Abstract
An emulsification liquid–liquid microextraction (ELLME) method was successfully developed using phenolic-based deep eutectic solvent (DES) as an extraction solvent for the determination of phenoxy acid herbicides, 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) in environmental water samples. Five different phenolics-based DESs were successfully synthesized by using phenol (DES 1), 2-chlorophenol (DES 2), 3-chlorophenol (DES 3), 4-chlorophenol (DES 4) and 3,4-dichlorophenol (DES 6) as the hydrogen-bond donor (HBD) and choline chloride as the hydrogen-bond acceptor (HBA). The DESs were mixed at 1 : 2 ratio. A homogeneous solution (clear solution) was observed upon the completion of successful synthesis. The synthesized DESs were characterized by using Fourier transform infrared and nuclear magnetic resonance (NMR). Under optimum ELLME conditions (50 µl of DES 2 as extraction solvent; 100 µl of THF as emulsifier solvent; pH 2; extraction time 5 min), enrichment factor obtained for dicamba and MCPA were 43.1 and 59.7, respectively. The limit of detection and limit of quantification obtained for dicamba were 1.66 and 5.03 µg l−1, respectively, meanwhile for MCPA were 1.69 and 5.12 µg l−1, respectively. The developed ELLME-DES method was applied on paddy field water samples, with extraction recoveries in the range of 79–91% for dicamba and 82–96% for MCPA.
Highlights
Phenoxy acid herbicides are one of the commonly used herbicides to control the growth of broadleaf weeds, especially in crop plantations such as rice, corn, wheat, fruit trees, forestry and in domestic usage [1,2]
Our work provides insight to contribute to the urgent need for green chemistry for phenoxy acid herbicides residues in the paddy field water sample
The nature of deep eutectic solvent (DES) may have a remarkable effect on the successfulness of the synthesis of DESs and the extraction efficiency of the analytes
Summary
Phenoxy acid herbicides are one of the commonly used herbicides to control the growth of broadleaf weeds, especially in crop plantations such as rice, corn, wheat, fruit trees, forestry and in domestic usage [1,2]. Due to the low concentration of phenoxy acid herbicides in environmental water, sample preparation is a crucial step in analytical procedures to achieve a low limit of detection (LOD) and high accuracy. Liquid–liquid extraction (LLE) and solid phase extraction (SPE) are the most commonly used for phenoxy acid herbicide residues analysis [6–9]. SPE is less solvent consumption method compared to LLE but requires cartridge conditioning and elution with organic solvents. Because of these shortcomings, miniaturized LLE named liquid-phase microextraction (LPME) has been developed in the last decades [10–12]. In ELLME, extraction solvent with high solubility and an emulsifier solvent is added to the sample solutions to extract the target analyte. Of the plethora of microextraction techniques, ELLME has shown several benefits including time-saving, lower consumption of organic solvents and higher extraction efficiency [13]
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