Novel deep eutectic solvent-based ultrasounds-assisted dispersive liquid-liquid microextraction with solidification of the aqueous phase for HPLC-UV determination of aromatic amines in environmental samples.

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Novel deep eutectic solvent-based ultrasounds-assisted dispersive liquidliquid microextraction with solidification of the aqueous phase for HPLC-UV determination of aromatic amines in environmental samples. Justyna Werner Poznan University of Technology, Department of Chemical Technology, Berdychowo 4, 60-965 Poznan, Poland

ARTICLE INFO

ABSTRACT

Keywords: Dispersive liquid–liquid microextraction Aromatic amines Deep eutectic solvent Ultrasounds Solidification of aqueous phase

In this study, a green and efficient sample preparation method using a deep eutectic solvent-based ultrasoundsassisted dispersive liquid–liquid microextraction with solidification of the aqueous phase (DES-UA-DLLME-SAP) followed by HPLC-UV was developed for preconcentration and determination of aromatic amines in aqueous environmental samples. In the proposed method, a novel deep eutectic solvent (DES) characterized by low density was prepared by mixing trihexyl(tetradecyl)phosphonium chloride and decanol at a molar ratio of 1:2. Ultrasounds were used to disperse the extractant in the aqueous phase of the sample. Then, the phases were separated by centrifugation, after which the aqueous phase was frozen and the surface DES phase was dissolved in a small volume of methanol before injection into the chromatograph. Various factors, including the selection of extractant and its volume, pH of the sample, duration of ultrasounds treatment, the time and rate of centrifugation and salt addition, were investigated and optimized. Under optimal conditions (40 µL of DES, pH = 12, 60 s of ultrasound use, 10 min/4500 rpm of centrifugation, 40 mg of NaCl), the proposed method allowed to achieve good precision (n = 6) between 2.9 and 6.2% at 0.4, 5.0 and 40.0 ng mL−1 levels, respectively. The preconcentration factors were equal to 119, 116 and 121 for 2-chloroaniline, 4-chloroaniline and 1naphthylamine, respectively. The limits of detection were equal to 0.07 ng mL−1 for 2-chloroaniline, 0.11 ng mL−1 for 4-chloroaniline and 0.08 ng mL−1 for 1-naphthylamine. The proposed method was successfully applied for determination of aromatic amines in aqueous environmental samples with a good recoveries in the range of 85.1–99.9%

1. Introduction Aromatic amines are widely used organic compounds and their major sources in the environment include important industrial sectors, such as oil refining, production of synthetic polymers, dyes, adhesives, perfumes, pharmaceuticals, pesticides and explosives. They can also be produced during the combustion of diesel or rubber as well as in tobacco smoke [1–3]. The increasing production and use of these compounds explains their occurrence in the environment, which is associated with a potential risk of human exposure. Aromatic amines are potential carcinogenic and toxic agents, which constitute an important class of environmental pollutants and must be monitored at concentration levels lower than 30 µg mL−1 [2,3]. Gas chromatography, high performance liquid chromatography, capillary electrophoresis and UV–Vis spectrophotometry have been used for the determination of aromatic amines [4,5]. However, in cases when it is not possible to use a very sensitive analytical technique, the

preconcentration step is necessary. Most often, pretreatment techniques such a magnetic solid phase extraction (MSPE) [6–8], solid phase microextraction (SPME) [9–11], hollow fiber liquid phase microextraction (HF-LPME) [12–13] and dispersive liquid-liquid microextraction (DLLME) [14–16] were used in order to enrich trace amounts of aromatic amines. Dispersive liquid-liquid microextraction (DLLME) is a well-known variant of the LPME technique. In the DLLME technique, a mixture of a water-immiscible extractant and a water-miscible dispersing solvent is injected into an aqueous sample in order to obtain a cloudy solution. The analytes in the sample are extracted into fine droplets of the extractant, then the mixture is centrifuged [17,18]. The DLLME technique is rapid, requires low volumes of the extractant as well as dispersing solvent and is characterized by high recovery and preconcentration factor (PF). The degree of dispersion is one of the most important factors for effective extraction of analytes using DLLME technique. Application of ultrasounds (as a dispersing agent) in the DLLME technique

E-mail address: [email protected]. https://doi.org/10.1016/j.microc.2019.104405 Received 1 September 2019; Received in revised form 4 November 2019; Accepted 6 November 2019 0026-265X/ © 2019 Elsevier B.V. All rights reserved.

