Inside gel electromembrane extraction: A novel green methodology for the extraction of morphine and codeine from human biological fluids

Journal of Pharmaceutical and Biomedical Analysis 184 (2020) 113175

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Inside gel electromembrane extraction: A novel green methodology for the extraction of morphine and codeine from human biological fluids Atyeh Rahimi a , Saeed Nojavan a,∗ , Hadi Tabani b,∗ a b

Department of Analytical Chemistry and Pollutants, Shahid Beheshti University, G. C., Evin, Tehran 1983963113, Iran Department of Environmental Geology, Research Institute of Applied Sciences (ACECR), Shahid Beheshti University, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 17 December 2019 Received in revised form 12 February 2020 Accepted 13 February 2020 Available online 14 February 2020 Keywords: Agarose Codeine Morphine Electroendosmosis flow “Inside” gel-electro-membrane extraction

a b s t r a c t In this work, a new mode of gel-electromembrane extraction (G-EME), called “inside” gel-EME (IG-EME) is proposed for the extraction of morphine and codeine as model basic drugs from complex biological samples. Here, an aqueous media that was captured inside the agarose gel membrane, acted as both gel membrane and the acceptor phase (AP) at the same time. In this regard, the membrane served as the separation filter (membrane) and supported liquid acceptor phase (SLAP) as well. With this new development, unwanted changes of the AP volume during the extraction, which is a common issue in the G-EME (due to electroendosmosis (EEO) phenomenon), was addressed properly. Briefly, the setup involved insertion of negative electrode inside the gel membrane and positive electrode into the donor phase (DP). Following that, the IG-EME was easily performed using optimal conditions (pH of the DP: 6.0; membrane composition (agarose concentration: 1% (w/v) in aqueous media with pH 3.0, and 15 mm thickness); voltage: 25 V; and extraction time: 30 min). After extraction, the agarose gel was withdrawn and centrifuged for 5 min with 12000 rpm, to disrupt its framework to release the “trapped aqueous AP” apart from the gel structure. The separated AP was finally injected into the HPLC-UV for the analysis. The limits of detection (LODs) and recoveries in this proposed method were obtained 1.5 ng mL−1 and 67.7 %–73.8 %, respectively. The system feasibility was examined by the quantification of model drugs in the real plasma and urine samples. © 2020 Elsevier B.V. All rights reserved.

1. Introduction Sample preparation is still a main challenge for many analytical researchers. It is well known that the analysis of drugs in different biological samples can be barely done due to their complexness. The complete elimination of interferences - i.e., small compounds, macromolecules and others which may adversely interact with sensitive detection systems, is one of the most important challenges in sample processing [1–3]. For sure, the high enrichment of target compounds is also helpful for the determination at trace levels [1–5]. Lately, the solvent extraction based on incorporation of a membrane unit between two liquid phases (i.e., donor phase (DP) and acceptor phase (AP)) termed as the membrane extraction, has

∗ Corresponding authors. E-mail addresses: s [email protected] (S. Nojavan), h [email protected] (H. Tabani). https://doi.org/10.1016/j.jpba.2020.113175 0731-7085/© 2020 Elsevier B.V. All rights reserved.

been frequently used among analysts. Pedersen and co-workers proposed a new mode of membrane extraction such as electromembrane extraction (EME), in which electrical field was used as propelling force to transfer ions among different phases (i.e., from DP across membrane to AP) [6]. By using this method, the extraction of ionic analytes in their charged forms occurred in a relatively short time [7–11]. Up to now, several developments and modification upon EME have been reported in the literature [3,12–15]. Mostly, a polypropylene hollow fiber (HF) has been used as the membrane support for the liquid-based filters but also new alternative (more convenient and green) materials were also introduced, in the meantime. Copper ferrocyanide (CFCN) crystals and nafion [12] were applied to enhance the extraction efficiency. In addition, the polar nanostructured support (Tiss® −OH) was applied for the extraction of acidic compounds from human urine samples [13]. Another improvement was using polyvinyldifluoride (PVDF) membrane for the quantification of basic drugs from plasma in very short extraction time (3 min) [14]. Apart from these achievements, Tabani et al. suggested

