Journal of Chromatography A 1632 (2020) 461618 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Deep eutectic solvent-based headspace single-drop microextraction of polycyclic aromatic hydrocarbons in aqueous samples ∗ Amir Mehravar a, Alireza Feizbakhsh a, , Amir Hosein Mohsen Sarafi a, Elaheh Konoz a, ∗ Hakim Faraji b, a Department of Chemistry, Central Tehran Branch, Islamic Azad University, Tehran, Iran b Department of Chemistry, Varamin-Pishva Branch, Islamic Azad University, Varamin 338177489, Iran a r t i c l e i n f o a b s t r a c t Article history: An improved deep eutectic solvent (DES)-based headspace single-drop microextraction procedure has Received 29 September 2020 been developed as a green procedure for gas chromatography-mass spectrometric analysis of polycyclic Revised 8 October 2020 aromatic hydrocarbons (PAHs) in aqueous samples. The stability of the micro-drop was significantly im- Accepted 9 October 2020 proved using a DES as an extraction phase and a bell-shaped tube as a supporter. These strategies helped Available online 13 October 2020 to perform the extraction process in higher temperatures and stirring rates. Finally, the back-extraction of Keywords: the analytes into a proper solvent that is compatible with the chromatography system was applied. The Green analytical chemistry efficacy of the independent variables on the extraction efficiency was evaluated via chemometric meth- Deep eutectic solvents ods in two steps. The best result was obtained with choline chloride-oxalic acid at the molar ratio of Headspace single-drop microextraction 1:2, a stirring speed of 20 0 0 rpm for 10 min as well as a sample temperature of 50 °C and with ionic Aqueous samples strength prepared by using a 10% (w/v) NaCl. The method indicated a good linearity for the analytes Polycyclic aromatic hydrocarbons analysis − (R 2≥0.9989). Under optimal conditions, the analytical signal was linear in the range of 0.01–50 μg L 1. Limit of detection (LOD) and limit of quantification (LOQ) were evaluated at the concentration levels of 0.003–0.012 and 0.009–0.049 μg L −1, respectively. Intraday and interday precision for all targeted com- pounds was less than 7.2% and 11.3%, respectively. Consequently, the proposed procedure was efficiently applied to extract and analyze the 16 target compounds in real aqueous samples representing satisfactory recoveries (94.40–105.98%). © 2020 Elsevier B.V. All rights reserved. 1. Introduction uous flow SDME, drop-to-drop SDME, continuous-flow microex- traction, solidification of floating organic drop microextraction and The sample preparation including pre-treatment and pre- directly suspended droplet (DSD)-SDME. In addition, the liquid- concentration of analytes within complex matrices remains a bot- liquid-liquid (LLL)-SDME, headspace (HS)-SDME as well as a com- tleneck in precise analytical procedures, mainly for determining bination of LLL and DSD are considered as examples of the second the compounds at trace or ultra-trace levels. Liquid-liquid extrac- mode [2 , 5 , 6] . tion (LLE) and solid-phase extraction (SPE) as two classical tech- The HS-SDME is regarded as a mode of SDME and is appropri- niques frequently involve tedious and labor-intensive methods and ate for extraction of low molecular weight compounds, which can need large amounts of toxic solvents [1] . be polar or nonpolar, volatile or semi-volatile and from complex Liquid-phase microextraction techniques are known as mi- sample matrices into a single microdroplet of an organic solvent croscale of the classical LLE, introduced in the mid-to-late 90 s suspended on the tip of a microsyringe exposed to the headspace [2] . These methods have been proposed to overcome the short- of the evaluated sample in a vial. Then, the microdroplet is pulled comings of traditional sample preparation systems. Therefore, the back into the syringe and introduced into the analytical system for basic concept of single-drop microextraction (SDME) was first sug- further analysis. The HS-SDME is technically straightforward, cost- gested by Jeannot and Cantwell [3] and He and Lee [4] . Some and time-effective, environmentally friendly and without carry- examples of two-phase SDME include direct immersion, contin- over problem as well as can simply be automated [7] . Despite the above-mentioned advantages, this technique suffers from volatil- ity, lack of drop stability as well as limitation of extraction drop ∗ Corresponding authors. surface area and volume [8] . Accordingly, choosing an extraction E-mail addresses: [email protected] (A. Feizbakhsh), [email protected] phase with capabilities such as dissolving the target analytes to (H. Faraji). https://doi.org/10.1016/j.chroma.2020.461618 0021-9673/© 2020 Elsevier B.V. All rights reserved. A. Mehravar, A. Feizbakhsh, A.H.M. Sarafi et al. Journal of Chromatography A 