Please cite this article as: Justyna Werner, Microchemical Journal, https://doi.org/10.1016/j.microc.2019.104405

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(UA-DLLME) accelerates the formation of fine droplets of the extractant and the mass transfer of the analytes from the sample phase to the extractant phase. Additionally, it eliminates the necessity to use a dispersing solvent, which corresponds well with the principles of Green Chemistry [19]. In the DLLME technique, selection of a water-immiscible, efficient extractant is also very important. In recent years, volatile organic compounds (VOCs) and then ionic liquids (ILs) [20,21] have been used as extractants. However, due to their properties such as low volatility, low toxicity, biodegradability, low-costs and ease of preparation - deep eutectic solvents (DESs) [22–26] have become an interesting alternative to ILs and VOCs. DESs are compounds which are formed due to hydrogen bond interaction, by mixing an appropriate amount of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) [22,23]. Another innovation in the DLLME technique was the introduction of the solidification of a floating organic drop (DLLME-SFO) [27], including the solidification of a deep eutectic solvent (SDES) [28–32] which is possible in case of extractants lighter than water, with a melting point lower than room temperature. However, the introduction of solidification of the aqueous phase (DLLME-SAP) may be an interesting solution, especially for extractants lighter than water, with a melting point much lower than the melting point of water [33–34]. The aim of the present study was to develop a green, simple and efficient method of deep eutectic solvent-based ultrasound-assisted dispersive liquid-liquid microextraction with solidification of the aqueous phase for preconcentration of aromatic amines in the environmental samples followed by HPLC-UV determination. The main novelty of the proposed method includes the use of newly synthesized, non-toxic and water-immiscible DES which consist of trihexyl(tetradecyl)phosphonium chloride:decanol at a molar ratio of 1:2 as a low density extractant as well as the use of ultrasounds as an effective dispersing agent. The proposed, environmentally friendly DESUA-DLLME-SAP/HPLC-UV method has not been reported to date.

process the chromatographic data. A Sonopuls HD 70 ultrasonic homogenizer (70 W, 20 kHz, Bandelin, Germany) equipped with a 2 mm titanium probe was used as a dispersing agent. A pH-meter (EL20, Mettler Toledo, Switzerland) with lab pH electrode (type LE407) was used for pH measurements. A centrifuge (Hettich EBA 20, Tuttlingen, Germany), with a centrifugation rate in the range from 500 to 6000 rpm, was used for separation of phases. 2.3. Samples In this study, four aqueous environmental samples were collected to validate the proposed method. The samples included lake water (Malta Lake, Poland), river water (Cybina River, Poland), sea water (Baltic Sea, Poland) and melted snow water (Paproć, Poland). All samples were filtered using syringe filters (with 0.25 µm micro-pore polytetrafluoroethylene membranes) before analysis and stored in glass bottles at the temperature of 4 °C. 2.4. Synthesis of deep eutectic solvents The synthesis of different deep eutectic solvents was carried out separately by mixing trihexyl(tetradecyl)phosphonium chloride as a hydrogen bond acceptor with decanol or dodecanol as the hydrogen bond donors at molar ratios of 1:1, 1:2, 1:3 (HBA:HBD) in a 10 ml glass vessel with a small magnetic rod. The glass vessel was kept sealed with a screw cap to maintain the temperature at 60 ⁰C with stirring for 40 min to form a homogeneous phase of DES. The abbreviations and composition of the synthetized DESs were presented in Table 1. 2.5. DES-UA-DLLME-SAP procedure A 15 mL aliquot of deionized water spiked with 10 ng mL−1 of 2chloroaniline, 10 ng mL−1 of 4-chloroaniline and 20 ng mL−1 of 1naphthylamine or aqueous sample solution was transferred into a glass test tube. The pH of the solution was adjusted to 12 using 1 M NaOH. Then, 40 μL of DES-2 ([P14,6,6,6]Cl: decanol, 1:2) and 40 mg of NaCl (ionic strength) were added. The 2 mm titanium probe of the ultrasonic homogenizer (with a power of 45 W) was immersed into the mixture for 60 s and a cloudy solution was formed. Afterwards, the aromatic amines were extracted into the DES phase. After centrifugation for 10 min at 4500 rpm, the tube containing two separated phases was placed in a freezer at −18 °C to carry out the solidification of the aqueous phase. Then, the DES phase was taken up with a microsyringe, dissolved in 80 μL of methanol and injected into the HPLC system.

