Deep Eutectic Solvent-Based Headspace Single-Drop Microextraction of Polycyclic Aromatic Hydrocarbons in Aqueous Samples

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 compounds 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 microextraction, 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 thermal 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. 1 and see Supplementary materials Fig. S1). injected into the GC system for analysis. Moreover, chemometrics and multivariate statistics were uti- 2.4. The accomplishment of the experiment lized to optimize the main independent variables that might in- fluence the procedure efficiency. Finally, the feasibility study was Ten milliliters of the working standard or sample solutions were evaluated to analyze PAHs under the optimal extraction procedure transferred into 15-mL vials containing a small magnetic stir bar in different aqueous samples. (1.0 × 0.5 cm). Next, the optimum ionic strength and pH of the solutions were adjusted. The HS-SDME was accomplished by simply 2. Experimental hanging a microdroplet of the DES (15 μL) as the extracting media in the headspace of the mentioned samples using the modified mi- 2.1. Chemicals and materials crosyringe (see Supplementary materials, Fig. S2). The microdroplet was drawn back into the syringe and transferred into a micro vial EPA standard mixture of 16 priority PAHs was obtained containing 10 μL n-hexane and 10 μL water after extraction in op- from Sigma-Aldrich (USA) as follows: acenaphthene (Ace), timum conditions due to the incompatibility of DESs with the GC benzo[ k ]fluoranthene (BkF), anthracene (Ant), benz[ a ]anthracene system [13] . The mixture was shaken for 3.0 min to back-extract (BaA), acenaphthylene (Acy), benzo[ b ]fluoranthene (BbF), chrysene the analytes from the collected phase into n-hexane. Finally, 2.0 μL (Chr), benzo[ a ]pyrene (BaP), benzo[ ghi ]perylene (BgP), fluoran- of the organic layer was injected into the GC–MS system. thene (Flt), dibenz[ a,h ]anthracene (DBA), indeno[1,2,3- cd ]pyrene (Ind), fluorene (Flu), naphthalene (Nap), pyrene (Pyr), phenan- 3. Results and discussion threne (Phe), and Benzo[ b ]chrysene (IS). All other chemicals with high purity grades were obtained from Merck (Darmstadt, 3.1. Optimization of Des-Hs-Sdme procedure Germany). The mixture stock standard solution of the PAHs was prepared in acetonitrile at 100 μg mL −1 concentration of each To obtain the maximum extraction efficiency, the optimization analyte. This solution was further diluted to 0.5–10 μg L −1 to ob- of DES-HS-SDME procedure was studied in two steps, followed by tain a working solution, which was stored at 4 °C and used daily evaluating independent factors including the type of DES system, in proper concentrations or directly. In addition, ultrapure water extraction time, ionic strength, sample temperature and stirring

2 A. Mehravar, A. Feizbakhsh, A.H.M. Saraﬁ et al. Journal of Chromatography A 1632 (2020) 461618

Fig 1. FTIR diagram of a) Oxalic acid, b) Choline chloride, c) ChCl-Ox DES, 1:2.

