Vortex assisted dispersive liquid–liquid microextraction based on low transition temperature mixture solvent for the HPLC determination of pyrethroids in water samples: Experimental study and COSMO-RS

Highlights

• A simple VADLLME for the analysis of pyrethroids in real water samples has been developed.

• A menthol-based LTTM was used as a green extraction solvent.

• COSMO-RS was used to predict the molecular interaction between LTTMs and pyrethroids.

Abstract

A green, simple, and effective vortex-assisted dispersive liquid–liquid microextraction method that utilizes a menthol-based low transition temperature mixture (menthol-LTTM-VADLLME) was developed to extract and preconcentrate four types of pyrethroids, namely bifenthrin, deltamethrin, fenpropathrin, and permethrin from water samples. In addition, quantum chemical-based conductor-like screening model for realistic solvents (COSMO-RS) software was used to predict the molecular interaction between low transition temperature mixtures (LTTMs) and pyrethroids based on their σ-profile, σ-potentials, and activity coefficient at infinite dilution. High performance liquid chromatography (HPLC) was employed for the further separation of the pyrethroids and their quantification. Several key parameters that affect pyrethroid extraction efficiency are identified as the vortex time, type of LTTM, volume of LTTM, type of dispersive solvent, dispersive solvent volume, type of salt, and amount of salt. The extraction time of 90 s and 150 µL of menthol: sesamol at ratio 1:1 were selected as the best conditions, while ionic strength and type of dispersant solvent were not relevant for the extraction of the target compounds. After optimization, the menthol-LTTM-VADLLME method was found to be able to detect pyrethroids in the range of 0.5–1000.0 μg/L with good linearity (correlation coefficient = 0.9988–0.9995). The method detection limit and quantification limit were found to be in the range of 0.05–0.11 μg/L and 0.18–0.35 μg/L, respectively. The relative standard deviation of inter-day and intra-day precisions were 2.2–5.0% (n = 5) and 1.2–1.9% (n = 7) respectively. The optimized method can successively determine pyrethroids in tap, drinking and river water samples with good recoveries of 73–111%. Hence, this method presents a good approach for determining pyrethroid content in water samples.

Introduction

Pyrethroids are a group of synthetic organic insecticides analogues of pyrethrin which occur in nature such as in chrysanthemum flowers [1]. Pyrethroids are made up of hydrophobic carboxylic esters and they can be categorized into two types: type I which do not contain any cyano substituent) and type II which contain an α-cyano substituent [2]. Pyrethroid pesticides are known as third-generation pesticides [3] and these are generally used in agriculture (crops, forestry, and gardening), for indoor or outdoor pest control (households, farm, warehouses, and public buildings), and in pet shampoo medication formulation (scabies and topical louse treatments) [4], [5]. Pyrethroids are widely used as pesticides due to their high ability to interrupt the brain and nervous system of pest organisms [6]. Furthermore, pyrethroids are only moderately nontoxic to mammals, have selective insecticide activity, effective at low doses, and degrade relatively easily in the environment [7], [8]. However, extensive usage of this pesticide can still cause bioaccumulation in humans, animals, and the environment which can then trigger unfavourable effects [9]. The accumulation of pyrethroids residue in environmental water systems due to movement of pyrethroids by spray drift, surface runoff, and water soil erosion are especially harmful to aquatic systems [9]. Pyrethroids are difficult to eliminate once they accumulate in an organism due to their lipophilic property [10]. The negative effect of pyrethroids on human health becomes apparent after long-term exposure even at low levels. Pyrethroids causes harmful, chronic effects on the immune, nervous, cardiovascular, genetic systems, as well as the male reproductive system [11], [12], [13]. Pyrethroids are also especially poisonous to aquatic organisms [14], [15]. Considering the harmful effect of pyrethroid residue on the environment and general health, it is imperative that a sensitive and effective method for the preconcentration of pyrethroid is developed to facilitate the detection of pyrethroid residue.

Generally, the determination of pyrethroid is problematic because they are present at only trace levels and they are further confounded by interfering compounds in the complex matrix of real samples [16]. Therefore, effective sample preconcentration is an important prerequisite step to isolate the pyrethroids from any interference before analysis [17], [18]. Liquid-liquid extraction (LLE) and solid phase extraction (SPE) are established sample preparation methods that are traditionally used over the years for sample extraction and preconcentration. However, both methods suffer from tedious process steps, long extraction times, and require vast quantities of toxic organic solvents that harm human health and the ecosystem [19], [20]. Up to date, numerous microextraction methods and their applications to various analytical fields have been developed to circumvent the disadvantages of traditional extraction methods namely to improve agreeable with modern analytical instruments, circumvent the use of hazardous chemicals, and allow sampling and sample preparation from a variety of sources [21]. The application of microextraction widely used for detection in environmental [22], [23], [24], [25], [26] and biological [27], [28], [29], [30] samples. The solid-phase microextraction (SPME) method is especially interesting and it is based on the partitioning of the analytes from the sample matrix by a solid fibre media. However, the fibre material is typically costly, brittle, has a limited life-span, and is difficult to dispose [31].

