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

Importance of the Topic

Tea is a widely consumed beverage and can accumulate pesticide residues which pose health risks. Rapid and reliable multi-residue analysis is essential for quality control and regulatory compliance. Methods that minimize sample preparation time while ensuring cleanup and instrument performance are critical for high-throughput testing in tea and other complex matrices.

Objectives and Study Overview

This study aimed to develop and optimize cleanup strategies following QuEChERS extraction for comprehensive pesticide residue analysis in dried tea. It evaluates three post-extraction protocols tailored for Ultra Performance Liquid Chromatography tandem Mass Spectrometry (UPLC-MS/MS) and Gas Chromatography tandem Mass Spectrometry (GC-MS/MS), focusing on base/neutral and acidic pesticides.

Methodology and Instrumentation

Sample Preparation:

• QuEChERS extraction: 2 g dried tea equilibrated with water, followed by 10 mL acetonitrile and CEN QuEChERS salts (DisQuE pouch). Centrifugation at 4 000 rpm.
• dSPE cleanup (base/neutral for UPLC-MS/MS): 1 mL extract with MgSO4/PSA/C18/GCB dSPE tube; centrifuge and dilute with mobile phase.
• SPE cleanup (base/neutral for GC-MS/MS): Dilute extract in acetone/toluene, pass through Sep-Pak PSA/Carbon cartridge with MgSO4 top layer; elute and concentrate.
• SPE cleanup (acidic pesticides by UPLC-MS/MS): Adjust pH to 7.5–8.5, use Oasis MAX cartridge with conditioning, wash, and elute with MTBE/methanol/formic acid; concentrate and reconstitute.

Instrumentation:

• ACQUITY UPLC I-Class with BEH C18 column (2.1 × 100 mm, 1.7 µm)
• Waters Xevo TQ-S Mass Spectrometer (ESI+/- for LC-MS/MS; APGC source for GC-MS/MS)
• Agilent 7890 GC with J&W DB-5MS column (30 m×0.25 mm×0.25 µm)
• DisQuE products (QuEChERS extraction and dSPE cleanup)
• Sep-Pak PSA/Carbon and Oasis MAX SPE cartridges
• MassLynx V4.1 with Quanpedia database

Main Results and Discussion

Recovery and Precision:

• UPLC-MS/MS with dSPE cleanup achieved recoveries of 70–115% (RSD ≤20%) for 29 pesticides at both 10 and 100 ppb levels. Matrix effects were below 35% except imidacloprid (45% suppression).
• GC-MS/MS with PSA/Carbon SPE cleanup delivered recoveries of 40–124% (RSD ≤28%) for 33 compounds at 10 and 100 ppb.
• Acidic pesticide (2,4-D) cleanup via Oasis MAX yielded 73% recovery at both spiking levels with low variability.

Cleanup Effectiveness:
The dSPE protocol extended LC-MS maintenance intervals from 20 to 100 samples. The GC SPE cleanup allowed hundreds of injections before port or column cleaning. MTBE-based elution in Oasis MAX selectively removed tea matrix acids without co-elution.

Benefits and Practical Applications of the Method

• Streamlined, high-throughput sample preparation for tea matrices.
• Flexible cleanup options for diverse pesticide chemistries.
• Extended instrument uptime and reduced maintenance costs.
• Compliant with EU and US MRLs, suitable for QA/QC laboratories.

Future Trends and Opportunities

As regulatory limits tighten and tea products diversify (e.g., herbal blends), robust multi-residue methods will be vital. Emerging materials for dispersive and cartridge cleanup may further improve selectivity. Integration with automated platforms and high-resolution mass spectrometry could enhance throughput and confirmatory analysis.

Conclusion

Optimized cleanup strategies after QuEChERS extraction enable reliable multi-residue pesticide analysis in dried tea by UPLC-MS/MS and GC-MS/MS. The tailored dSPE and SPE protocols provide high recoveries, low matrix interferences, and extended instrument performance, supporting routine monitoring and regulatory compliance.

References

Waters Corporation. Multi-Residue Pesticide Analysis in Tea: Optimized Cleanup After QuEChERS Extraction for UPLC-MS/MS and GC-MS/MS Analysis. Application Note; 2015.