Pharmacokinetic Analysis Using iMScopeTM QT During Corn and Soybean Seed Treatment with Pesticides

Significance of the Topic

Seed treatments are critical in modern agriculture for protecting seedlings against pathogens while minimizing overall pesticide use. Label-free imaging of active ingredients in coated seeds offers direct insight into the spatial distribution and dynamics of these compounds, enabling formulation optimization and improved efficacy of seed-applied pesticides.

Objectives and Study Overview

This application note describes the use of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) on the iMScope QT platform to visualize the fungicide ethaboxam in corn and soybean seeds. The study compares distribution patterns before and five days after sowing to elucidate the pathways by which the seed treatment migrates into soil and seed tissues.

Methods and Instrumentation

• Seed Treatment: Soybean seeds (75 g a.i./100 kg) and corn seeds (37.5 g a.i./100 kg) were coated with 34.2 % ethaboxam solution in water.
• Cryosectioning: Treated and control seeds flash-frozen, embedded in carboxymethylcellulose, and sectioned at –20 °C to 15 µm thickness using cryofilm transfer onto indium tin oxide (ITO) slides.
• Matrix Application: α-Cyano-4-hydroxycinnamic acid deposited at 0.7 µm thickness via iMLayer™ at 250 °C.
• MALDI-MSI Analysis: Performed on iMScope QT in positive ion mode (m/z 300–330 for MS; 100–330 for MS/MS), laser power 65, spot size 2, 80 shots at 1 kHz. Data processed with IMAGEREVEAL™ MS software.

Applied Instrumentation

• iMScope™ QT atmospheric-pressure MALDI quadrupole time-of-flight mass spectrometer
• iMLayer™ matrix deposition system
• Cryostat (Leica CM1950) and cryofilm section transfer
• ITO-coated conductive glass slides
• IMAGEREVEAL™ MS data analysis software

Main Results and Discussion

• Standard Validation: Ethaboxam [M+H]+ at m/z 321.08 detected in positive mode with characteristic product ions at m/z 183.05, 200.07, and 237.08.
• Pre-Sowing Distribution: Both seed types show surface accumulation; corn also exhibited penetration into the germ tip and endosperm, whereas soybean retention remained superficial.
• Post-Sowing Dynamics: Five days after sowing, soybean seeds retained minimal ethaboxam on the coat and showed release into soil, with negligible internal translocation. Corn maintained epidermal accumulation and displayed marked migration into the embryo region.
• Quantitative Imaging: Ion intensity profiles revealed rapid decline of surface ethaboxam in soybean versus sustained epidermal signals and increasing internal levels in corn over five days.

Benefits and Practical Applications

• Provides spatially resolved, label-free insights into seed treatment delivery pathways.
• Enables comparative evaluation of different seed formulations and crop species.
• Supports targeted optimization of pesticide dose and coating methods to enhance efficacy and environmental safety.

Future Trends and Opportunities

• Extension to additional crops and active ingredients for broader agronomic applications.
• Integration with quantitative ion calibration for precise dose mapping.
• Combination with other imaging modalities and machine learning for predictive modeling of agrochemical dynamics.

Conclusion

The study demonstrates that MALDI-MSI on the iMScope QT platform effectively visualizes and distinguishes dynamic distribution patterns of ethaboxam in corn and soybean seeds before and after sowing. This technique offers a powerful tool for improving seed treatment strategies and understanding pesticide translocation in early plant development.

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