CAPTAN AND FOLPET BY LC-MS/MS: IMPROVING IONISATION EFFICIENCIES OF MULTIRESIDUE PESTICIDES IN FOOD

Significance of the topic

Monitoring pesticide residues such as captan and folpet is essential for ensuring food safety and regulatory compliance. Traditional GC-MS methods suffer from rapid degradation of these thiophthalimide fungicides in the inlet, leading to poor reproducibility. A robust LC-MS/MS approach with optimized ionisation can overcome these limitations and streamline multi-residue screening in complex food matrices.

Objectives and overview of the study

The study evaluates electrospray ionisation (ESI) and the novel UniSpray (USI) source for the LC-MS/MS analysis of captan, folpet, and their degradation products (THPI, PI). Key goals include assessing method repeatability, sensitivity, linearity in kale and celery matrices, and compliance with EU maximum residue levels.

Methodology and instrumentation

• Sample preparation: matrix extraction and cleanup, spiked at trace levels (0.005–0.100 mg/kg).
• LC Conditions: ACQUITY UPLC I-Class, BEH C18 column (2.1×50 mm, 1.7 µm), 0.45 mL/min flow, 45 °C column, water/methanol mobile phases with 0.1% formic acid and 0.05% ammonia.
• MS Conditions: Xevo TQ-XS with ESI and UniSpray sources; ESI capillary 3 kV, desolvation 200 °C; USI impactor 3 kV, desolvation 300 °C, 1000 L/hr spray.

Main results and discussion

• GC-MS splitless injections of captan degraded rapidly over three consecutive runs; LC-MS/MS with ESI and USI remained stable over 25 injections (RSD <10%).
• Both ionisation modes yielded excellent linearity in matrix (R² >0.995) across 0.005–0.100 mg/kg.
• UniSpray delivered higher peak areas and improved ionisation efficiency compared to ESI for all analytes.
• Limits of detection in kale and celery: USI ≤5 ppb, ESI ≤5 ppb, well below EU MRLs (0.030–0.060 mg/kg).

Benefits and practical applications

• Eliminates degradation and reproducibility issues inherent to GC-MS for captan and folpet.
• Single LC-MS/MS workflow covers multiple fungicides and metabolites.
• Meets stringent sensitivity and regulatory requirements for food safety testing.

Future trends and potential applications

Atmospheric ionisation innovations like UniSpray may extend to broader pesticide classes, enhancing multi-residue methodologies. Integration with high-throughput LC-MS/MS platforms can support routine QA/QC in agricultural and food testing laboratories. Continued research into ionisation mechanisms and nanoflow interfaces promises further gains in sensitivity and robustness.

Conclusion

The developed LC-MS/MS methods using ESI and UniSpray effectively address the degradation challenges of captan and folpet observed in GC-MS. UniSpray offers superior ionisation, delivering robust, sensitive, and compliant analysis of thiophthalimide fungicides in food matrices.

Reference

• A. Berthet et al., Anal Bioanal Chem, 2011.
• A. Lubin et al., J. Am. Soc. Mass Spectrom, 2016.
• A. Lubin et al., J. Pharm. Biomed. Anal, 2017.
• European Union Commission Regulation (EU) 2016/156.