Pesticides, a type of emerging organic pollutants (EOPs), are ubiquitous in the water environment (Fang, et al., 2019). Since China banned organochlorine pesticides, broad-spectrum organophosphorus pesticides and pyrethroid have been widely used due to their high efficacy and easy degradation (Mao, et al., 2020). They are unknown in number, lack extensive ecotoxicological data, and migrate with water bodies, negatively impacting the ecological environment and human health (Bravo, et al., 2020). As far as existing research data is concerned, these pesticides can cause many problems to the human nervous system, immune system, reproductive system and respiratory system even at low concentrations (Albaseer, 2019). Therefore, the detection of pesticide in environmental water is of great significance to public health and ecosystems (A. J. Li, et al., 2020). The commonly used detection methods are gas chromatography and liquid chromatography (Samsidar, et al., 2018). However, because of the low concentration and complex matrix, a pretreatment step is required to enrich and purify them.
Dispersive liquid-liquid microextraction (DLLME) is an efficient and fast liquid-phase microextraction method proposed by Rezaee (Rezaee, et al., 2006) in 2006. The main improvement work is concentrated on innovating the dispersion method (Psillakis, 2019; Saleh, et al., 2009; Zhong, et al., 2019), updating the phase separation method(Guo, et al., 2016; Ngaosi, et al., 2016; Rezaee, et al., 2012; Ye, et al., 2016; Zhong, et al., 2019), and the usage of low-toxic extractants as much as possible. The ionic liquid (Marcinkowska, et al., 2019) which was used to replace the toxic extractant in DLLME (Montalbán, et al., 2018; Wu, et al., 2013) was found to be harmful to environment recently (Montalbán, et al., 2018). Deep eutectic solvents (DES) proposed by Abbott (Abbott, et al., 2004) in 2003, is a new type of designable green solvents consists of two or more non-toxic hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) which are mechanically mixed in a specific ratio at a certain temperature.
Based on the favorable features of eco-friendliness, degradable, simple synthesis, and adjustable properties, applying DES in DLLME to avoid toxic reagents has become popular research (G. Li, et al., 2019). Many hydrophobic DES are designed to be directly used as extractants to enrich pollutants in water (Ahmadi, et al., 2019; Deng, et al., 2019; Farajzadeh, et al., 2016; Makoś, et al., 2020). Pirsaheb et al. (Pirsaheb, et al., 2018a) hyphenated liquid-phase microextraction and the freezing of DES in detecting pesticides of environmental water, without any disperser solvent. Jouyban et al. (Jouyban, et al., 2020) used DES as extractant to analyze pesticides in milk, and the extraction process can be facilitated by ultrasound or adding organic solvents as dispersants. However, the above methods together with organic solvents and auxiliary instruments make this hyphenated method becomes cumbersome and compromised seriously the eco-friendly. In this paper, a thermo-switchable and environmental friendly DES reported by Longeras et al. (Longeras, et al., 2020) was used to simplify the DLLME steps.
To our best knowledge, this paper applies a thermo-switchable DES to the DLLME for the first time to analysis nine pesticides, which can simplify the dispersion and collection steps of the DLLME simultaneously. During the extraction process, a homogeneous system was formed in ten seconds, and the extractant can aggregate within 1 minute by heating and adding sodium chloride. Nine organophosphorus pesticides and pyrethroids in water samples were successfully analyzed by HPLC with UV detector.