Determination of Multi-Pesticide Residues in Dried Tea Samples using an Optimized Extraction/Cleanup Regime and the Agilent 7000 Series Triple Quadrupole GC/MS System

Significance of the Topic

Tea is one of the most consumed beverages worldwide and poses a complex analytical challenge due to its intricate matrix rich in polyphenols, caffeine and other coextractives. The widespread use of multiple classes of pesticides on tea plantations raises concerns for consumer safety and necessitates reliable residue control methods to comply with regulatory limits and ensure product quality.

Objectives and Overview of the Study

This application note describes the development and validation of an optimized extraction and cleanup procedure combined with high-sensitivity triple quadrupole GC/MS/MS to determine over 100 pesticide residues in dried tea. Key goals included reduction of matrix interferences such as caffeine, robust chromatographic performance through post-run backflush and attainment of detection levels well below EU maximum residue limits.

Methodology and Instrumentation

The sample preparation workflow employs a modified QuEChERS approach followed by liquid-liquid extraction:

• Hydration of 2 g dried tea with water followed by acetonitrile extraction with MgSO4, NaCl and an internal standard.
• Removal of semivolatile interferences by hexane partitioning and salt addition.
• Injection of cleaned extract into GC/MS/MS.

The analytical system consists of an Agilent 7890 GC with a capillary flow backflush module coupled to an Agilent 7000B triple quadrupole MS operated in MRM-EI mode. Retention time locking and optimized collision energies ensure confident identification and quantification.

Main Results and Discussion

Cleanup removes over 90 % of caffeine and other late-eluting coextractives, yielding stable retention times and peak shapes over 150 injections. Matrix-matched calibration down to 0.001 mg/kg achieves excellent linearity. Validation in green and black tea at spiking levels of 0.01, 0.1 and 1 mg/kg produced recoveries of 70–120 % and RSDs below 20 %, meeting SANCO guidelines. A pilot survey of 37 commercial teas detected residues in 81 % of samples, with cypermethrin, endosulfan and propargite most frequently found and occasional EU MRL exceedances identified.

Benefits and Practical Applications of the Method

• High throughput: over six samples per hour with minimal solvent use.
• Enhanced robustness: reduced carry-over and extended column life via backflush.
• Sensitive and reliable quantification at or below regulatory limits.
• Applicability to routine QA/QC in food safety laboratories.

Future Trends and Potential Applications

Emerging directions include integration with high-resolution mass spectrometry for non-target screening, further miniaturization and automation of sample prep, greener solvent-reducing protocols, and expansion to multi-residue methods in other complex food matrices.

Conclusion

The optimized QuEChERS-based extraction and GC/MS/MS method provides a robust, sensitive and efficient solution for multi-pesticide residue analysis in dried tea. It achieves reliable performance at EU MRL levels, addresses key matrix challenges and supports routine monitoring to protect consumer health.

Reference

1. Agilent publication on capillary flow technology and backflush (5990-3367EN).
2. Cajka T et al. Analytica Chimica Acta 742 (2012) 51–60.
3. Regulation EC No 396/2005 on pesticide MRLs.
4. SANCO 12495/2011 method validation guidelines.