Analysis of Fungicide on the Peel Surface of Imported Oranges (1) — Identifying Substances by Simple Pretreatment and Accurate Mass Analysis

Significance of the Topic

A rapid and reliable approach for detecting post-harvest fungicide residues on imported citrus is essential to ensure food safety, comply with import regulations, and reduce inspection turnaround time. Simple sample preparation combined with high-resolution mass spectrometry can streamline screening workflows and support regulatory laboratories in maintaining product quality and consumer protection.

Goals and Study Overview

The study aims to evaluate a novel coupling of a Direct Probe Ionization Mass Spectrometer (DPiMS QT) kit with a quadrupole time-of-flight LCMS-9050 system to identify the fungicide enilconazole on the surface of orange peels. Key objectives include demonstrating minimal pretreatment steps, verifying accurate mass detection, and comparing results against a standard reference.

Methodology and Sample Preparation

Orange peel sections (5 × 5 mm, 1–2 mm thick) were placed in a biological sample plate and a micro-volume (35 µL) of extraction solvent was added through a port. The plate was folded to enclose the sample and positioned in the DPiMS QT system. Probe electrospray ionization (PESI) was used to sample a microdroplet from the peel surface, generating ions for injection into the Q-TOF mass analyzer. Analytical settings included an interface voltage of +2.50 kV, DL temperature 250 °C, heat block at 50 °C, and a scan range of m/z 50–1000 over 0.5 minutes.

Main Results and Discussion

Analysis of a 0.1 ppm enilconazole standard yielded a distinct protonated peak at m/z 297.0555, accompanied by its characteristic chlorine isotope pattern. The orange peel extract spectrum also displayed the same m/z signal and matching isotopic distribution, confirming the presence of enilconazole residues on the fruit surface. The high mass accuracy and resolution of the LCMS-9050 system ensured unambiguous identification without extensive chromatographic separation.

Benefits and Practical Applications

• Minimal sample processing reduces analysis time to under one minute per sample.
• High-resolution accurate mass detection allows confident identification of target molecules and their isotopes.
• Qualitative screening by DPiMS QT can triage samples prior to full LC/MS quantitation, optimizing resource use.
• Method adaptability supports a broad range of solid or biological surfaces that fit the sample plate.

Future Trends and Potential Applications

Advances in probe-based ionization combined with high-throughput data processing and machine learning could enable automated screening of multiple pesticide residues simultaneously. Miniaturized or field-deployable probe-MS systems may extend this approach to on-site inspections at ports of entry or in agricultural fields. Integration with robotic sample handling and AI-driven spectral libraries will further accelerate decision-making in quality assurance and regulatory compliance.

Conclusion

The combination of DPiMS QT direct probe ionization and LCMS-9050 Q-TOF accurate mass analysis provides a powerful, rapid, and easy-to-implement method for detecting post-harvest fungicide residues on citrus surfaces. Its minimal pretreatment requirements, high specificity, and flexibility make it an attractive tool for routine screening in food safety and industrial quality control laboratories.