rate. A classical univariate method and design of the experiment code, low, center and high levels of each variable, and the matrix were utilized for estimating the optimal type of DES and other is randomly generated for 27 experiments. The ANOVA and regres- main factors, respectively. sion were used to establish a proper model and choose statistically First, different DES systems such as ChCl-urea (DES1), ChCl- important factors. The results confirmed that the developed model glycerol (DES2) and ChCl-Ox (DES3) were investigated under three was significant due to the p < 0.05 and F-value of 13.78. The val- different mole ratios as extracting media. The selected mole ratio ues of the lack of fit ( p > 0.06) were considered insignificant (see was 1:2 for DES1, DES2 and DES3, as well as1:3 and 1:4 for ChCl- Supplementary materials, Table S4). In the present study, a second- Ox (DES4) and ChCl-Ox (DES5), respectively. Based on the results, order polynomial model ( Eq. (1) ) was obtained by using stepwise the mean values for the five DESs were different (see Supplemen- multiple linear regression and ANOVA methods. This model rep- tary materials, Fig. S3). A one-way ANOVA was used to evaluate the resents the relationship between the dependent and independent effect of the type of DESs on the extraction efficiency of the pro- variables. posed procedure for five different kinds of DESs. The type of DESs had a significant effect on extraction efficiency at p < 0.05 level for = . − . + . + . − . − . 2 = = Y 1 0167 0 2733A 0 0442B 0 0325C 0 1317D 0 1867A the five conditions (F (4, 25) 32.01 and p 0.001, see Supple- mentary materials, Table S2). The post-hoc comparisons through (1) the Tukey HSD test indicated that the mean score of the DES3 ( M = 30.233, SD = 0.726) was significantly higher than that of the The fitness of the model was confirmed by the statisti- other DESs (see Supplementary materials, Fig. S4). In general, these cal parameters (R 2 = 95.14%, adjusted-R 2 = 88.31%, and predicted- results suggested that the DES3 affected the dependent variable. R 2 = 72.51%). In addition, the coefficient of determination (R 2 ) More precisely, the results indicated that the extraction efficiency demonstrated that 95.14% of the variability of the response was was significantly increased when the DES3 was applied as an ac- covered by the proposed model. The predicted-R 2 explained that cepting phase. 72.51% of new data were predicted by the model. Further, a reason- Then, the sample temperature, ionic strength, extraction time able agreement was observed between predicted- and adjusted- and stirring rate as effective factors on the proposed procedure R 2 values due to the slight difference between these two val- performance were statistically assessed through a Box-Behnken de- ues. Therefore, the results confirmed the validity of the proposed sign. Table S3 demonstrates the details of the design including model.

3 A. Mehravar, A. Feizbakhsh, A.H.M. Saraﬁ et al. Journal of Chromatography A 1632 (2020) 461618

Table 1 Quality analytical data of the proposed method under optimum conditions using the GC–MS.

a b −1 c 2 d e −1 f −1 g Compound t r (min) LR (μg L ) R F exp LOD (μg L ) LOQ (μg L ) Intra-day precision (RSD%, n = 10) Inter-day precision (RSD%, n = 3) EF

Nap 13.45 0.02–50 0.9995 3.45 0.009 0.024 5.5 8.4 286 Acy 17.41 0.02–30 0.9998 3.12 0.007 0.022 6.1 11.3 275 Ace 17.89 0.02–50 0.9992 2.18 0.009 0.025 3.9 8.8 315 Flu 19.41 0.02–50 0.9989 1.85 0.008 0.020 7.2 9.5 320 Ant 22.61 0.01–50 0.9993 3.42 0.003 0.009 5.3 6.8 395 Phe 22.84 0.01–50 0.9996 1.99 0.004 0.013 5.6 7.3 357 Flt 27.26 0.02–50 0.9994 2.98 0.006 0.021 4.9 6.2 280 Pyr 28.28 0.02–45 0.9991 2.78 0.005 0.018 5.8 7.0 275 BaA 33.61 0.02–15 0.9993 2.09 0.008 0.023 6.5 8.3 278 Chr 33.87 0.01–5 0.9997 1.92 0.005 0.012 6.9 8.5 335 BbF 39.38 0.02–5 0.9998 3.12 0.007 0.024 4.7 9.8 317 BkF 39.58 0.02–15 0.9996 2.26 0.009 0.022 5.2 7.9 315 BaP 41.84 0.02–5 0.9994 1.86 0.009 0.021 5.8 7.2 260 Ind 46.97 0.02–15 0.9999 3.10 0.007 0.025 6.0 8.6 245 DBA 47.14 0.03–5 0.9998 2.82 0.009 0.029 5.9 10.7 215 BgP 48.34 0.05–5 0.9995 2.43 0.012 0.049 6.3 7.9 250

a t r is retention time.

b LR is linear range.

c R 2 is the determination coeﬃcient. d = = = Fexp is the ratio of residual variance to squared pure error, critical F(0.05, 42, 30) 1. 79, is the critical value of F with (I-3) 42 and (I-L) 30 degrees of freedom at 95% conﬁdence level, where I is the number of calibration samples (45) and L the number of concentration levels (15).

e LOD is limit of detection.

f LOQ is limit of quantiﬁcation.

g EF is enrichment factor.

