NACRW 2017: A NEW STRATEGY FOR THE DETERMINATION OF CAPTAN AND FOLPET IN FOOD MATRICES

Importance of the Topic

Reliable monitoring of pesticide residues in food is essential to ensure consumer safety and regulatory compliance. Captan and folpet, two thiophthalimide fungicides, are notoriously challenging to analyze by GC-MS due to rapid degradation, leading to irreproducible results and potential underestimation of residues.

Study Objectives and Overview

This work aimed to develop and validate an LC-MS/MS method using electrospray ionization (ESI) and a novel UniSpray (USI) ion source to achieve repeatable, sensitive, and robust quantification of captan, folpet, and their degradation products THPI and PI in complex food matrices such as kale and celery.

Methodology and Instrumentation

• Sample Preparation: QuEChERS-style extraction followed by cleanup tailored to leafy and stalk vegetables.
• Chromatography: ACQUITY UPLC I Class with an ACQUITY BEH C18 column (2.1 × 50 mm, 1.7 µm); gradient elution from high aqueous to high organic phase.
• Mass Spectrometry: Xevo TQ-XS operated in MRM mode. Comparison of ESI and UniSpray ionization to assess ionization efficiency and repeatability.

Used Instrumentation

• LC System: Waters ACQUITY UPLC I Class
• Mass Spectrometer: Waters Xevo TQ-XS
• Ion Sources: Electrospray Ionization (ESI) and UniSpray (USI) atmospheric pressure ionization source

Key Results and Discussion

• Repeatability: LC-MS/MS injections (n=25) of captan and folpet in matrix yielded RSDs below 10%, whereas GC splitless injections showed rapid degradation within three injections.
• Linearity: Calibration in matrix from 0.005 to 0.100 mg/kg gave R²>0.995 for all analytes.
• Sensitivity: USI LODs in solvent were 0.1–1 ppb for THPI and PI and 0.5 ppb for captan and folpet. In kale and celery matrices, LODs remained well below EU MRLs (0.030 mg/kg for kale, 0.060 mg/kg for celery).
• Ionization Efficiency: UniSpray produced higher peak areas and lower variability compared to ESI, improving detection of both parent compounds and metabolites.

Practical Benefits and Applications

• Enhanced Robustness: Elimination of analyte degradation during analysis ensures reliable quantification.
• Regulatory Compliance: Sensitivity and repeatability meet EU maximum residue level requirements.
• Workflow Efficiency: Single LC-MS/MS method replaces multiple GC and LC workflows, reducing instrument time and method complexity.

Future Trends and Opportunities

• Expansion to Other Challenging Analytes: Application of UniSpray to a broader range of non-polar pesticides and metabolites.
• Integration with High-Throughput Platforms: Automation of sample preparation and data processing for large screening studies.
• Method Transferability: Adaptation to different food matrices and instrumentation platforms to support global monitoring programs.

Conclusion

An LC-MS/MS approach employing both ESI and UniSpray ionization provides a reliable, sensitive alternative to GC-MS for the analysis of captan, folpet, and their degradation products in food. The method demonstrates excellent repeatability, linearity, and detection limits well below regulatory thresholds, offering laboratories a robust solution for routine pesticide surveillance.

References

1. A Berthet et al. Anal Bioanal Chem 2011;399: LC/APCI-MS/MS method for captan and folpet metabolites.
2. A Lubin et al. J Am Soc Mass Spectrom 2016;28: Comparison of high voltage target and ESI.
3. A Lubin et al. J Pharm Biomed Anal 2017;142: Atmospheric pressure ionization using high voltage target.
4. European Union Commission Regulation (EU) 2016/156: MRLs for boscalid, clothianidin, thiamethoxam, folpet.
5. European Union Commission Regulation (EU) 2016/452: MRLs for captan, propiconazole, spiroxamine.