Analysis of Dithiocarbamate Pesticides in Tea Using GC/MS/MS

Importance of the Topic

Tea is a widely consumed beverage globally, with India as the second largest producer. Fungal pathogens, particularly tea gray blight, can devastate yields up to 46%. Dithiocarbamate fungicides are routinely applied to manage these diseases, but their residues, monitored as total carbon disulfide (CS2), must comply with stringent maximum residue limits (MRLs) for food safety. Reliable analytical techniques are therefore essential to ensure regulatory compliance and consumer protection.

Objectives and Overview

This study presents a comprehensive method for quantifying total dithiocarbamate residues in tea by converting them to CS2 and analyzing via gas chromatography coupled with tandem mass spectrometry (GC/MS/MS). The aim was to achieve a quantification limit of 10 ppb in tea matrix, establish linear calibration (5–100 ppb) with R² > 0.999, and recoveries above 85%, using both single ion monitoring (SIM) and multiple reaction monitoring (MRM) modes on Agilent instrumentation.

Methodology and Instrumentation

Sample preparation involved:

• Weighing 10 g of tea and adding 50 mL of water.
• Supplementing with 20 mL isooctane and 75 mL acidified SnCl₂ solution.
• Heating at 80 °C for 1 hour with periodic shaking to liberate CS₂.
• Cooling, centrifuging, and filtering 2 mL of the supernatant for analysis.

Analytical configuration:

• GC: Agilent 7890/8890 with multimode inlet and HP-5ms UI columns (15 m × 0.25 mm, 0.25 µm), split mode (15:1) with a multibaffled liner.
• MS/MS: Agilent 7000D/E or 7010C, SIM of m/z 76 and 78 and MRM transitions (76→44/46, 78→44/46).
• Backflush: Reversed carrier flow to purge high-boiling tea matrix interferences, reducing run time and preserving column integrity.

Main Results and Discussion

Matrix-matched calibration (5–100 ppb) showed excellent linearity (R² ≥ 0.999) in both SIM and MRM modes. The method achieved a 10 ppb quantification limit (equivalent to µg/kg in tea) and detected CS₂ down to 5 ppb. Recoveries at 10 ppb ranged from 85% to 100%, with repeatability RSDs below 4.2%. Backflush effectively removed late-eluting matrix peaks and shortened total analysis time, enhancing throughput.

Benefits and Practical Applications

This GC/MS/MS approach offers:

• High sensitivity and specificity for dithiocarbamate residues in complex tea matrices.
• Compliance with stringent MRLs and rapid sample turnaround.
• Compatibility with existing pesticide workflows by updating acquisition methods only.

Future Trends and Applications

Advancements may include integration of high-resolution mass spectrometry for improved selectivity, microextraction techniques to minimize solvent use, and automation of sample preparation. Extending this workflow to other food matrices and real-time monitoring platforms could further strengthen residue surveillance.

Conclusion

The described GC/MS/MS method reliably quantifies total dithiocarbamate residues in tea at ppb levels with robust linearity, recovery, and precision. Implementation of backflush and optimized injection parameters ensures efficient separation from matrix interferences and high sample throughput, supporting regulatory compliance and quality control.

References

• Tea Board of India. State/Region Wise Tea Production Data for 2022.
• Joshi S.D. et al. Molecular Characterization of Pestalotiopsis spp. in Tea. Indian Journal of Biotechnology, 2009, 8, 377–383.
• European Commission. Pesticide Maximum Residue Levels Database.
• FSSAI. Food Safety and Standards Authority of India, QA/3/2021/FSSAI-Part(3).
• Community Reference Laboratories: EURL Single Residue Methods for Dithiocarbamates, GC-ECD.
• EURL-SRM Analytical Observations Report: CS₂ Hydrolysis Method Version 3.
• Agilent Technologies. GC Inlets: An Introduction, Publication 5958-9468EN, 2005.
• SANTE 11312/2021v2: Guidelines for Pesticide Residue Analysis in Food and Feed.