Ping Zhang,Qian Yu,Yuhan He,Wentao Zhu,Zhiqiang Zhou,Lin He
The enantiomeric separation of fenpropathrin enantiomers on Lux Cellulose-1, Lux Cellulose-3 and Chiralpak IC chiral columns as well as enantioselective degradation of fenpropathrin in soil were investigated by reverse-phase high-performance liquid chromatography (RP-HPLC). The effects of the chiral stationary phase, mobile phase component, mobile phase ratio, temperature and thermodynamic parameters on resolution were carefully evaluated. Fenpropathrin enantiomers achieve a baseline separation (Rs = 2.30) on the Lux Cellulose-3 column with a mobile phase of methanol/water at a ratio of 85/15. Partial separations were achieved on Lux Cellulose-1 and Chiralpak IC columns with maximum Rs = 1.01 and Rs = 0.64, respectively. Enantioselective degradation of fenpropathrin enantiomers in soil was investigated based on the proposed separation method. The half-life (t1/2) of S-fenpropathrin and R-fenpropathrin was 17.8 days and 12.6 days, respectively, indicating that the degradation of fenpropathrin in soil was enantioselective, with R-fenpropathrin preferentially degraded. Furthermore, the formation and degradation of 3-PBA, the main metabolite of fenpropathrin, were also investigated in three soils. Soil microorganisms were confirmed as the main factor that is responsible for enantioselective degradation of fenpropathrin enantiomers in soil. Such results provide a new approach for fenpropathrin enantiomer separation and contribute to a comprehensive risk assessment of fenpropathrin at the enantiomer level.
The separation of benoxacor enantiomers on six commercial chiral columns was investigated by high-performance liquid chromatography (HPLC) under normal-phase and reversed-phase conditions. The mobile phases included hexane/ethanol, hexane/isopropanol, acetonitrile/water, and methanol/water. The effects of the chiral stationary phases (CSPs), temperature, and mobile phase composition and ratio on the separation of benoxacor enantiomers were examined. Under normal-phase conditions, the two benoxacor enantiomers were completely separated on Chiralpak AD, Chiralpak IC, Lux Cellulose-1, and Lux Cellulose-3 columns and partially separated on a Lux Cellulose-2 column. Under reversed-phase conditions, benoxacor enantiomers were completely separated on a Lux Cellulose-3 column and partially separated on Chiralpak IC and Lux Cellulose-1 columns. Normal-phase HPLC performed better than reversed-phase HPLC for the separation of benoxacor enantiomers. As the column temperature increased from 10 °C to 4 °C, the enthalpy (ΔH) and entropy (ΔS) results indicated that the resolution was strongly affected by the temperature and that the lowest temperature did not always produce the best resolution. An optimized separation method on the Lux Cellulose-3 column was used to investigate the stability of benoxacor enantiomers in solvents and the degradation of benoxacor enantiomers in three types of horticultural soil. Benoxacor enantiomers were stable, and degradation or racemization were not observed in methanol, ethanol, isopropanol, acetonitrile, hexane, or water (pH = 4.0, 7.0, and 9.0). In three horticultural soils, the degradation rate of S-benoxacor was faster than that of R-benoxacor, resulting in soil enrichment with R-benoxacor. The results of this study will help to improve the risk assessment of enantiomer levels of benoxacor in the environment.Keywords:benoxacor;chiral separation;enantiomers;enantioselectivity;soil degradation
By developing a novel chiral column, we integrate open tubular capillary electrochromatography into sheathless mass spectrometry (MS) for efficient analysis of underivatized amino acid enantiomers. The chiral column is easily fabricated by modifying the inner surface of a capillary with a three-dimensional porous layer (PL, thickness ∼ 90 nm, pore size ∼ 30 nm) and gold nanoparticles and by introducing a chiral selector, thiol β-cyclodextrin (SH-β-CD), onto the modified surface via Au–S bonds. This approach greatly enhances the specific surface area and thus the ratio of the stationary phase to mobile phase and interaction between the stationary phase and analytes. The proposed PLOT@Au@CD column is coupled to the sheathless CE-ESI-MS system for chiral analysis of amino acid enantiomers. No derivatization of amino acids is required for chiral analysis, and baseline separation of a total of 15 pairs of amino acid enantiomers is achieved within 17 min with high column efficiencies of 5.60 × 104 to 1.82 × 106 N/m, high resolutions of 1.51–10.0, and low limits of detection between 0.02 and 0.09 μg/mL. The separation efficiency and MS intensity are only slightly decreased over 60 runs or after usage for 15 days, showing excellent repeatability and stability of the PLOT@Au@CD column. The proposed method is successfully applied to the determination of amino acid enantiomers in vinegar samples with satisfactory accuracy. Our study provides a new approach for developing a chiral stationary phase in the chromatographic separation technique, which can be easily coupled to sensitive MS detection, thus it would be of value for various applications in the fields of chiral analysis.
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