Electrodeposition of self-assembled poly(3,4-ethylenedioxythiophene) @gold nanoparticles on stainless steel wires for the headspace solid-phase microextraction and gas chromatographic determination of several polycyclic aromatic hydrocarbons

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Electrodeposition of self-assembled poly(3,4-ethylenedioxythiophene) @gold nanoparticles on stainless steel wires for the headspace solid-phase microextraction and gas chromatographic determination of several polycyclic aromatic hydrocarbons Liu Yang, Jie Zhang, Faqiong Zhao, Baizhao Zeng ∗ Key laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Science, Wuhan University, Wuhan, Hubei 430072, PR China

a r t i c l e

i n f o

Article history: Received 4 May 2016 Received in revised form 12 October 2016 Accepted 14 October 2016 Available online xxx Keywords: Solid phase microextraction Poly(3,4-ethylenedioxythiophene) Au nanoparticles Polycyclic aromatic hydrocarbons Electropolymerization

a b s t r a c t In this work, a novel poly(3,4-ethylenedioxythiophene)@Au nanoparticles (PEDOT@AuNPs) hybrid coating was prepared and characterized. Firstly, the monomer 3,4-ethylenedioxythiophene was selfassembled on AuNPs, and then electropolymerization was performed on a stainless steel wire by cyclic voltammetry. The obtained PEDOT@AuNPs coating was rough and showed cauliflower-like microstructure with thickness of ∼40 ␮m. It displayed high thermal stability (up to 330 ◦ C) and mechanical stability and could be used for at least 160 times of solid phase microextraction (SPME) without decrease of extraction performance. The coating exhibited high extraction capacity for some environmental pollutants (e.g. naphthalene, 2-methylnaphthalene, acenaphthene, fluorene and phenathrene) due to the hydrophobic interaction between the analytes and PEDOT and the additional physicochemical affinity between polycyclic aromatic hydrocarbons and AuNPs. Through coupling with GC detection, good linearity (correlation coefficients higher than 0.9894), wide linear range (0.01–100 ␮g L−1 ), low limits of detection (2.5–25 ng L−1 ) were achieved for these analytes. The reproducibility (defined as RSD) was 1.1–4.0% and 5.8–9.9% for single fiber (n = 5) and fiber-to-fiber (n = 5), respectively. The SPME-GC method was successfully applied for the determination of three real samples, and the recoveries for standards added were 89.9–106% for lake water, 95.7–112% for rain water and 93.2–109% for soil saturated water, respectively. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are a group of organic pollutants. In the environment they generally come from the incomplete combustion of organic materials and the sources include volcano, forest fire, industrial process, vehicle emission, refinery, incineration and burning tobacco [1]. PAHs exhibit significant hazard to the environment and human health as they have high toxicity, mutagencity and carcinogenicity. Especially, they are persistent and bioaccumulative, giving rising to their danger. In 2011, EU Regulation 835/2011 established the upper limits for a subset of four specific PAHs in various food matrices [2]. Owing to

∗ Corresponding author. E-mail address: [email protected] (B. Zeng).

the low contents of PAHs in the environmental matrix, enrichment is usually required before their detection. For their enrichment the most frequently employed technique is solid phase extraction (SPE), generally followed by GC/MS analysis [3–5]. For examples, molecularly imprinted polymers (MIPs) based SPE was used for the detection of PAHs in seawater [6,7]; stir bar sorptive extraction (SBSE) was employed to the analysis of PAHs in soil eluates [8]; air-assisted dispersive micro solid phase extraction (A-d␮-SPE) was applied for the detection of PAHs in biological samples [9]. Solid phase microextraction (SPME) has also been used for the analysis of PAHs [10–13], which is a sensitive technique and usually performed by using a polymer coated fiber [14–17]. But the available commercial fibers, such as polydimethylsiloxane (PDMS), polyacrylate (PA), and polydimethylsiloxane/divinylbenzen (PDMS/DVB), are moderately expensive and fragile, and have limited lifetime at high tempera-