2. Material and methods 2.1. Reagents and solutions 2-Chloroaniline (purity ≥99.5%), 4-chloroaniline (purity ≥98.0%), 1-naphthylamine (purity ≥99.0%) and trihexyl(tetradecyl)phosphonium chloride ([P14,6,6,6]Cl, purity ≥95.0%) were purchased from Sigma–Aldrich (Poland). 1-Decanol (purity ≥98.0%) and 1-dodecanol (purity ≥98.0%) were purchased from Merck (Germany). The pH of the samples was adjusted using sodium hydroxide (30%, Suprapur®, Merck, Germany) after appropriate dilution. Sodium chloride (purity 99.99% Suprapur®, Merck, Germany) was used. Methanol (gradient grade for LC, LiChroSolv®, Merck, Germany) was used as a solvent for the extractant prior to chromatographic analysis as well as an eluent for the mobile phase. High-purity deionized water and double distilled water (quartz apparatus, Bi18, Heraeus, Germany) were used during this study. Fresh stock solutions (100 µg mL−1 in methanol) of 2-chloroaniline, 4chloroaniline and 2-naphthylamine were prepared every week and stored at 4 °C before use. Working standard solutions of aromatic amines were prepared every day by diluting the stock solutions with high-purity water.

3. Results and discussion 3.1. Characterization of the deep eutectic solvent The DES-2, which was successfully used for microextraction in this work, was prepared using trihexyl(tetradecyl)phosphonium chloride and decanol. The structural characteristic of the newly synthetized DES was evaluated using Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of trihexyl(tetradecyl)phosphonium chloride (green line) and DES-2 (blue line) are shown in Fig. 1. A broad band at Table 1 Composition of the DESs synthetized.

2.2. Instrumentation Aromatic amines were determined using a Hewlett Packard 1100 HPLC system equipped with an isocratic pump and an UV detector. Separation of the analytes was carried out using a Inertsil® ODS-3 column (150 × 4.6 mm i.d., 4 μm) in reserved-phase mode. The mobile phase consisted of methanol/water (70/30, v/v), the flow rate of the mobile phase was equal to 1.2 mL min−1 and the detection wavelength was set at 240 nm. The ChemStation software was used to acquire and 2

Abbreviation

HBA

HBD

Molar ratio of HBA:HBD

DES-1 DES-2 DES-3 DES-4 DES-5 DES-6

[P14,6,6,6]Cl [P14,6,6,6]Cl [P14,6,6,6]Cl [P14,6,6,6]Cl [P14,6,6,6]Cl [P14,6,6,6]Cl

decanol decanol decanol dodecanol dodecanol dodecanol

1: 1: 1: 1: 1: 1:

1 2 3 1 2 3

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Fig. 1. The FT-IR spectra of trihexyl(tetradecyl)phosphonium chloride (green line) and DES-2 (blue line).