Recently, a liquid phase microextraction (LPME) method was introduced to address the limitations of traditional liquid phase extraction (LLE) methods [32]. LPME are considered environmentally-friendly as the amount of extractant solvent required is low, being only a few microliters compared to the hundreds of millilitres used in conventional LLE [32]. Generally, the LPME method can be further subdivided into three operational modes: drop of solvent [33], [34], hollow fiber-supported solvent [35], [36], and disperser solvent [37]. The disperser solvent operational mode is also known as dispersive liquid–liquid microextraction (DLLME) and it is mainly a ternary solvent system that is formed from the addition of a suitable mixture of an extraction solvent (water immiscible solvent) and the disperser solvent (water miscible solvent) into a sample solution (aqueous solution) [38], [39]. The main advantages of DLLME is that since such as a small amount of extraction solvents is used, the extract is concentrated in a low volume of solvent, and therefore a high enrichment factor can be achieved [38]. On the other hand, the main drawback of DLLME is still the use of toxic and environmentally hazardous extraction solvents [40].

In recent years, the use of green solvents to replace hazardous solvents have become increasingly attractive. Deep eutectic solvents (DESs) and ionic liquids (ILs) are environmental-friendly solvents that are a feasible alternative to conventional organic solvents [41]. However, ILs are disadvantageous compared with DESs especially for large scale applications because they are expensive, have low biodegradability, relatively toxic, and have complex synthesis and purification processes leading to substantial waste generation [42], [43], [44]. The term DES was coined by Abbot and his co-workers in 2003 [45] to describe mixtures with low melting points but do not exhibit any glass transition states [46], [47]. However, many authors have synthesized mixtures with glass transition state but described them to be DES [48], [49], [50]. Therefore in 2012, Francisco and co-workers grouped these solvents as a new and different class on its own, calling them low transition temperature mixtures (LTTMs) [51]. LTTMs are used to describe solvents that have similar properties to DESs but can exhibit a glass transition state [52]. Both DESs and LTTMs are a new and interesting class of solvents that are typically formed by combining hydrogen bond donors (HBAs) with hydrogen bond acceptors (HBAs). The molecules form hydrogen bonds or Van der Waals interactions between them causing the mixture to become a liquid [53], [54], [55]. LTTMs are superior to ILs in the sense that they are less harmful, low cost, and only require simple preparation by mixing naturally occurring compounds without the need for further purification [56]. LTTMs are designer solvents because their properties can be altered by carefully adjusting the ratio of HBDs to HBAs [57]. Generally, LTTMs have low vapour pressure, a broad liquid temperature range, good biodegradability, non-flammability, and an easy preparation process [58], [59]. LTTMs have been applied for use as entrainers [60], [61], extraction solvents [62], [63], [64], [65], [66], [67], [68], [69], for biomass delignification [52], [70], modification of lignin [47], electrodeposition of metal [71], and carbon dioxide capture [56], [72], [73]. However, the application of LTTM in sample preparation studies is still limited [62], [63], [64], [65], [66], [67], [68], [69]. To the best of our knowledge, menthol-based LTTM was not applied to extract pyrethroids. Therefore, the major novelty of this study lies in the exploratory of the performance of menthol-based LTTM as an extractant solvent for VADLLME of pyrethroids.

This study is an extension of our previous study on novel menthol-based LTTMs [65]. The objective of this study is to develop an efficient extraction method of four pyrethroids from water samples using a vortex assisted liquid–liquid microextraction method with menthol-based LTTMs (mixture of menthol and sesamol, ratio 1:1) as the pre-concentrator. Additionally, quantum chemical-based COSMO-RS was used to predict the molecular interaction between LTTMs and pyrethroids at infinite dilution (γ^∞). The important factors affecting the extraction process such as the vortex extraction time, volume of LTTMs, type of dispersive solvent, volume of dispersive solvent, and the type and amount of salt are studied and optimized. Menthol-LTTM-VADLLME is a fast, efficient, and affordable extraction method with a good enrichment factor and adequate accuracy.