Chiral and Achiral Profiling of a Pesticide Formulation Using the ACQUITY UPC2 System and the ACQUITY QDa Detector

Importance of Topic

Pesticide formulations often contain chiral active ingredients where one enantiomer delivers the desired biological activity while the other may be less effective or carry unwanted effects. Accurate assessment of enantiomeric purity and detection of minor structural isomers is essential for product registration, environmental safety, and regulatory compliance. Supercritical fluid chromatography (SFC) coupled with mass detection offers a rapid, high-resolution alternative to traditional liquid chromatography methods, reducing analysis time and solvent consumption.

Objectives and Study Overview

This study aimed to develop and demonstrate a unified analytical workflow for both achiral and chiral profiling of a commercial triazole pesticide formulation. Using ultra-performance convergence chromatography (UPC²) on both achiral and chiral columns, combined with UV and mass detection via an ACQUITY QDa detector, the work sought to identify the major diastereomers of propiconazole and uncover minor isomeric impurities in a single platform.

Methodology and Instrumentation

Sample Preparation:

• Standards prepared in 50:50 acetonitrile/water.
• Formulation: 2 g sample extracted with 8 mL of 50:50 acetonitrile/water, sonicated 10 min, filtered through a 0.2 µm PVDF filter.

Instrumentation and Conditions:

• Chromatography: Waters ACQUITY UPC² System with multi-column switching.
• Achiral column: ACQUITY UPC² BEH 3.0 × 100 mm, 1.7 µm; flow 1.5 mL/min; ABPR 1990 psi; methanol co-solvent gradient (3–30% B over 4 min); column at 35 °C; UV detection at 220 nm; injection 0.5 µL.
• Chiral column: Amylose Chiral 3.0 × 150 mm, 2.5 µm; flow 2.0 mL/min; ABPR 1990 psi; 50:50 2-propanol/ethanol co-solvent gradient; UV detection at 220 nm; injection 1 µL.
• Mass detection: ACQUITY QDa Detector in ESI⁺; capillary 0.8 kV; cone 10 V; source 150 °C; desolvation 600 °C; scan 100–600 m/z; make-up solvent MeOH/water 98:2 with 0.1% ammonium hydroxide at 0.3 mL/min.
• Data system: Empower 3 FR2 for acquisition and Mass Analysis.

Key Results and Discussion

Achiral Separation:

• Detected two main propiconazole diastereomers (peaks 1 and 2) matching standard retention times.
• Observed two minor peaks (3 and 4) with identical UV spectra and MS isotopic pattern (m/z 342, dichlorinated) to propiconazole, suggesting structural similarity.

Chiral Separation:

• Amylose CSP resolved the two propiconazole diastereomers into four stereoisomeric peaks (1–4).
• Minor peaks from achiral run likewise resolved into four peaks (5–8) with matching chirality pattern, indicating a probable regioisomer related to the triazole ring.

Spectral Confirmation:

• Empower Mass Analysis view enabled simultaneous visualization of UV chromatograms, TIC, extracted ion chromatograms (XIC m/z 342), and aligned MS spectra.
• Combination of UV and MS detection improved selectivity, differentiating matrix interferences from isomeric peaks of interest.

Practical Benefits and Applications

• Rapid method development and analysis: achiral separations in <3 min versus 34–50 min by traditional HPLC.
• Reduced solvent use and waste: supercritical CO₂ primary mobile phase lowers reliance on hazardous organic solvents.
• Enhanced confidence in compound identification: cost-effective mass detection complements UV data.
• Single-platform workflow for both achiral and chiral profiling increases laboratory throughput.

Future Trends and Applications

• Isolation and structural confirmation of minor regioisomers to refine formulation quality control.
• Extension of UPC²-QDa methods to other chiral agrochemicals and environmental metabolites.
• Integration with high-resolution mass spectrometry for deeper structural elucidation.
• Adoption of greener co-solvents and automated method optimization guided by machine learning.

Conclusion

The combination of UPC² with UV and ACQUITY QDa mass detection provides a streamlined, high-throughput approach for achiral and chiral profiling of complex pesticide formulations. This platform rapidly distinguishes major diastereomers and uncovers minor stereoisomeric impurities, delivering enhanced selectivity, reduced solvent usage, and improved laboratory efficiency for regulatory and research applications.

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