3500–3000 cm−1, with a maximum at 3320 cm−1 is characteristic for the stretching vibrations of the OeH group derived from the intermolecular hydrogen bonding between trihexyl(tetradecyl)-phosphonium chloride and decanol in the newly synthetized DES-2. In the FT-IR spectrum of DES-2, the bands located at 2925 and 2854 cm−1 correspond to the stretching vibrations of the CeH groups, while bands at 1466 cm−1 are associated with the scissoring vibrations of the CeH groups and bands at 1059 cm−1 correspond to the stretching vibrations of the CeO groups.

3.2.2. The volume of the extractant The volume of DES is an important parameter of the proposed method because it can directly influence the preconcentration factor and extraction efficiency. Different volumes of the DES-2, i.e. 10, 20, 30, 40, 50, 60, 70 µL, were investigated. For volumes below 40 µL of the extractant, the cloudy solution could not be observed and thus a lower analytical signal was obtained. Volumes of the extractant higher than 40 µL did not cause of a significant change in the analytical signals. Therefore, 40 µL of DES-2 was selected to extract the aromatic amines in order to obtain a high preconcentration factor (Fig. 3A).

3.2. Optimization of the DES-UA-DLLME-SAP conditions

3.2.3. The pH of the samples Aromatic amines are weak basic compounds and the pKb of 2chloroaniline, 4-chloroaniline and 1-naphthylamine are equal to 11.4, 10.0 and 10.1, respectively. Aromatic amines under acidic pH exist as positive ions, which increases their water-solubility and decreases their extraction to the DES phase. Therefore, the effect of sample pH was investigated in the range of 8–14 and sodium hydroxide was added to adjust the alkalinity. The analytical signals were highest at pH=12 and these conditions were used for further experiments. The results were presented in Fig. 3B.

3.2.1. Selection of the extractant The selection of an appropriate DES as an extractant is one of the most important factors in the proposed method. Some properties of DES, such as density lower than water, insolubility or low solubility in water, a melting point much lower than the melting point of water, low toxicity and high extraction efficiency of analytes, have been considered. Six deep eutectic solvents (Table 1) were synthetized and used in this study. The results indicate that the use of DES-2 ([P14,6,6,6]Cl: decanol, 1:2) allowed to achieve the highest analytical signals for extraction of aromatic amines, therefore it was selected for further studies (Fig. 2).

3.2.4. Effect of the NaCl addition The addition of a small amount of inorganic salt results in an

Fig. 2. Effect of selection of extractant on analytical signals of aromatic amines obtained using the DES-UA-DLLME-SAP/HPLC-UV method. Conditions: sample 15 mL (containing 5 ng mL−1 of each analyte); pH = =12; DES - 70 µL; NaCl - 80 mg; ultrasounds - 120 s; centrifugation - 20 min/6000 rpm (time/rate). 3

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Fig. 3. Effect of the variable factors on the performance of DES-UA-DLLME-SAP method: (A) the volume of the extractant, (B) the pH of the sample, (C) NaCl addition (the ionic strength effect), (D) duration of ultrasounds use. Conditions: sample - 15 mL (containing 5 ng mL−1 of each analyte); pH = =12; DES - 40 µL; NaCl - 40 mg; ultrasounds - 60 s; centrifugation - 10 min/4500 rpm (time/rate).

to facilitate the separation of phases.

Table 2 The analytical performance characteristics of the proposed method for the determination of aromatic amines. Analytical figures

2-chloroaniline

4-chloroaniline

1-naphthylamine

Linearity range [ng mL−1] Correlation coefficient (R2) LOD [ng mL−1] LOQ [ng mL−1] Precision RSD 0.4 [ng [%] mL−1] (n = 6) 5 [ng mL−1] 40 [ng mL−1] Preconcentration factor

