Multi-Residue Method for Determination of 85 Pesticides in Vegetables, Fruits and Green Tea by Stir Bar Sorptive Extraction and Thermal Desorption GC-MS

Significance of the Topic

Pesticide residues in fruits, vegetables and tea pose health and environmental risks due to toxicity, persistence and bioaccumulation. Conventional multi-step sample preparations are time-consuming and may lack sensitivity. The development of a streamlined, high-throughput method that can detect multiple pesticide classes at low µg/kg levels is essential for routine monitoring and quality control in food safety and environmental analysis.

Objectives and Study Overview

This study aimed to establish and validate a multi-residue method for the simultaneous determination of 85 pesticides (chlorinated, carbamate, phosphorous, pyrethroid and other classes) in tomatoes, cucumbers, soybeans, spinach, grapes and green tea. The approach combines stir bar sorptive extraction (SBSE) with thermal desorption (TD) and retention-time-locked gas chromatography-mass spectrometry (RTL-GC-MS) to achieve high sensitivity and broad analyte coverage.

Methodology and Instrumentation

Sample Preparation:

• Homogenize 25 g of sample with 100 mL methanol.
• Ultrasonic extraction (20 min), centrifugation (3000 rpm, 5 min).
• Dilute supernatant twofold and fivefold with purified water.
• Perform SBSE at 24 °C for 60 min, stirring at 1000 rpm with PDMS-coated stir bars.

Thermal Desorption and GC-MS:

• Desorb two stir bars simultaneously in a GERSTEL TDU (20 °C→280 °C ramp) into a GERSTEL CIS PTV (−150 °C to 280 °C).
• Separate on a HP-5ms capillary column with RTL-calibrated oven program.
• Detect by scan-mode EI-MS (m/z 40–500) on an Agilent 6890N/5973N system.

Key Findings and Discussion

Effect of Methanol Dilution:
Testing dilution factors (1.7–20×) showed that twofold and fivefold dilution balances partition coefficients and adsorption losses for compounds across log Kow 2.8–7.4, maximizing recovery.

Analytical Performance:

• Linear calibration for 66 analytes over 4–100 µg/kg (r² > 0.99).
• LODs of 0.6–26 µg/kg for most pesticides (3.36× SD of low-level replicates).

Application to Real Samples:
Analysis of 25 market samples detected residues in 12 samples. Concentrations ranged from low µg/kg to ~1.8 mg/kg; all but one result fell below Japanese MRLs.

Benefits and Practical Applications

• Solvent-reduced workflow with combined extraction and preconcentration.
• High enrichment (~100×) and sensitivity for diverse pesticide chemistries.
• Streamlined automation: simultaneous desorption of two stir bars cuts analysis time.
• Reliable quantitation at regulatory levels in complex food matrices.

Future Trends and Potential Applications

• Expansion to emerging and polar pesticide classes via tailored sorptive coatings.
• Integration with tandem or high-resolution MS for enhanced selectivity.
• Miniaturization and on-site testing using portable SBSE-TD-MS platforms.
• Fully automated sample-to-report workflows for high-throughput monitoring programs.

Conclusion

The SBSE-TD-RTL-GC-MS method enables efficient, sensitive multi-residue analysis of 85 pesticides in fruits, vegetables and tea with minimal sample preparation. Its high throughput and low detection limits make it well suited for routine food safety screening and regulatory compliance.

References

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