Direct chiral resolution and its application to the determination of fungicide benalaxyl in soil and water by high-performance liquid chromatography

A simple chiral high-performance liquid chromatography (HPLC) method with ultraviolet (UV) and circular dichroism (CD) detection was developed and validated for measuring benalaxyl enantiomers using (R,R) Whelk-O 1 column. The effects of mobile phase composition and column temperature on the entioseparation were investigated. A CD detector was used to determine the elution order of the enantiomers. Excellent resolution was easily obtained using n-hexane-polar organic alcohols mobile phase. The chiral recognition mechanism was also discussed. Based on the developed chiral HPLC method, enantioselective analysis methods for this fungicide in environment matrix (soil and water) were developed and validated. Good linearities were obtained over the concentration range of 0.25-25 mg L⁻¹ for both enantiomers. Liquid-liquid extraction and solid phase extraction (SPE) were used for the enrichment and cleanup of soil and water samples. Recoveries for the two enantiomers were 79-91% at 0.02, 0.04 and 0.2 mg kg⁻¹ levels from soil, and 89-101% at 0.0025, 0.01 and 0.05 mg L⁻¹ levels from water. Run-to-run and day-to-day assay precisions were below 10% for both enantiomers at concentrations of 0.5, 1 and 5 mg L⁻¹. Individual detection limits of the two enantiomers were both 2 ng. Limits of detection (LOD) were 0.004 mg kg⁻¹ in soil and 0.001 mg L⁻¹ in water.