1.0–200.0 0.9984 0.07 0.23 4.8

1.0–200.0 0.9988 0.11 0.36 6.2

0.5–250.0 0.9975 0.08 0.26 6.0

2.9

5.8

4.5

3.2

4.9

3.9

119

116

121

3.2.5. The duration of the ultrasounds treatment The use of ultrasounds in the DES-UA-DLLME-SAP technique was important for eliminating the use of a volatile and toxic organic solvent as a dispersing agent. Ultrasound energy can increase the surface contact and accelerate the mass transfer between the aqueous phase and DES phase, resulting in a shorter extraction time and higher extraction efficiency. In this study, an ultrasonic probe was immersed into the mixture of aqueous sample solution and extractant. The solution became cloudy due to the dispersion of DES droplets into the aqueous phase. The effect of sonication time on the extraction efficiency was studied in the range of 30–120 s. The duration of ultrasounds treatment equal to 60 s was selected. The results were presented in Fig. 3D. 3.2.6. The rate and time of the centrifuging Centrifugation was used to efficiently separate the DES phase from the aqueous phase after the extraction. The effect of centrifugation rate on the effective separation of phases was studied in the range of 1500–6000 rpm for 20 min. Below 3500 rpm it was not possible to achieve a complete separation of phases. Beyond 4500 rpm, the analytical signals remained constant and this value was selected. In the next step, the centrifugation was conducted between 5–20 min at 4500 rpm. It was observed that after 10 min the phases were completely separated and this value was selected.

increase of extraction efficiency of the analytes from the sample and the efficiency of the separation of aqueous sample and extractant phases after centrifugation. The effect of the NaCl on the separation of phases was evaluated by adding various amounts of NaCl (10–80 mg in 15 mL) into the solution or no salt was added to the solution, as presented in Fig. 3C. When no sodium chloride was added, low analytical signals of aromatic amines were observed, because the DES phase could not be completely separated from the sample solution and lower amounts of the extractant were collected. It seems that when low amounts (less than 40 mg) of NaCl were used, the emulsion did not break well, and the phase separation did not occur completely. Meanwhile, more than 40 mg NaCl reduced the extraction efficiency, probably due to the decrease of the distribution coefficient of the analytes desired in the DES, due to increased ionic strength of the solution. A value of 40 mg was selected as the optimal amount of NaCl in the sample solution in order

3.3. Analytical performance of the proposed method The analytical performance of the proposed DES-UA-DLLME-SAP method was investigated under the optimized conditions. A series of experiments was carried out in order to determine the linearity ranges, 4

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Table 3 The analytical results for determination and recoveries of aromatic amines in the aqueous environmental samples by the DES-UA-DLLME-SAP/HPLC-UV method with using the optimized conditions. Sample

Analytes

Blank [ng mL1 ]

Spiked 0.40 [ng mL-1] Measured* RSD [%] [ng mL-1]

Recovery [%]

Spiked 5.00 [ng mL-1] Measured* RSD [%] [ng mL-1]

Recovery [%]

Spiked 40.00 [ng mL-1] Measured* [ng RSD [%] mL-1]

Recovery [%]

Lake water1

2-chloroaniline 4-chloroaniline 1-naphthylamine 2-chloroaniline 4-chloroaniline 1-naphthylamine 2-chloroaniline 4-chloroaniline 1-naphthylamine 2-chloroaniline 4-chloroaniline 1-naphthylamine

nd nd nd nd nd nd nd nd nd nd nd nd

0.37 ± 0.03 0.36 ± 0.02 0.39 ± 0.03 0.40 ± 0.02 0.39 ± 0.02 0.38 ± 0.03 0.36 ± 0.03 0.34 ± 0.02 0.38 ± 0.02 0.35 ± 0.02 0.38 ± 0.01 0.38 ± 0.03

92.5 90.0 97.5 99.9 97.5 95.0 90.0 85.1 95.0 87.5 95.0 95.0

4.77 ± 0.32 4.84 ± 0.40 4.72 ± 0.35 4.69 ± 0.22 4.81 ± 0.39 4.90 ± 0.43 4.54 ± 0.40 4.61 ± 0.37 4.49 ± 0.33 4.63 ± 0.27 4.76 ± 0.31 4.87 ± 0.41

