Preconcentration using deep eutectic solvents and high performance liquid chromatographic analysis of neonicotinoid insecticides

Abstract

Two different sample preconcentration methods were proposed including (i) in-situ metathesis reaction of deep eutectic solvent (DES) and (ii) dispersive liquid-liquid microextraction (DLLME) using hydrophobic DESs. In the first part, a simple two-step microextraction method followed by high-performance liquid chromatography for rapid determination of neonicotinoid insecticide residues was investigated. Thiamethoxam, clothianidin, imidacloprid, and thiacloprid were chosen as the target analytes. The method used with a cloud-point extraction based on in-situ metathesis reaction of deep eutectic solvents in order to achieve high extraction efficiency. Ultrasonic energy was used to provide mechanical shaking to accelerate the in-situ metathesis reaction. Various experimental parameters affecting the extraction efficiency such as salts addition, types and concentrations of surfactant, concentrations of hydrogen bond donor and hydrogen bond acceptor were investigated and optimized. Four neonicotinoid insecticides were separated within 10 min using monolithic column, with a mobile phase of 26% (v/v) acetonitrile in water, at a flow rate of 0.5 mL min–1, and photodiode array detection at 254 nm. Under the optimum conditions, high enrichment factors (EF) (50-250) and low limits of detection (0.0003-0.001 µg mL-1) were obtained. The proposed method was successfully applied to determine neonicotinoid insecticide residues in surface water, soil and human urine samples and high recoveries were obtained.

In second part, a sensitive hydrophobic DES-based dispersive liquid-liquid microextraction for the determination of neonicotinoid insecticide residues (thiamethoxam, clothianidin, acetamiprid, and thiacloprid) in various samples were established using high-performance liquid chromatography. A hydrophobic deep eutectic solvent was synthesized using decanoic acid as hydrogen bond donor and tetrabutylammonium bromide as hydrogen bond acceptor. The hydrophobic DES extraction phase was rigid after DLLME, being easy to be collected for analysis. Several key parameters were optimized such as salts addition, types of disperser solvent, molar ratio and concentration of hydrophobic DES and extraction times. Four neonicotinoids were separated within 13 min using a Purosphere® STAR RP-18 endcapped column, with a mobile phase of 25 %(v/v) acetonitrile in water at a flow rate of 1 mL min-1, and photo diode array detection at 254 nm. Under the optimum conditions, good precision, high enrichment factor and low limit of detection were obtained. The method is simple, green and practical, and could be applied to the extraction to neonicotinoid insecticide residues in surface water, soil and egg yolk samples and high recoveries within the range of 70-115% were obtained.

-