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recently G-EME based on using agarose gel which was applied for the extraction of several basic drugs with different polarities [15]. The setup provided a green alternative compared to existing traditional EMEs. The further advantage was that no ion-pairing reagents were necessary to use [15–18]. On the other hand, the membrane suffered from unwanted electroendosmosis (EEO) flow phenomenon which occurred during the extraction process. The EEO forces the liquid (with analytes of interest) to pass through the gel membrane interface and the parallel increase and decrease in volume of cathodic and anodic APs, respectively, are the consequences [18]. The electro-migration and EEO in the cathodic membrane appears in the same direction while there is a contrary flow for anodic membrane [18]. Ultimately, the high EEO flow changes the volume of both cathodic and anodic APs and thus dilution of cathodic AP and loss of anodic AP is observed. The second problem leads to the difficulty to extract the anionic compounds. There has been reported only one paper studying different ways to diminish EEO effect in G-EME so far [19]. In this study, various viscous materials such as dextrin, chitosan and xylan with different concentrations i.e., 5 %, 10 % and 15 % were added to agarose gel membrane as additives. The results showed that in presence of 5 % dextrin, extraction efficiency increased while EEO velocity diminished significantly [19]. Thus, in this work, to completely eliminate the problems associated with G-EME, for the first time, the “inside” gel-EME (IG-EME) was developed. Here, we omitted the trend used in classical procedure (i.e., AP represented as individual liquid phase separated from DP via membrane border) in which the AP was “trapped” inside of agarose gel material. Thus, gel acted as both gel membrane and supported liquid acceptor phase (SLAP) at the same time. The effective parameters were investigated and optimized using two basic model drugs with high polarities – i.e., morphine (MOR, log P: 0.8) and codeine (COD, log P: 1.3). At final, the application of this optimized protocol was investigated for the quantification of model drugs in real urine and plasma samples.

2. Experimental 2.1. Reagents and materials The COD and MOR (purity > 99 %) were purchased from Merck (Darmstadt, Germany) and were used directly without further purification. All solvents with analytical grades were purchased from Merck (Darmstadt, Germany). Monosodium phosphate (NaH2 PO4) was obtained from Fluka (Buchs, Switzerland). The SeaKem LE Agarose Lonza was used in this study. Milli- Q system (Millipore, Milford, MA, USA) was utilized to obtain HPLC grade water. The Eppendorf safe-lock 0.5 mL PP tubes were obtained from Eppendorf AG (Hamburg, Germany).

2.3. Chromatographic separation conditions The used HPLC assembly was a Rigol system (Beijing, China) equipped with a solvent degasser (L-3000), a quaternary pump (L-3245), a system controller (L-3400), a manual injection valve equipped with a 20 ␮L injection loop, and a variable wavelength UV analyzer (L-3500). Samples were subjected to the separation by an Optimal ODS-H analytical column (250 mm × 4.6 mm, 5 ␮m) (Capital HPLC, UK). The data were acquired using YL Clarity software. The chromatographic separation mobile phase was the 10 mM NaH2 PO4 buffer (pH 3.0) (A) and acetonitrile (B). The gradient chromatography protocol was as follows: 0−10 min, 30–70 % B, 10–12, 70 % B, 12−15 min, 70–30 % B. The analytical wavelength detected at UV spectra was set to as 210 nm utilized for all measured drug compounds. 2.4. Preparation of gel membrane The agarose powder was dispersed to deionized water and heated in a microwave oven at 90 ◦ C for 30 s. Afterwards, the hot solution was quickly and quantitatively transported into an Eppendorf tube by a disposable micropipette and kept at 4 ◦ C for 1 h to become a gel [15]. After cutting down the Eppendorf tube which served as an extraction chamber, the tube was placed in the holder in the way that half of the gel was in contact with the DP and half of it was stuck inside the holder. 2.5. Extraction procedure Fig. 1 depicts the setup utilized to implement the suggested extraction procedure. The DC power supply used was a model PV300 (Mobtaker Aryaei J., Zanjan, Iran) with programmable voltage in the range of 0–600 V, providing currents in the range of 0 −0.5 A. Platinum electrodes (0.2 mm in diameter) were purchased from Pars Pelatine (Tehran, Iran Also for improving of repeatability of IG-EME, a homemade set-up was used to fix the electrodes to the holder (Fig. 1). The stirring was carried out in a Heidolph MR 3001 K magnetic stirrer (Schwabach, Germany) equipped with 1.5 mm × 8 mm magnetic bars. An appropriate portion of sample solution (7.0 mL at pH 6.0, HCl) containing model drug compounds was transferred into a 10 mL glass vial. The Eppendorf tube constituted the agarose gel functioning as membrane and AP (pH 3.0, HCl), was immersed in to the DP. Here, the main modification compared to previous assembly involved the insertion of negative electrode inside the gel membrane (Fig. 1. After placing the positive electrode into the sample solution, stirred at 500 rpm, the 25 V voltage was turned on and the transport of analytes was carried out for 30 min. Afterwards, the gel membrane was removed and centrifuged at 12,000 rpm for 5 min to release the “trapped aqueous AP” apart from the gel material. Then, the AP containing enriched target analytes was then withdrawn with a HPLC micro-syringe and subjected to the HPLC for analysis.