95.4 96.8 94.4 93.8 96.2 98.0 90.8 92.2 89.8 92.6 95.2 97.4

39.19 ± 1.38 37.79 ± 2.61 38.82 ± 1.83 37.87 ± 2.23 37.69 ± 2.37 37.31 ± 2.85 36.97 ± 3.42 36.74 ± 2.81 37.02 ± 2.67 37.30 ± 3.02 35.66 ± 3.28 37.01 ± 3.11

97.9 94.5 97.1 94.7 94.2 93.3 92.4 91.9 92.6 93.3 89.2 92.5

River water2 Sea water3 Melted snow water4 1

8.1 5.5 7.7 5.0 5.1 7.9 8.3 5.9 5.3 5.7 2.6 7.9

6.7 8.3 7.4 4.7 8.1 8.8 8.8 8.0 7.4 5.8 6.5 8.4

3.5 6.9 4.7 5.9 6.3 7.6 9.3 7.7 7.2 8.1 9.2 8.4

Malta Lake (Poland); 2Cybina River (Poland); 3Baltic Sea (Poland); Paproć (Poland); nd – not detected. ⁎ average ± standard deviation (n = 6). Fig. 4. The chromatograms of blank river water and spiked river water extracted using the DES-UA-DLLME-SAP method. Sample was spiked with 5 ng mL−1 of each analytes: (1) 1-naphthylamine, (2) 2-chloroaniline and (3) 4-chloroaniline. Conditions: mobile phase - methanol/water at a ratio of 70/30 (v/v), a flow rate of 1.2 mL min−1 and detection at 240 nm;.

Table 4 Comparison of proposed the DES-UA-DLLME-SAP method and other DLLME methods used to the preconcentration of aromatic amines. Matrices

Analytes

Preconcentration method

Sample (volume)

pH

Extractant (volume)

Dispersive agent (volume/time)

LOD [ng mL1 ]

RSD [%]

Ref.

lake water, river water

4-toluidine 2-chloroaniline 4-chloroaniline 4-bromoaniline 2-nitroaniline 1-naphthylamine 2-chloroaniline 2-anilinoethanol 2-chloroaniline 4-bromo-N,Ndimethylaniline 2,4-dichloroaniline 1-naphthylamine 6-chloroaniline N,N-dimethylaniline aniline 4-toluidine 4-chloroaniline 4-anisidine 4-tert-butylaniline 2-chloroaniline 4-chloroaniline 1-naphthylamine

DLLME

5 mL

–

Tetrachloroethane (25 µL)

methanol (500 µL)

10 mL

12

Chlorobenzene (60 µL)

acetonitryle (500 µL)

IL-DLLME

10 mL

12

[BMIM][PF6] (100 µL)

methanol (750 µL)

4.1 5.3 4.8 5.0 9.7 7.2 6.3 3.7 4.7 3.3

[14]

DLLME

1.8 0.8 1.3 1.0 0.1 0.2 0.7 0.023 0.015 0.026

IL-UA-DLLME

10 mL

13

[HMIM][PF6] (60 µL)

ultrasounds (5 min)

DES-AA-DLLME-SFO

10 mL

11

ChCl:n-butyric acid (1:1) (65 µL)

air

DES-UA-DLLME-SAP

15 mL

12

[C14C6C6C6P]Cl:decanol (1:2) (40 µL)

ultrasounds (60 s)

0.49 0.17 0.46 0.27 3.0* 6.0* 1.8* 2.4* 5.3* 0.07 0.11 0.08

5.7 6.1 2.0 3.2 4.2 3.9 3.3 4.0 2.6 2.9 5.8 4.5

rainwater, melted snow water tap water, river water

melted snow water, river water, brook water tap water, surface water, river water, wastewater lake water, river water, sea water, melted snow water ⁎