1632 (2020) 461618 improve the extraction efficiency, having a high-boiling point with was created from a system related to Milli-Q water purification low vapor pressure to reduce evaporation, owning low level of tox- (Millipore, Bedford, MA, USA). icity and high viscosity to stabilize micro-drop has always been fa- Tap water samples were taken from a water tap in our labora- vored by researchers. Most solvents used as the extraction phase tory, and the well water samples were sourced from a well near in HS-SDME are not able to provide the mentioned requirements. a gas station (Varamin, Iran). Further, river water and wastewater Compared to traditional solvents, the proposed ionic liquids samples were collected from the Jajrood River (Tehran, Iran) and (ILs) have revealed promising results as the matrix media for the industrial zone (Charmshahr, Varamin), respectively. All samples HS technique due to their inherent properties [9–11] . Furthermore, were stored at a temperature of 4 °C after collection. Tap water the deep eutectic solvents (DESs) as the alternative to classical ILs was used as received without any treatment, while other samples have been recently introduced in the sample pretreatment meth- were filtrated before analysis. ods. These solvents have similar properties to ILs (e.g. high ther- mal stability, excellent solubility and negligible vapor pressure). 2.2. Instrumentations Moreover, they have more advantages such as cheapness and ease of synthesis, more biodegradability and less toxicity [11–13] . The Chromatographic analysis was conducted from an Agilent majority of DESs synthesized and reported so far are hydrophilic. 6890 N gas chromatography system equipped with a mass spec- Thus, their application for separation processes in aqueous matri- trometer (MS) in the mode of selected ion monitoring (see Supple- ces has been limited. Hence, the DESs as the extraction medium mentary materials, Table S1). The separation was conducted on an can be one of the most appropriate candidates to develop the HS HP-5 MS (30 m × 0.25 mm × 0.25 μm) capillary column (Agilent, techniques for analysis of volatiles and semi volatiles trace com- USA). Two microliters of the final solution was introduced into the pounds in aqueous samples. However, the relatively low volatil- injection port (320 °C) under splitless mode. The oven temperature ity and high viscosity of most DESs can be a double-edged sword program included 50 °C for 2 min, increased to 190 °C at 10 °C when they are applied as an extraction phase in the microextrac- min −1 and then ramped at a rate of 5 °C min −1 to 280 °C. Finally, tion techniques combined with chromatography systems, especially the temperature was increased at the heating rate of 5 °C min −1 gas chromatography (GC) systems. These properties prevent the up to 310 °C. The detector temperature was set at 310 °C. whole evaporation of DESs in the GC injection port leading to liner and column contamination as well as instability in the baseline 2.3. Preparation of deep eutectic solvents and carrier gas flow rate [13] . To the best of our knowledge, ev- idence on the application of DESs as an extractant in HS-SDME is Choline chloride (ChCl) as the hydrogen-bond acceptor and ox- rare and still in its infancy [14,15] . The aim of the present study alic acid (OX), urea and glycerol as the three main groups of was to develop an HS-SDME through DES combined with GC–MS hydrogen-bond donors were evaluated to prepare DES mixtures. in order to extract, separate and determine polycyclic aromatic hy- Early experiments have demonstrated that the ChCl-OX mixtures drocarbons (PAHs) in aqueous samples. Various strategies includ- have more ability to extract PAHs from the headspace of aque- ing hardware and software tools were used to improve the short- ous matrices compared to other eutectic systems such as ChCl- comings of conventional HS-SDME and to take an effective step for urea (DES1) and ChCl-glycerol (DES2). Thus, in order to select the bringing the technique closer to green analytical chemistry. In this best DES system to extract the goal analytes from the samples, the context, the DESs were applied as a green medium and a home- ChCl with OX in various molar ratios [1:2 (DES3), 1:3 (DES4) and made bell-shaped extraction tube was attached to the tip of the 1:4 (DES5)] was synthesized by mixing them in a screw-capped syringe needle. In addition, to address the above-mentioned chal- vial under sonication at 75 °C for 3 min until a homogeneous and lenges in the combination of DESs and GC, following extraction un- clear liquid was obtained. The chemical structures of the synthe- der optimum conditions, back-extraction of the analytes from the sized DESs were characterized and confirmed by analyzing their collected DES into n-hexane was performed. The latter was then FT-IR spectra ( Fig.