2.2. Standards and biological sample solutions The stock solutions of each drug (1000 mg L−1 ) was diluted with methanol and stored at 4 ◦ C (to the note after one month no evidence of decomposition was observed). The daily prepared standard solutions were diluted with HPLC grade water. Drugfree human plasma was obtained from Taleghani Hospital (Tehran, Iran) and drug-free human urine-1 and drug-containing human urine-2 samples were obtained from a healthy volunteer and patient (40-year-old male) undergoing COD treatment, respectively. Plasma and urine samples were initially diluted at 1:5 and 1:10 ratio, respectively, with HPLC grade water. To adjust the pH of the solution to 6.0, the 0.1 M NaOH or 0.1 M HCl was used.

3. Results and discussion 3.1. Optimization of IG -EME procedure The essential parameters, namely agarose gel composition, agarose concentration, thickness of membrane serving simultaneously as an AP volume, applied voltage, pH of the gel and DP, extraction time, and stirring speed were optimized to enhance the extraction efficiency. 3.1.1. Influence of the agarose gel composition In this work, whereas agarose gel acted as the both filter (membrane) and AP, the study of gel composition was the most pivotal.

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Fig. 1. Schematic illustration of the proposed EME setup.

The effect of gel composition on the extraction efficiency was studied by the preparation of membrane using different solvents such as water, ethanol, methanol, and acetonitrile. To prepare gel membranes containing organic solvents inside the gel, the gel membrane (concentration of agarose, 1% (w/v)), was dipped in each organic solvent (ethanol, methanol or acetonitrile) for a specified time. Under this condition, the water in the structure of gel membrane was replaced with related organic solvent [20]. To ensure impregnation of membrane with organic solvent, the gel material was centrifuged at 12,000 rpm for 5 min to squeeze the organic solvent from membrane. Ultimately, the collected solvent was analyzed by the gas chromatography (GC). The results showed that 70.3, 73.5 and 55.8 % (v/v) of ethanol, methanol and acetonitrile was impregnated in the gel, respectively (data not shown). To investigate the effect of agarose gel composition on the extraction efficiency, the extraction procedure was examined using different membrane types containing water or organic solvents. As shown in Fig. 2, the organic solvent impregnated membranes showed similar results compared to the aqueous ones. Moreover, gel fabrication in water and controlling its pH is much simpler and water serves a green chemistry as well. Thus, a water-gel-based membrane was chosen for further studies.

3.1.2. Influence of the agarose concentration The concentration of agarose determined the pore size and fragility of the network that protects the AP [21]. The different agarose concentrations were prepared in the range of 0.8–3% (w/v) in water. The extraction efficiency was found to be optimal when

Fig. 2. Effect of agarose gel composition. Extraction conditions: voltage: 15 V; pH of the DP: 5.0; pH of the gel: 3.0; extraction time: 30 min; stirring rate: 500 rpm; thickness of the agarose gel: 15 mm; concentration of agarose: 1% (w/v). Error bars were obtained based on 3 replicates.

agarose concentration was 1% (w/v) (Fig. 3A). According to previous study, when the concentration of agarose increases the pore size of membrane decreases [22]. As a result, the analyte entering into the smaller pore size of the membrane becomes more difficult. On the other hand, at agarose concentrations lower than 1% (w/v),

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Fig. 3. Effect of A) concentration of agarose, and B) volume of the gel on the extraction efficiency. Extraction conditions: voltage: 15 V; pH of the DP: 5.0; pH of the gel: 3.0; extraction time: 30 min; stirring rate: 500 rpm; thickness of the agarose gel: 20 mm (for A); concentration of agarose: 1 % (w/v) (for B). Error bars were obtained based on 3 replicates.

the gel was too fragile and collapsed during the extraction. Therefore, the optimal agarose concentration for membrane fabrication was determined to be 1% (w/v).