The effect of the independent variables on the analytical sig- The statistical validation of a calibration model was assessed nal and their possible interactions were graphically considered by through investigating the relationship between the concentration the three-dimensional (3D) two-factor response surface plots of of the analytes at fifteen levels (0.005–70.0 μg L −1 ) in the stan- the model (see Supplementary materials, Fig. S5). To obtain the dard samples and corresponding peak area. Each concentration optimum values of the variables, terms ∂ Y/ ∂ A, ∂ Y/ ∂ B, ∂ Y/ ∂ C and was analyzed in triplicate under the optimized pretreatment con- ∂ Y/ ∂ D were calculated, and each one was equated to zero. The ditions of the sample. The coefficient of determination (R 2 ) was resulting equations were simultaneously solved to achieve micro- applied to confirm the fitness of model equations for regression extraction and determination of the target analytes indicating the lines ( Table 1 ). The values of the R 2 illuminated a good rela- maximum analytical signal. . The mass transfer into the aqueous tionship between the variables and confirmed that the calculated sample and the diffusion of analytes into the extractant were ef- model could explain more than 99.91% of the results for the ana- ficiently achieved by increasing the agitation and temperature of lytes ( Table 1 ). Additionally, the linearity is considered as an im- the sample solution. Hence, the extraction efficiency was improved portant quality in developing an analytical method, which is in- while the extraction time was decreased (see Supplementary ma- correctly assessed by measuring the R 2 or correlation coefficient terials, Fig. S5). Accordingly, a stirring rate of 20 0 0 rpm was chosen (R) of a calibration graph [18,19] . The correlation coefficient eval- for 10 min. Furthermore, the sample temperature was considered uates the relationship between two random variables and it has as another important variable which affected the kinetic and ther- no meaning in calibration [20] . Moreover, IUPAC has discouraged modynamic parameters of the extraction process leading to a faster the correlation coefficient as an indicator of linearity in the re- partition equilibrium. Based on the results, the optimum tempera- lationship between concentration and signal [17] . In the current ture for obtaining the highest extraction yield was 50 ᵒ C (see Sup- study, the ANOVA was used to determine linearity. Thus, the ratio plementary materials, Fig. S5). The higher temperature decreased of the lack-of-fit variance to the squared pure error was estimated the extraction yield, which might be related to the fact that wa- through statistic Fisher variance (F-test). The results indicated that ter molecules compete with the analytes in transferring from the the ratio Fcritical /Fexperimental value was higher than 1.0. The findings aqueous sample into the headspace leading to a decrease in the demonstrated the significance of linear function models by consid- extraction recovery. An increase in ionic strength led to a reduc- ering the appropriate R 2 for the analytes and results of the F-test tion in the solubility of PAHs in the aqueous phase, while higher ( Table 1 ). In addition, the analytical sensitivity was associated with ionic strength might cause an increase in density and viscosity of the calibration graph, which was calculated using the valuation of the sample solution and also a reduction in extraction yield (see the limits of detection and quantification [21] . Based on the re- Supplementary materials, Fig. S5). Therefore, an ionic strength pre- sults, these two limits ranged 0.003–0.012 and 0.012–0.049 μg L −1 pared using a 10% (w/v) NaCl aqueous sample solution was se- for the PAHs, respectively. lected. The precision of the method was evaluated through the intra- and inter-day precision, represented by the relative standard de- viation. The intra-day precision was evaluated by determining 10 3.2. Validation of the method analytical parameters replicates on the same day at three different concentrations, while the inter-day precision was assessed via delineating 30 tests (i.e., The aim of the present study was to develop DES-HS-SDME as a three concentrations and three examinations per day for three new analytical procedure for the reliable analysis of PAHs in aque- days). Table 1 illustrates the related data. Based on the results, the ous samples. Hence, the proposed method was validated based on intra- and inter-day precision values were in the range of 3.9–7.2 the International Union of Pure and Applied Chemistry (IUPAC) and and 6.2–11.3%, respectively. International Conference on Harmonization (ICH) guidance docu- To evaluate the feasibility and accuracy of the proposed DES- ments in order to ensure reliability, traceability or comparability SDME, four water samples collected from different locations were [16,17] .

