Analysis of Antifungal Agent on Surface of Imported Orange

Importance of the Topic

The importation of agricultural produce such as citrus fruits into Japan involves long transit times during which spoilage and fungal growth can occur. Postharvest fungicides like enilconazole are often used to prevent mold during transport. Since Japan prohibits unauthorized postharvest chemicals in food products, rapid screening methods to detect such residues directly on the fruit surface are crucial. The ability to perform simple, rapid inspections can accelerate quarantine clearance, reduce logistics costs, and ensure food safety.

Objectives and Study Overview

This application note demonstrates the use of a direct probe ionization mass spectrometry system (DPiMS-2020) with probe electrospray ionization (PESI) to detect enilconazole on the skin of imported oranges. It aims to:

• Establish a straightforward sample preparation workflow for orange skin analysis.
• Verify the detection of enilconazole under direct probe ionization conditions.
• Assess spatial variability of residue distribution on the fruit surface.

Methodology and Instrumentation

Sample Preparation Workflow:

1. Cut a 5 mm square of orange peel (1–2 mm thick).
2. Place the peel between the halves of a specialized biological sample plate with the target surface facing upward.
3. Fold and close the plate to enclose the sample.
4. Add 35 µL of solvent into the plate hole and proceed to analysis.

Instrumental Conditions:

• Probe electrospray ionization (PESI) via DPiMS-2020 direct probe ionization mass spectrometer.
• PESI drive settings: sampling position –44.5 mm; probe speed 250 mm/s; voltage application during ionization.
• Mass spectrometry settings: positive ESI mode, interface voltage +2.45 kV, DL temperature 250 °C, block temperature 50 °C, scan speed 5000 µ/s.

Main Results and Discussion

The standard enilconazole sample produced a clear ion at m/z 297. Analysis of orange skin at two sampling sites revealed enilconazole at one location but not the other, indicating heterogeneous residue distribution likely due to uneven spraying. The isotopic pattern of enilconazole confirmed its identification. These findings illustrate that the DPiMS-2020 approach can rapidly detect trace fungicide residues with minimal sample handling and discern spatial distribution on the fruit surface.

Benefits and Practical Applications

The direct probe ionization technique offers:

• Rapid, simple sample preparation without extraction or chromatography.
• Point-specific analysis to locate residues on complex surfaces.
• Potential as a frontline screening tool to pre-select samples for quantitative follow-up by LC-MS/MS.
• Reduced inspection time, facilitating faster clearance of imported produce.

Future Trends and Potential Applications

The DPiMS-2020 and PESI approach may expand to:

• Screening a wide range of postharvest chemicals on various produce types.
• Integration with robotic sampling platforms for high-throughput inspection.
• Quantitative adaptation with internal standards and calibration curves.
• On-site testing in ports or distribution centers for real-time monitoring.

Conclusion

The study demonstrates that direct probe ionization mass spectrometry can effectively and rapidly confirm the presence of enilconazole on imported orange skin with minimal sample preparation. This screening method improves efficiency in food safety inspections and can be extended to quantitative LC-MS/MS protocols. Its adaptability to different sample types suggests broad applicability for monitoring postharvest chemical residues in the food supply chain.