Analysis of Dithiocarbamate Pesticides by GC-MS

Significance of the Topic

The analysis of dithiocarbamate (DTC) fungicides is critical for ensuring food safety and complying with regulatory maximum residue limits (MRLs). DTCs are widely applied in agriculture due to their broad-spectrum activity and low acute toxicity, but they degrade into toxic carbon disulfide (CS2) and amines upon exposure to acid. Accurate measurement of total DTC residues, expressed as CS2 equivalents, supports risk assessment and quality control in the food supply chain.

Objectives and Study Overview

This study presents a robust, non-specific GC-MS method for quantifying total DTC residues in fruits and vegetables via acid hydrolysis to CS2. Thiram, a representative bis(dithiocarbamate), serves as the reference compound. Method validation covers sensitivity, precision, recovery, and applicability across multiple commodities including grapes, potatoes, tomatoes, chili, and eggplant.

Methodology and Instrumentation

Sample Preparation:

• Homogenize 25 g of produce; add SnCl2/HCl (1:1 v/v) and iso-octane.
• Incubate in a sealed bottle at 80 °C for 1 h with periodic inversion.
• Cool, centrifuge, and transfer the iso-octane layer for GC-MS analysis.

Calibration:

• CS2 stock (2000 µg/mL) in iso-octane; working standards at 0.04–1.30 µg/mL.
• Matrix-matched calibration prepared by spiking iso-octane extracts of blank commodities.

Used Instrumentation

• Thermo Scientific TRACE GC Ultra with PTV-LVI injector.
• ITQ 900 ion trap mass spectrometer operating in SIM mode (m/z 76, 78).
• Two column options evaluated: TG-624 (medium polarity) and TG-5MS (low polarity).

Results and Discussion

Sensitivity and Linearity:

• LOQ of 0.04 µg/mL and LOD of 0.005 µg/mL for CS2 (S/N > 10 and > 3 respectively).
• Calibration linearity R² = 0.9990 over 0.04–1.30 µg/mL.

Recovery and Precision:

• Recoveries ranged from 79 % to 104 % across all matrices at spike levels of 0.04, 0.16, and 1.30 µg/g.
• Repeatability and intermediate precision demonstrated RSD values within acceptable limits for routine analysis.

Interferences and Precautions:

• Natural CS2 precursors in brassica crops can cause false positives.
• Avoid rubber items during analysis to prevent contamination; use silicone or polyethylene.

Practical Benefits and Applications

This method integrates seamlessly into existing pesticide-residue workflows. It requires no specialized column beyond standard GC columns, and the SIM-based GC-MS detection offers high selectivity for CS2. Laboratories can adopt this procedure for routine monitoring of DTC residues in compliance with EU and international guidelines.

Future Trends and Opportunities

• Adoption of triple quadrupole or high-resolution MS could enhance specificity and lower detection limits.
• Automated sample hydrolysis and extraction could increase throughput.
• Extension to processed foods and feed commodities to assess DTC fate during processing.

Conclusion

A validated acid-hydrolysis GC-MS method provides reliable quantification of total DTC residues as CS2 in diverse food matrices. The approach meets sensitivity, accuracy, and precision requirements for regulatory compliance and food safety testing.

Reference

1. Crnogorac G., Schwack W. Residue analysis of dithiocarbamate fungicides. Trends Anal Chem. 2009;28(1):XX–XX.
2. Reynolds S. Analysis of Dithiocarbamates. SELAMAT Workshop, Bangkok. 2006.
3. EURL-SRM. Analysis of Dithiocarbamate Residues in Foods of Plant Origin involving Cleavage into CS2. 2010.
4. Amvrazi E.G. Fate of Pesticide Residues on Raw Agricultural Crops after Postharvest Storage and Food Processing. In: Stoytcheva M., editor. Pesticides – Formulations, Effects, Fate. 2011.