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

Significance of the topic

The accurate determination of captan and folpet residues in food products is essential for consumer safety and regulatory compliance. These thiophthalimide fungicides pose analytical challenges due to rapid thermal degradation during gas chromatography, leading to inconsistent results and potential underreporting of residue levels.

Objectives and Study Overview

This study aimed to develop and validate a robust liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for quantifying captan, folpet, and their degradation products tetrahydrophthalimide (THPI) and phthalimide (PI) in complex food matrices. Both electrospray ionization (ESI) and a novel UniSpray ionization (USI) source were evaluated to overcome limitations of traditional GC analysis.

Methodology and Instrumentation

A quick extraction and cleanup protocol was applied to kale and celery samples, followed by LC-MS/MS analysis. Key instrumental settings included:

• Liquid chromatography: ACQUITY UPLC I-Class system, ACQUITY BEH C18 column (2.1×50 mm, 1.7 µm), 45 °C, 10 µL injection, flow rate 0.45 mL/min, gradient from 90:10 to 0:100 water/methanol with 0.1% formic acid and 0.05% ammonia.
• Mass spectrometry: Xevo TQ-XS system using both ESI (3 kV capillary, 200 °C desolvation) and USI (3 kV impactor voltage, 300 °C desolvation, Coanda-effect sampling).

Results and Discussion

GC analysis of captan showed rapid in-source degradation within two consecutive injections, whereas the LC-MS/MS approach delivered excellent repeatability (RSD <10% for 25 injections in matrix). Calibration curves in kale and celery across 0.005–0.100 mg/kg achieved R²>0.995. Limits of detection (LOD) were well below EU maximum residue levels (MRLs): captan and folpet at 0.03–0.06 mg/kg. USI provided 2–5× higher signal intensities compared to ESI, further improving sensitivity and robustness.

Benefits and Practical Applications

The developed LC-MS/MS method eliminates degradation artifacts common in GC-MS, ensuring accurate quantification of parent compounds and metabolites in routine food monitoring. Its high throughput and low detection limits support quality control, regulatory testing, and research applications in agricultural and environmental analysis.

Future Trends and Applications

Integration of novel ionization sources like UniSpray with high-resolution mass spectrometry promises further gains in sensitivity and selectivity for multi-residue screening. Automation of sample preparation and expansion to other thermally labile pesticides could broaden the method’s utility across diverse food and environmental matrices.

Conclusion

An LC-MS/MS strategy using both ESI and UniSpray ionization has been established for reliable detection of captan, folpet, THPI, and PI in food samples. The approach offers superior repeatability, sensitivity, and regulatory compliance compared to conventional GC-MS methods.

References

• A. Berthet et al., Anal Bioanal Chem, 2011, 399.
• A. Lubin et al., J. Am. Soc. Mass Spectrom, 2016, 28.
• A. Lubin et al., J. Pharm. Biomed. Anal, 2017, 142.
• EU Commission Regulation (EU) 2016/156.
• EU Commission Regulation (EU) 2016/452.