High-fast enantioselective determination of prothioconazole in different matrices by supercritical fluid chromatography and vibrational circular dichroism spectroscopic study

Highlights

• Fast separation and quantification for prothioconazole enantiomers by SFC.

• Absolute configurations of two enantiomers were confirmed through VCD spectroscopy.

• Enantioselective determination of prothioconazole in two matrices.

• Analysis time through SFC was five-fold shorter than traditional HPLC.

Abstract

Herein, we developed a rapid supercritical fluid chromatography (SFC) method for chiral separation and enantioselective determination of prothioconazole in soil and tomatoes. The potential effects of chiral stationary phases, co-solvents, column temperature, and back pressure on enantioseparation of prothioconazole have been studied in detail. Two prothioconazole enantiomers were best separated on cellulose tris(3, 5-dimethylphenylcarbamate)-coated chiral stationary phase with CO₂-2-propanol (80:20, v/v) as the mobile phase, and the run time through SFC (about 4 min) was five-fold shorter than HPLC. Then, through comparing the experimental vibrational circular dichroism spectrum of the later-eluted component with the calculated pattern based on the (R)-configuration, it should be (R)-(-)-prothioconazole. Moreover, the modified QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction and cleanup procedures were applied in enantiomeric analysis of prothioconazole in two matrices. Good linearity (R² ≥ 0.9992) and recoveries (91.84–101.66%, RSD ≤ 3.98%) for two enantiomers were achieved. This proposed method showed good accuracy and precision, and might be suitable for fast enantioselective determination and residual quantitative analysis of prothioconazole in food and environmental samples.

Introduction

Due to high efficiency, broad-spectrum control of major plant pathogens, and relatively low toxicity to non-target organisms, triazole fungicides containing one or several chiral centers have been widely applied in food and environmental fields [1]. As well documented, their enantiomers have exhibited enantioselective absorption, bioactivity, toxicity, and degradation behaviors in chiral environment and have attracted considerable attention in recent years [2], [3], [4], [5], [6]. (R)-Flutriafol was 1.49–6.23 times higher fungicidal activity against five target pathogens (Rhizoctonia solani, Alternaria solani, Pyricularia grisea, Gibberella zeae, and Botrytis cinerea) than (S)-enantiomer, and also exhibited 2.17–3.52 higher acute toxicity towards Eisenia fetida and Scenedesmus obliquus than (S)-enantiomer [4]. (−)−Myclobutanil showed greater toxicity to three non-target organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio) than (+)-myclobutanil, and its degradation in aerobic soils was slower than the latter [5]. Thus, development of fast and high-efficient analysis methods for them has been indispensable to further enantioselective studies on bioactivity, transformation, toxicity, and degradation in multiple matrices.

Prothioconazole, namely, (R, S)− 2-[2-(1-chlorocyclopropyl)− 3-(2-chlorophenyl)− 2-hydroxypropyl]− 1, 2-dihydro-1,2,4-triazole-3-thione (Fig. 1), was developed by Bayer Crop Science and appeared on the market in 2004 [7]. It is a broad-spectrum systemic triazole fungicide with protective, curative, and eradicative activities. Its mode of actions is through inhibiting the C-14α-demethylase enzyme involved in the biosynthesis of fungal sterols [8], [9]. To date, prothioconazole as a racemic mixture has been used in cereal, wheat, soybean, and other economic crops to control powdery mildew, Fusarium head blight, rusts, and leaf spot diseases. There is a concern regarding potential human and wildlife exposure from prothioconazole in the environment. Determination of prothioconazole and its metabolite (prothioconazole-desthio) through HPLC-tandem mass spectrometry has been reported in animal food, peanut, soil, wheat plant, straw, and grain [10], [11]. However, resolution and enantioselective quantification studies for prothioconazole in food and environmental samples have been very limited in the literatures [12], [13], [14]. Wang group developed an UPLC−MS/MS method for enantiomeric determination of prothioconazole and its metabolite enantiomers, in which the retention time of prothioconazole on the Lux Cellulose-3 column was about 20 min through using acetonitrile/water (40:60, v/v) and the recoveries for two enantiomers in five matrices were in the range of 71.8–96.4% with 0.3–11.9% RSDs [13], [14].

Due to better selectivity, higher efficiency, more environmental friendliness, and shorter analysis time, SFC in combination with a broad number of chiral stationary phases (CSPs) has proven to be much superior to conventional HPLC in separation of chiral pharmaceuticals and pesticides, and is outperforming HPLC both in analytical and preparative fields [15], [16], [17]. Herein, a fast SFC analytical method with the QuEChERS (quick, easy, cheap, effective, rugged and safe) extraction and cleanup procedures has been developed for enantiomeric separation and quantification of prothioconazole in two matrices. This QuEChERS method was firstly proposed by Anastassiades M et al. and has widely applied in determination of pesticide residues in multi-matrices in recent years [18], [19]. The effects of chromatographic conditions on enantioseparation of prothioconazole have been investigated in detail. In addition, absolute configurations of two enantiomers have been determined through vibrational circular dichroism (VCD) spectroscopy.