4 A. Mehravar, A. Feizbakhsh, A.H.M. Sarafi et al. Journal of Chromatography A 1632 (2020) 461618 spiked at low, medium and high concentration levels of the ana- References lytes, and then were measured under optimal conditions. The per- centage relative recoveries (RR%) to the spiked samples were eval- [1] L. Wu, R. Sun, Y. Li, C. Sun, Sample preparation and analytical methods for polycyclic aromatic hydrocarbons in sediment, Trends Anal. Chem. 24 (2019) uated by comparative analysis (t-test) at 95% level of confidence e0 0 074, doi: 10.1016/j.teac.2019.e0 0 074 . [22,23] . Finally, the results revealed satisfactory RR% ranges for the [2] M.A . Jeannot, A . Przyjazny, J.M. Kokosa, Single drop microextraction –develop- PAHs, and the accuracy of the method was confirmed (see Supple- ment, applications, and future trends, J. Chromatogr. A 1217 (2010) 2326–2336,

doi:10.1016/j.chroma.2009.10.089. mentary materials, Table S5). Figure S6 represents the examples of [3] M.A. Jeannot, F.F. Cantwell, Solvent microextraction into a single drop, Anal. chromatograms of the blank and fortiﬁed wastewater sample. Chem. 13 (1996) 2236–2240, doi: 10.1021/ac960042z . The analytical features of the present technique were compared [4] Y. He, H.K. Lee, Liquid-Phase Microextraction in a Single Drop of Organic Sol- with those of other microextraction techniques such as different vent by Using a Conventional Microsyringe, Anal. Chem 22 (1997) 4634–4640, doi: 10.1021/ac970242q . modalities of the SDME method. Based on the results, the proposed [5] F. Pena-Pereira, I. Lavilla, C. Bendicho, Single-drop microextraction and re- approach which could produce LODs and EFs was superior or com- lated techniques, in: M. Valcárcel, S. Cárdenas, R. Lucena (Eds.), Analyti- parable to other procedures (see Supplementary materials, compar- cal Microextraction Techniques, Bentham Science Publisher, 2017, 327–379. 10.2174/97816810837971170101. ative study section and Table S6). Further, the proposed method [6] J. Wei, X. Zhang, Z. Hou, X. Lue, High-quality total RNA extraction from Mag- compared to other methods was a safer, more cost-effective and nolia sieboldii K. Koch seeds: a comparative evaluation, J. For. Res. 30 (2019) eco-friendly approach. 371–379, doi: 10.1007/s11676- 018- 0615- 8 . [7] A. SarafrazYazdi, F. Mofazzeli, Z. Es’haghi, Determination of 3-nitroaniline in water samples by directly suspended droplet three-phase liquid-phase mi- 4. Conclusions croextraction using 18-crown-6 ether and high-performance liquid, J. Chro- matogr.A 1216 (2009) 5086–5091, doi: 10.1016/j.chroma.2009.04.090 . [8] M. Havlikova, R. Cabala, V. Pacakova, M. Bursova, Z. Bosakova, Critical eval-

An improved technique, DES-based HS-SDME, was developed to uation of microextraction pretreatment techniques - Part 1: single drop and determine PAHs in aqueous samples. In this method, sample clean- sorbent-based techniques, J. Sep. Sci. 42 (2019) 273–284, doi: 10.1002/jssc. up and analyte preconcentration were simultaneously achieved in 201800902 .

[9] M.R. AfsharMogaddam, A. Mohebbi, A. Pazhohan, F. Khodadadeian, M.A. Fara- a single step. Some physical and chemical properties of DESs in- jzadeh, Headspace mode of liquid phase microextraction: a review, Trends cluding more biodegradability, less toxicity, relatively large viscos- Anal. Chem 110 (2019) 8–14, doi: 10.1016/j.trac.2018.10.021 . ity, negligible vapor pressure, high thermal stability and excel- [10] O. Nacham, T.D. Ho, J.L. Anderson, G.K. Webster, Use of ionic liquids as lent solubility made them more convenient extractant compared to headspace gas chromatography diluents for the analysis of residual solvents in pharmaceuticals, J. Pharm. Biomed. Anal. 145 (2017) 879–886, doi: 10.1016/j. conventional organic solvents and imidazolium-based ILs. The bell- jpba.2017.05.033 . shaped extraction tube in the proposed method led to the high [11] R. Toniolo, N. Dossi, R. Bortolomeazzi, G. Bonazza, S. Daniele, Volatile alde- stability of the microdroplet. Hence, the extraction process could hydes sensing in headspace using a room temperature ionic liquid-modiﬁed electrochemical microprobe, Talanta 197 (2019) 522–529, doi: 10.1016/j.talanta. be performed in higher temperatures and faster stirring rates. Sub- 2019.01.049 . sequently, the extraction eﬃciency of the method was improved, [12] A . Shishov, A . Bulatov, M. Locatelli, S. Carradori, V. Andruch, Application of and the extraction time was decreased. Satisfactory extraction ef- deep eutectic solvents in analytical chemistry. A review, J. Microchem. 135 (2017) 33–38, doi: 10.1016/j.microc.2017.07.015 .

