Enantioselective Resolution and Analysis of Chiral Pesticides in Formulations by UltraPerformance Convergence Chromatography (UPC2) with UV Detection

Significance of the topic

Chiral pesticides often exhibit enantioselective behavior in target and non-target species. Accurate separation and quantification of their stereoisomers are essential for optimizing efficacy, minimizing environmental impact, and ensuring regulatory compliance.

Objectives and study overview

This study demonstrates rapid enantioselective resolution and analysis of two key chiral pesticides—metalaxyl-M and S-metolachlor—in commercial aqueous formulations. UltraPerformance Convergence Chromatography (UPC²) with UV detection was evaluated as a faster, more efficient alternative to traditional normal-phase HPLC.

Methodology and instrumentation

Sample preparation involved weighing two pesticide formulations, extracting with hexane, dichloromethane, or ethyl acetate, sonicating, and filtering through 0.2 µm PVDF. Standard solutions matched the sample diluent.

• System: Waters ACQUITY UPC² with PDA detector
• Software: Empower 3
• Column: CHIRALPAK IA-3 (4.6×150 mm, 3 µm)
• Mobile phase: Supercritical CO₂ with 2-propanol gradient
• Back pressure: 2000 psi (138 bar)
• Flow rate: 4.0 mL/min (metalaxyl-M), 2.5 mL/min (S-metolachlor)
• Column temperature: 55 °C (metalaxyl-M), 35 °C (S-metolachlor)
• Detection: UV at 215 nm (metalaxyl-M), 220 nm (S-metolachlor)
• Injection volume: 2 µL

Key results and discussion

Gradient UPC² achieved baseline resolution of metalaxyl-M enantiomers in ~1 min (Rₛ=2.47) versus ~15 min (Rₛ=1.94) in literature HPLC. S-metolachlor’s four stereoisomers eluted in ~4.5 min with Rₛ between 1.48 and 2.31, compared to 20–30 min previously.

Hexane proved the most selective extraction solvent for both formulations. Chromatograms showed clear separation from formulation matrix. Reproducibility over 6–100 injections yielded %RSD ≤1.34 for retention time, peak area, area %, and height. Notably, R-metalaxyl %RSD was 0.02 and S-metalaxyl 0.85; metolachlor stereoisomers ranged 0.55–1.34.

Benefits and practical applications

• Significantly reduced analysis time increases sample throughput
• Lower solvent consumption and waste disposal costs
• High resolution ensures accurate enantiomeric ratio measurements
• Robust method supports quality control in agrochemical production

Future trends and potential applications

UPC² may be extended to other chiral agrochemicals and coupled with mass spectrometry for deeper characterization. Continuous improvements in chiral stationary phases and greener mobile phases will further enhance efficiency and sustainability.

Conclusion

UltraPerformance Convergence Chromatography with UV detection provides a rapid, reliable, and environmentally friendly approach for chiral pesticide analysis, outperforming conventional HPLC in speed, resolution, and reproducibility.

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