3.1.3. Influence of membrane thickness (volume of the acceptor phase) The thickness of gel membrane determined the required volume of the AP. In this work, the range of 350−550 ␮L which is related to the 5−25 mm thickness of gel membrane was chosen to study the effect of volume of the AP on the extraction efficiency. Whereas the gel membranes were prepared in Eppendorf microtube with conic bottom shape thus there is no linear relationship between the volume and thickness. The results (Fig. 3B) depicts that the AP with 450 ␮L which related to thickness of 15 mm showed the maximum extraction efficiency. The selected thickness which related to the AP volume was sufficient to enhance the enrichment of the analytes and support the trace analysis. Also by changing the gel volume from 450 to 550 ␮L, the thickness of gel was increased from 15 mm to 25 mm and results showed that extraction efficiency decreased to a great extent. It can be attributed to the fact that analytes need more electrical potential or more extraction time to migrate from the DP to the AP. To find compromise toward a high balance among the gel thicknesses values, the contact area of gel and the final concentration of extracted analytes, the thickness of 15 mm was selected for further studies.

Fig. 4. Effect of A) pH of the gel, and B) pH of the DP on the extraction efficiency. Extraction conditions: Concentration of agarose: 1 % (w/v); thickness of the agarose gel: 15 mm; voltage: 15 V; extraction time: 30 min; stirring rate: 500 rpm; pH of the DP: 5.0 (for A); pH of the gel: 3.0 (for B). Error bars were obtained based on 3 replicates.

3.1.4. Influence of pH of gel and sample solution In EME, according to theoretical model, to achieve the maximum degree of extraction efficiency, the analytes should be converted to their ionic forms. By the following equation, pH values of the DP and the AP determined the ion balance (␹) in this extraction system.

  ∗ C + C i ih k kh =   Ci0 +

C∗ k k0

(1)

i

Where Cih is concentration of the cationic substance in the DP, C∗ kh is concentration of the anionic substance in the DP, Ci0 is concentration of the cationic substance in acceptor phase, and C∗ k0 is concentration of the anionic substance in the AP. According to the equation (3) [23], maximum response was obtained at minimum ␹. As already mentioned, the water captured inside the gel acts as the AP. When target analytes enter the gel pores, the pH of gel plays an important role to get the high extraction efficiency. To study the pH effect of gel, the gel membrane with concentration of 1% (w/v) agarose was prepared by dissolving appropriate amounts of agarose in the aqueous solutions with different pHs (i.e., 1.5–5.0). Results showed that the gels with pH < 3.0 were very loose and thus cannot be used in this extraction system. As illustrated in Fig. 4A, maximum extraction yield was obtained at pH 3.0 while at higher pH values of gel, the extraction efficiency was significantly reduced. The electrokinetic migration can be achieved when basic drugs became ionized, thus pH value of sample solution is also important. According to pKa values of the model drugs

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Table 1 Analytical performance of the proposed IG-EME method for determination of MOR and COD in the in the pure DI water. RSDc % Drug

r2

LOQa

LODa

Linearitya

Recoveryb %

Morphine Codeine

0.998 0.998

5.0 5.0

1.5 1.5

5.0–1000 5.0–1000

73.8 67.7

a b c

Intraday

Interday

100

500

100

500

6.0 8.5

5.6 7.9

10.3 9.9

6.7 8.7

Concentration is based on ng mL−1 . Recovery was obtained for 100 ng mL−1 of each drug (n = 3). (n = 3).

(MOR: 8.21 and COD: 8.20), pH of the DP was tested in the range of 3.0–7.0. As shown in Fig. 4B, extraction efficiency increased proportionally to the pH increase from 3.0–6.0, due to decreasing value of ␹. Thus, the pH of 6.0 was utilized as the optimal pH for the DP in the next experiment.

3.1.5. Influence of applied voltage The influence of applied voltage was tested at various voltages, in the range of 0–40 V. As shown in Fig. 5A, when no voltage was applied, the target analytes could transfer from the DP to the pores of gel due to diffusion mechanism. The results showed that by increasing the voltage from 0 to 25 V, the extraction efficiency increased. According to the Nernst–Planck equation [23], by increasing potential difference between electrodes, an improve´ ment in analytesflux is observed. But a further increase in voltage from 25 to 40 V led to the decreased extraction performance which is related to the bubbles formed at the electrodes by electrolysis [24]. Furthermore, the value of electrical current passing through the membrane was continuously measured by applying different voltages. The results showed that the electrical current increased with higher applied voltage. Relying on this fact that the larger current magnitudes resulted in lower extraction recoveries [25], the optimal electrical potential was found to be 25 V, establishing an electrical current of about 0.6 mA.

