On-site sample pretreatment: Natural deep eutectic solvent-based multiple air-assisted liquid–liquid microextraction

Abstract

Chemical protection is one of the most important methods to control forest pests. Since pesticides used in chemical protection might have significant adverse effects on aquatic organisms, it is essential to monitor and detect trace pesticides in environmental water. In this study, an on-site natural deep eutectic solvent-based multiple air-assisted liquid–liquid microextraction coupled with gas chromatography-electron capture detection was developed for determining triadimefon, bifenthrin, bromopropylate, and permethrin in water samples in the forest. A series of menthol-based deep eutectic solvents were synthesized for the first time to find green and efficient extractants. Moreover, a deep eutectic solvent with a 1:2 molar ratio of DL-menthol to citric acid was selected as the extractant due to its high stability and extraction performance. A portable modular array device based on air-assisted liquid–liquid microextraction was designed and manufactured to enable the simultaneous pretreatment of several samples. Although no electric equipment is required throughout the process, up to six samples were pretreated on-site within 20 min. Moreover, the average sample pretreatment time was less than 3.5 min, and the process was substantially simplified and enhanced. In addition, the parameters affecting the extraction performance were optimized. The extraction recoveries were in the range of 92–95% by using the optimized conditions, and the relative standard deviations of the intra-device, inter-device, intra-day, and inter-day factors were all less than 4.9%. The detection limits of the method ranged from 0.34 to 3.3 µg L−1. Good linearities (R2>0.999) were shown in the linear range of 1.13 to 2500 µg L−1 for the studied pesticides. Moreover, the proposed method was proved to be highly environmentally friendly by the Analytical Eco-Scale and Green Analytical Procedure Index. In summary, the proposed method is green, efficient, and flexible for on-site water sample pretreatment. The fact that tedious operations can be converted into standard operations provides a new perspective for on-site sample processing.