ﬁciency and sensitivity were obtained through statistical optimiza- [13] P.M. Godwin, Y. Pan, H. Xiao, M.T. Afzal, Progress in the preparation and ap- tion of the important experimental variables. The method was sim- plication of modiﬁed biochar for improving heavy metal ion removal from ple, time-saving and eco-friendly chemical consumption. Finally, wastewater, J. Bioresour. Bioprod. 4 (2019) 31–42, doi: 10.21967/jbb.v4i1.180 . [14] P. Mako s,´ E. Słupek, J. G ebicki,˛ Hydrophobic deep eutectic solvents in microex- the improved DES-based HS-SDME was successfully used to extract traction techniques: a review, J. Microchem 152 (2020) 104–384, doi: 10.1016/j. PAHs in different water samples. microc.2019.104384 . [15] Z. Triaux, H. Petitjean, E. Marchioni, M. Boltoeva, C. Marcic, Deep eutectic

solvent-based headspace single-drop microextraction for the quantiﬁcation Declaration of competing interest of terpenes in spices, Anal Bioanal Chem 412 (2020) 933–948, doi: 10.1007/ s00216- 019- 02317- 9 . The author(s) declare that they have no competing interests. [16] S.M. Youseﬁ, F. Shemirani, S.A. Ghorbanian, Enhanced headspace single drop microextraction method using deep eutectic solvent based magnetic bucky gels: application to the determination of volatile aromatic hydrocarbons in CRediT authorship contribution statement water and urine samples, J. Sep. Sci. 41 (2018) 966–974, doi: 10.1002/jssc. 201700807 .

Amir Mehravar: Investigation, Conceptualization, Method- [17] ICH Harmonized Tripartite Guideline, Validation of Analytical Procedures: text and Methodology Q2 (R1)International Conference of Harmonization of Tech- ology, Writing - original draft, Formal analysis, Resources. nical Requirements for Registration of Pharmaceuticals for Human Use, 2005 . Alireza Feizbakhsh: Supervision, Project administration. [18] IUPAC, Harmonized guidelines for single-laboratory validation of method of Amir Hosein Mohsen Saraﬁ: Supervision. Elaheh Konoz: Writing analyses (IUPAC technical report), Pure Apple. Chem 74 (2002) 835, doi: 10. 1351/pac200274050835 .

- review & editing. Hakim Faraji: Conceptualization, Data cura- [19] A.C. Olivieri, Practical guidelines for reporting results in single- and multi- tion, Methodology, Project administration, Software, Validation, component analytical calibration: a tutorial, Anal. Chim. Acta 868 (2015) 10– Visualization, Writing - review & editing. 22, doi: 10.1016/j.aca.2015.01.017 . [20] Analytical Methods Committee, Is my calibration linear? Analyst 119 (1994) 2363–2366, doi: 10.1039/an9941902363 . Acknowledgement [21] K. Danzer, L.A. Currie, Guidelines for calibration in analytical chemistry. Part 1. Fundamentals and single component calibration, Pure Appl. Chem. 70 (1998)

993–1014, doi:10.1351/pac199870040993. This study was supported by grants from the Central Tehran [22] H. Faraji, M. Helalizadeh, Lead quantiﬁcation in urine samples of athletes by Branch, Islamic Azad University. coupling DLLME with UV-vis spectrophotometry, Biol. Trace Elem. Res 176 (2017) 258–269, doi: 10.1007/s12011- 016- 0844- 7 .

Supplementary materials [23] M. Shahbodaghi, H. Faraji, H. Shahbaazi, M. Shabani, Sustainable and green microextraction of organophosphorus ﬂame retardants by a novel phosphonium- based deep eutectic solvent, J. Sep. Sci. 43 (2020) 452–461, doi: 10.1002/jssc. Supplementary material associated with this article can be 201900504 . found, in the online version, at doi: 10.1016/j.chroma.2020.461618 .

5 本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP 图书馆。图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页文献云下载图书馆入口外文数据库大全疑难文献辅助工具