[15] [35]

[36]

[27]

This study

[ng L-1]

correlation coefficients, precisions (RSD), recoveries, limits of detection (LODs), limits of quantitation (LOQs) and the preconcentration factor (PF) of this method. Each analyte (2-chloroaniline, 4-chloroaniline and 1-naphthylamine) exhibited good linearity with correlation coefficients (R2) ranging from 0.9975 to 0.9988. The LODs and LOQs were calculated on the basis of signal to noise (S/N) ratio. The S/N = 3 was used

for calculation of LOD and the S/N = 10 for calculation of LOQ. The LODs and LOQs were in the ranges of 0.07–0.11 ng mL−1 and 0.23–0.36 ng mL−1, respectively. The precisions (as RSDs) for six replicate measurements at three concentration levels (0.4, 5.0 and 40.0 ng mL−1) in a standard solution, under the optimal conditions, were in the range of 2.9–6.2%. PF was calculated as the ratio of the 5

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slopes of calibration curves for analytes before and after the preconcentration step, which were equal to 119, 116, and 121 for 2chloroaniline, 4-chloroaniline and 1-naphthylamine, respectively. The results were presented in Table 2.

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3.4. The analysis of the aqueous environmental samples The validated DES-UA-DLLME-SAP method was used for analysis of 2-chloroaniline, 4-chloroaniline and 1-naphthylamine in the aqueous environmental samples, i.e. lake water, river water, sea water and melted snow water. The results indicated that no aromatic amines were found in the samples. These samples were then spiked with 0.4, 5.0 and 40.0 ng mL−1 of each analyte in order to determine the recovery. The recoveries were in the range 85.1–99.9% with precisions of 2.6–9.3% (RSD). The results were presented in Table 3. The chromatogram of the aromatic amines in spiked river water was presented in Fig. 4. 3.5. Comparison of DES-UA-DLLME-SAP with other DLLME methods Comparison of the proposed DES-UA-DLLME-SAP method and the previously published DLLME methods used for the preconcentration of aromatic amines was presented in Table 4. The main novelty of the proposed method compared to other methods, is the use of a new, nontoxic, non-volatile deep eutectic solvent which consisted of trihexyl (tetradecyl)phosphonium chloride and decanol at a molar ratio of 1:2, instead of imidazolium ionic liquids or volatile organic solvents (i.e. tetrachloroethane, chlorobenzene). In addition, the use of ultrasound as a dispersing agent eliminates the use of toxic solvents, such as methanol or acetonitrile, in DLLME and significantly reduces the time of extraction. Also, the LODs of the proposed method are better than for other methods as well as the RSDs are comparable. All these results indicate that DES-UA-DLLME-SAP is a fast, sensitive and reproducible method that can be used for the preconcentration and determination of aromatic amines in water samples. 4. Conclusions In this study, a green and efficient DES-UA-DLLME-SAP method followed by HPLC-UV was developed for preconcentration and determination of aromatic amines in aqueous environmental samples. In the proposed method, a novel deep eutectic solvent (DES) characterized by low density was prepared by mixing trihexyl(tetradecyl)phosphonium chloride and decanol at a molar ratio of 1:2. Additionally, the use of DES, which is lighter than water and exhibits a much lower melting point than the melting point of water, allows for solidification of the aqueous phase after extraction and efficient collection of the sample from the surface of the DES phase for analysis. Ultrasounds were used to disperse the extractant in the aqueous phase of the sample. The modifications introduced in the proposed method allow to classify it as environmentally friendly. The DES-UA-DLLME-SAP/HPLC-UV method was successfully applied for determination of aromatic amines in aqueous environmental samples with good precision, quantitative recovery and high preconcentration factor. Declaration of Competing Interest There are no conflicts to declare. Acknowledgements This work was supported by the Polish Ministry of Science and Higher Education under Grant 03/31/SBAD/0382. 6

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