Deep eutectic solvent-based emulsification liquid–liquid microextraction for the analysis of phenoxy acid herbicides in paddy field water samples

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.

Retention Modelling of Phenoxy Acid Herbicides in Reversed-Phase HPLC under Gradient Elution

Phenoxy acid herbicides are used worldwide and are potential contaminants of drinking water. Reversed phase high-performance liquid chromatography (RP-HPLC) is commonly used to monitor phenoxy acid herbicides in water samples. RP-HPLC retention of phenoxy acids is affected by both mobile phase composition and pH, but the synergic effect of these two factors, which is also dependent on the structure and pKa of solutes, cannot be easily predicted. In this paper, to support the setup of RP-HPLC analysis of phenoxy acids under application of linear mobile phase gradients we modelled the simultaneous effect of the molecular structure and the elution conditions (pH, initial acetonitrile content in the eluent and gradient slope) on the retention of the solutes. In particular, the chromatographic conditions and the molecular descriptors collected on the analyzed compounds were used to estimate the retention factor k by Partial Least Squares (PLS) regression. Eventually, a variable selection approach, Genetic Algorithms, was used to reduce the model complexity and allow an easier interpretation. The PLS model calibrated on the retention data of 15 solutes and successively tested on three external analytes provided satisfying and reliable results.

Three-dimensional chitosan/graphene oxide aerogel for high-efficiency solid-phase extraction of acidic herbicides in vegetables

A simple, facile method was adopted to synthesize three-dimensional chitosan grafted graphene oxide aerogel modified silica (3D CS/GOA@Sil) as an eco-friendly, sustainable extraction material for the preconcentration of phenoxy acid herbicides.

Determination of Phenoxy Acid Herbicides in Cereals Using High-Performance Liquid Chromatography–Tandem Mass Spectrometry

ABSTRACTAn effective method for determination of multiple residues of phenoxy acid herbicides in cereals was developed. A QuEChERS (quick, easy, cheap, effective, rugged, and safe) technique coupled with high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS) was optimized for the analysis of phenoxy acid herbicides in rice, corn, and wheat. The limits of detection in the experiment were 0.0500 μg/kg for 4-(2,4-dichlorophenoxy)acetic acid, (4-chloro-2-methylphenoxy)acetic acid, (2,4,5-trichlorophenoxy)acetic acid, and 2-(2,4-dichlorophenoxy)propionic acid and 0.300 μg/kg for 4-(2,4-dichlorophenoxy)butyric acid and 3,6-dichloro-2-methoxybenzoic acid. The relative standard deviation of intraday and interday precision for the six phenoxy acid herbicides was less than 6.61%, and accuracy was 96.3 to 107%. Extraction recovery for phenoxy acid herbicides was 73.8 to 115%, with relative standard deviations of less than 12.1% at three spiking levels (1.00, 4.00, and 20.0 μg/kg). These results indicate that QuEChERS sample preparation with HPLC-MS/MS analysis is a rapid, reliable, highly sensitive, and specific tool for the determination of phenoxy acid herbicide residues in cereals.HIGHLIGHTS