3.1.6. Influence of the extraction time Extraction time is also pivotal to determine the total amount of analytes transported from the DP (sample) to the AP [26]. Thus, extraction time was tested, in the range of 15−50 min. Fig. 5B indicated that extraction efficiency improved with an increase in the extraction time from 15 to 30 min. After this interval, the extraction efficiency decreased as the gel membrane become unstable and tended to be destroyed. In that regard, 30 min was selected as the optimum extraction time for further studies.

3.1.7. Influence of the stirring rate To elevate mass transfer and reduce the time needed to achieve thermodynamic equilibrium, stirring rate of the sample played an important role [27]. According to Fig. 5C, the effect of stirring rate was investigated within the range 0–1250 rpm. Because of the convection effects, the extraction efficiency enhanced with increased stirring rate, from 0 to 500 rpm. At higher mixing rates, the bubble formation in sample solution decreased the extraction efficiency [28]. Therefore, 500 rpm was selected as the optimal stirring rate. In order to check the EEO flow in this set-up, the AP volume before and after IG-EME should be measured. The results showed that the AP volume increased only about 10 ␮L after IG-EME process. While in conventional G-EME, the volume of AP increased about 50–100 ␮L [15–18]. Thus, with this new modification EEO was diminished significantly.

Fig. 5. Effect of A) voltage, B) extraction time, C) stirring rate on the extraction efficiency. Extraction conditions: Concentration of agarose: 1 % (w/v); thickness of the agarose gel: 15 mm; pH of the DP: 6.0; pH of the gel: 3.0; stirring rate: 500 rpm for (A, B); extraction time: 30 min (for A, C); voltage: 25 V for (B, C). Error bars were obtained based on 3 replicates.

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Fig. 6. Typical chromatograms obtained after IG-EME from non-spiked and spiked (80 ng mL−1 of each drug) in A) plasma, B) urine-1 and C) urine-2 samples.

3.2. Analytical performance of proposed method

3.3. Analysis of real samples

To evaluate the performance of the suggested IG-EME procedure for the determination of model drugs, the limit of detection (LOD), limit of quantification (LOQ), linearity, precision, and recovery (R), were examined under the optimal extraction conditions (Table 1). The experiment of linearity was studied in the range of different levels of analytes (i.e., 5.0−1000 ng mL−1 ). Values for the coefficient of determination (r2 ) were higher than 0.997 for the model compounds. The LOD and LOQ were estimated according to an S/N of 3 and 10, respectively. The acceptable LOD and LOQ values were 1.5 ng mL−1 and 5.0 ng mL−1 , respectively. Recoveries were found in the range of 67.7–73.8% (Table 1). Relative standard deviation (RSD%) of the suggested method, expressed as intra-day precision (repeatability), was evaluated by extracting three independent samples spiked at 100.0 and 500.0 ng mL−1 which was found to be in the range of 5.6–8.5 %, respectively (Table 1). In addition, the inter-day precision was investigated by analyzing three samples spiked at 100.0 and 500.0 ng mL−1 in three consecutive days and the RSD% values were found to be within the range of 6.7–10.3 %.

The application of the suggested assembly was finally studied using real biological samples such as plasma and urine. The experimental results revealed that no drugs were found in biological samples, but only in “Urine 2” sample, 56.0 ng mL−1 of COD was determined as real amount (Fig. 6C). To investigate matrix effect, the samples were diluted according to Section 2.2 and spiked with each of the model drugs at 80.0 and 800.0 ng mL−1 . The results of three replicates of the suggested extraction method upon real samples, are shown in Table 2. Their relative recoveries (RR%) were determined to be in the ranges of 78–102 % (Table 2). Non-spiked and spiked chromatograms of plasma and urine samples are depicted in Fig. 6. 3.4. Comparison of proposed method with conventional EME and G-EME The validity of suggested method was compared with previous classical EME performances (Table 3) [15,29–31]. The sensitivity is comparable or even better than the sensitivity of the previous EME methods, by which the extraction of the model basic drugs was measured. In EME, the MOR with high polarity could be extracted

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Table 2 Determination of model drugs in the urine and plasma samples. Sample

Spiked Concentration (ng mL−1 )

Analyte

Morphine Plasma Codeine

Morphine Urine-1 Codeine Morphine Urine-2b Codeine a b

Added

Founded (mean ± SD)

0.0 80.0 800 0.0 80.0 800 0.0 80.0 800 0.0 80.0 800 0.0 80.0 0.0 80.0

n.da 68.0 ± 6.2 792 ± 67 n.da 62.4 ± 6.1 760 ± 69 n.da 72 ± 7.3 816 ± 68 n.da 64.0 ± 6.2 744 ± 54 n.da 72.8 ± 7.0 56.0 ± 4.9 119.2 ± 11.2

RR%

RSD%

– 85 99 – 78 95 – 90 102 – 83 93 – 91 – 79

– 9.1 8.5 – 9.8 9.1 – 10.1 8.3 – 9.7 7.2 – 9.6 8.8 9.4

n.d. non detected. Urine-2 sample was collected from a patient undergoing COD treatment.

