Abstract
In the present study, the direct enantiomeric separation of hexythiazox enantiomers on Lux cellulose-1, Lux cellulose-2, Lux cellulose-3, Lux cellulose-4, Lux amylose-1 and Chirapak IC chiral columns were carefully investigated by reverse-phase high-performance liquid chromatography (RP-HPLC). Acetonitrile/water and methanol/water were used as mobile phase at a flow rate of 0.8 mL·min−1. The effects of chiral stationary phase, temperature, thermodynamic parameters, mobile phase component and mobile phase ratio on hexythiazox enantiomers separation were fully evaluated. Hexythiazox enantiomers received a baseline separation on the Lux cellulose-3 column with a maximum resolution of Rs = 2.09 (methanol/water) and Rs = 2.74 (acetonitrile/water), respectively. Partial separations were achieved on other five chiral columns. Furthermore, Lux amylose-1 and Chirapak IC had no separation ability for hexythiazox enantiomers when methanol/water was used as mobile phase. Temperature study indicated that the capacity factor (k) and resolution factor (Rs) decreased with column temperature increasing from 10 °C to 40 °C. The enthalpy (ΔH) and entropy (ΔS) involved in hexythiazox separation were also calculated and demonstrated the lower temperature contributed to better separation resolution. Moreover, the residue analytical method for hexythiazox enantiomers in the environment (soil and water) and vegetable (cucumber, cabbage and tomato) were also established with reliable accuracy and precision under reverse-phase HPLC condition. Such results provided a baseline separation method for hexythiazox enantiomers under reverse-phase conditions and contributed to an environmental and health risk assessment of hexythiazox at enantiomer level.
Highlights
Hexythiazox((4RS,5RS)-5-(4-chlorophenyl)-N-cyclohexyl-4-methyl-2-oxothiazolidine-3-carboxa mide, CAS: 78587-05-0, Figure 1) is a non-systemic acaricide widely used to control various mites on vegetables, fruits, cottons, pepper and flowers in agriculture and horticulture [1,2]
When methanol/water was used as mobile phase, hexythiazox enantiomers could be separated on the Lux cellulose-1, Lux cellulose-2, Lux cellulose-3 and Lux cellulose-4 columns, while Lux amylose-1 and Chirapak IC had no separation ability for hexythiazox enantiomers
Partial separation of hexythiazox enantiomers were obtained on Lux cellulose-1, Lux cellulose-2 and Lux cellulose-4 columns with a maximum resolution factor (Rs) of 0.93, 0.81 and 0.73, respectively
Summary
Hexythiazox((4RS,5RS)-5-(4-chlorophenyl)-N-cyclohexyl-4-methyl-2-oxothiazolidine-3-carboxa mide, CAS: 78587-05-0, Figure 1) is a non-systemic acaricide widely used to control various mites on vegetables, fruits, cottons, pepper and flowers in agriculture and horticulture [1,2]. Investigated the chiral separation of hexythiazox enantiomers with amylose-tris-(3,5-dimethylphenylcarbamate) chiral stationary phase under normal-phase HPLC condition and found the best resolution was Rs = 1.75 with an n-hexane/isopropanol ratio of 99.5/0.5. As for reverse-phase HPLC, Tian et al [18] studied the chiral separation of hexythiazox enantiomers on cellulose-tris-(3,5-dimethylphenylcarbamate) and amylase-tris-(3,5-dimethylphenylcarbamate) based two chiral columns and found the best resolution was Rs = 0.96 on amylase-tris-(3,5-dimethylphenylcarbamate) based chiral column with acetonitrile/water ratio of 60/40. The residue analytical method for hexythiazox enantiomers in the environment (soil and water) and vegetable (cucumber, cabbage and tomato) were established with reliable accuracy and precision Such results provided a baseline separation method for hexythiazox enantiomers under reverse-phase HPLC condition and contributed to environmental and health risk assessment of hexythiazox at enantiomer level
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