Multi-Residue Pesticide Analysis in Tea: Optimized Cleanup After QuEChERS Extraction for UPLC-MS/MS and GC-MS/MS Analysis

Significance of the Topic

The analysis of pesticide residues in dried tea is critical for ensuring consumer safety and meeting regulatory limits. Tea’s complex, highly resinous matrix presents unique challenges for residue extraction and cleanup prior to chromatographic analysis. Optimized methods reduce instrument downtime and improve detection reliability.

Objectives and Study Overview

This study aimed to develop a streamlined workflow based on the QuEChERS extraction technique, coupled with tailored cleanup protocols, for multi-residue pesticide analysis in black tea. Three distinct cleanup strategies were evaluated to accommodate acidic, neutral, and basic pesticides analyzed by UPLC-MS/MS and GC-MS/MS.

Methodology and Instrumentation

• Sample Preparation: 2 g of dried tea equilibrated with 10 mL water, extracted with acetonitrile and citrate-buffered QuEChERS salts.
• dSPE Cleanup for UPLC-MS/MS: 1 mL extract treated with MgSO4/PSA/C18/GCB blend to remove matrix interferences.
• PSA/Carbon SPE Cleanup for GC-MS/MS: 1 mL extract diluted in acetone/toluene, passed through PSA-carbon cartridge to eliminate colorants and lipophilic residues.
• Oasis MAX SPE Cleanup for Acidic Pesticides: 1 mL extract adjusted to pH 7.5–8.5 and processed on anion-exchange cartridge, eluted with MTBE/methanol/formic acid.
• Instruments: Waters ACQUITY UPLC I-Class with BEH C18 column, Waters Xevo TQ-S mass spectrometer (ESI and APGC), Agilent 7890 GC with DB-5 MS column.

Main Results and Discussion

Recovery values for over 30 pesticides ranged from 70 % to 115 % with RSDs below 20 % at both 10 and 100 ppb levels. Matrix effects were under 35 % for most compounds, except a 45 % suppression for imidacloprid. The citrate-buffered QuEChERS extraction efficiently isolated a wide polarity range of analytes, while targeted cleanup strategies significantly reduced matrix interferences and extended instrument maintenance intervals.

Benefits and Practical Applications

• High-throughput capability: over 100 LC-MS/MS runs without cone cleaning; hundreds of GC-MS/MS injections before port maintenance.
• Comprehensive multi-class pesticide coverage with reliable quantitation at regulatory limits.
• Adaptable workflow for laboratories focused on QA/QC, food safety, and regulatory compliance.

Future Trends and Opportunities

Emerging MS technologies, such as high-resolution and ambient ionization techniques, will further enhance sensitivity and reduce sample prep. Automation of cleanup steps and integration with on-line SPE modules can increase throughput. There is also growing interest in green solvents and sorbents to minimize environmental impact.

Conclusion

The optimized QuEChERS extraction, combined with targeted dSPE and SPE cleanups, provides a robust, reproducible approach for multi-residue pesticide analysis in tea. This workflow delivers high recoveries, low matrix effects, and reduced instrument maintenance, making it suitable for routine food safety monitoring.