Table 3 Comparison of analytical performance of IG-EME method with other classical EME methods. Analytical method

Analyte

Membrane Composition

LOD (ng mL−1 )

Recovery %

RSD %

Ref.

EME-DPV

MOR MOR COD MOR MOR MOR COD

HF containing (NPOE + TEHP + DEHP)

1.5 19.0 59.0 25.0 1.5 1.5 1.5

71–76 – – 2.1 67.4 73.8 67.7

– – – 2.8 11.4 5.6 7.9

[29]

EME-DPV EME-HPLC GEL-EME IG-EME

HF containing (1-octanol + DEHP) HF containing (NPOE + DEHP) Agarose Gel Agarose Gel

only in presence of carrier reagent (DEHP or TEHP) into the SLM [28,29]. Conversely, in G-EME, the model basic drugs with high polarities can be extracted without using any reagent in the membrane. Moreover, with gel membrane for the proposed IG-EME setup, it is possible to increase the volume of AP to enhance extraction efficiency, without changing the size of the flat gel membrane. This has not been an option in conventional EME where hollow fibers serve as membrane and the volume of the AP is limited to the internal volume of the lumen of the hollow fiber. Also, one of the best features of agarose gel over hollow fiber is easy fabrication of the respective membrane at different thicknesses and shapes. This is while hollow fibers’ dimensions and shapes are limited by commercial suppliers. The other advantage of an agarose gel membrane is its low price and highly safe nature. Because only water is necessary to fabricate membrane at final form. Eventually, IGEME was proposed to achieve a main objective for addressing EEO phenomenon which was a critical problem in conventional G-EME.

4. Conclusions In this work, G-EME was modified toward IG-EME serving as a two-phase G-EME mode for the extraction of MOR and COD (as model basic drugs) in biological samples. In this setup, the AP did not function as an individual/free phase (i.e., AP was trapped into the gel membrane material, thus SLAP was created). This modification contributed to diminish the EEO phenomenon which was a critical problem in conventional G-EME. The decrease in EEO effect along with the entrapment of transported anlaytes inside the gel membrane resulted in higher extraction efficiencies and enrichment factors. Moreover, the model polar drugs were extracted without using any ion-pair/carrier reagents while this was impossible in classical EMEs. To sum up, the suggested extraction setup serves advantages such as simplicity, feasibility and most

[30] [31] [15] This work

importantly environmentally friendly medium compared to the conventional EME. Declaration of Competing Interest There are no financial or commercial conflicts of interest. Acknowledgement This research was supported financially by the Shahid Beheshti University and Research Institute of Applied Sciences (ACECR). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jpba.2020. 113175. References [1] J. Płotka-Wasylka, K. Owczarek, J. Namiesnik, Modern solutions in the field of microextraction using liquid as a medium of extraction, TrAC-Trends Anal. Chem. 85 (2016) 46–64. [2] T. Barri, J.A. Jonsson, Advances and developments in membrane extraction for gas chromatography techniques and applications, J. Chromatogr. A 1186 (2008) 16–38. [3] H. Tabani, S. Nojavan, M. Alexoviˇc, J. Sabo, Recent developments in green membrane- based extraction techniques for pharmaceutical and biomedical analysis, J. Pharm. Biomed. Anal. 160 (2018) 244–267. [4] E. Carasek, J. Merib, Membrane-based microextraction techniques in analytical chemistry: a review, Anal. Chim. Acta 880 (2015) 8–25. [5] N. Jakubowska, Z. Polkowska, J. Namiesnik, Analytical applications of membrane extraction for biomedical and environmental liquid sample preparation, Crit. Rev. Anal. Chem. 35 (2005) 217–235. [6] S. Pedersen-Bjergaard, K.E. Rasmussen, Electrokinetic migration across artificial liquid membranes. New concept for rapid sample preparation of biological fluids, J. Chromatogr. A 1109 (2006) 183–190.

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