrix showed excellent linearity for most compounds with correlation coefficients above 0.995. Limits of detection and quantitation met or surpassed international MRL requirements. Daily performance checks using endrin and DDT demonstrated breakdown below 15 percent indicating stable injector performance. Method validation yielded average recoveries of 104 percent and precision with RSD of 10.8 percent. MSn detection provided enhanced selectivity and minimized matrix interference.

Benefits and Practical Applications

• Single run analysis of over twenty pesticides
• Detection limits compliant with Codex EU and other regulatory bodies
• Surge splitless injection reduces analyte breakdown and maintenance needs
• QuEChERS workflow accelerates sample preparation and reduces solvent use

Future Trends and Applications

Future developments may include automation of QuEChERS processes for higher throughput, expansion of MSn libraries for emerging pesticides, portable GC MS systems for field testing, and adaptation of the workflow for other complex food matrices.

Conclusion

The integrated QuEChERS extraction and GC MSn method offers a robust sensitive and efficient solution for multi-residue pesticide analysis in green tea. It meets stringent regulatory criteria while minimizing system maintenance and maximizing laboratory productivity.

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 of August 12 2002 Implementing Council Directive 96 23 EC Concerning the Performance of Analytical Methods and the Interpretation of Results Official Journal of the European Communities 17 8 2002
4. MRLs for Tea as listed at http codexalimentarius net mrls pestdes jsp pest q e jsp