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tures and in organic solvents. In addition, the variety of commercial fibers is rather limited and they lack high selectivity. For these reasons, many researchers focused on developing new fibers with better performance. In recent years, organic-inorganic hybrid materials have received considerable attention because they can combine the advantages of organic and inorganic materials to some extent [18,19]. Some hybrid materials, especially the hybrid nanomaterials, are considered to be high-efficiency sorbents due to their high specific surface area, and excellent thermal and mechanical stability [20–22]. For instance, Ali et al. prepared a polyaminithiophenol (PATP) with Au coating by layer-by-layer self-assembly for the extraction of PAHs in aqueous solution [23]. It showed excellent properties, but the layer-by-layer self-assembly process was cumbersome and time-consuming. Wu et al. fabricated a poly(3,4-ethylenedioxythiophene)-ionic liquid polymer functionalized multiwalled carbon nanotubes (PEDOT-PIL/MWCNTs) composite coating for the extraction of carbamate pesticides in apple and lettuce samples, which exhibited much higher sensitivity than commercial coatings [24]. In addition, for PEDOT the introduction of conductive nanomaterials benefited the control of its thickness and structure as its conductivity was poor and it tended to crack with its thickness increasing. As we all know, nanoparticles easily aggregate due to high surface energy, high adsorption etc, especially in organic media. PEDOT is one of the few electropolymers that present similar property and structure no matter whether prepared in neutral aqueous solution or in organic media. To the best of our knowledge, there are no reports about the preparation of gold nanoparticals (AuNPs) doped PEDOT coating through electrochemical method in aqueous solution. In this study, a poly(3,4-ethylenedioxythiophene)@AuNPs (PEDOT@AuNPs) hybrid coating was prepared. Firstly, the monomer 3,4-ethylenedioxythiophene (EDOT) was self-assembled on AuNPs, and then electropolymerization was performed on a stainless steel wire by cyclic voltammetry. The developed fiber demonstrated high selectivity toward PAHs due to hydrophobic interaction and the effect of AuNPs. The organic-inorganic hybrid coating was characterized and its extraction property was explored by using model analytes, including benzenes, phenols, amines and PAHs. The conditions were optimized for the extraction of PAHs, and environmental water samples were determined by coupling with GC.

2. Experimental 2.1. Reagents and materials All chemicals and reagents were of analytical grade. 3,4Ethylenedioxythiophene, 3-methylthiophene, 2,2 -bithiophene and chloroauric acid (HAuCl4 ·4H2 O) were purchased from Aladdin Chemistry Co., Ltd. (Shanghai, China). Trisodium citrate dehydrate (Na3 C6 H5 O7 ·2H2 O), sodium dodecylbenzenesulfonate (SDBS), sodium chloride (NaCl), potassium ferricyanide (K3 [Fe(CN)6 ]), potassium hexacyanoferrate(II) (K4 [Fe(CN)6 ]), potassium chloride (KCl), naphthalene (NAP), 2-methylnaphthalene (2-MNAP), acenaphthene (ACE), fluorene (FLU), phenanthrene (PHE), p-xylene, o-xylene, 1,3,5-trimethylbenzene, 1,4-dichlorobenzene, 1,3dichlorobenzene, o-cresol, p-cresol, m-4-xylenol, p-chlorophenol, aniline, N-methylaniline, m-methylaniline, o-chloroaniline, mchloroaniline, septas and vials came from the Reagent Factory of Shanghai. The stock solution of PAHs (0.10 mg mL−1 for all analytes) was prepared with absolute methanol and stored at −4 ◦ C. The water samples were lake water (Sample 1, from East Lake, Wuhan, China) and rain water (Sample 2), they were analyzed with-

out any other pretreatment process. Before determination the soil sample was pretreated according to previous report [25]. Briefly, the agricultural soil (1.0 g) was added to a glass bottle, and then 20 mL methanol was added. The bottle was capped and shaken for 24 h. After that, the turbid liquid was centrifuged for 10 min at 5000 rpm and the supernatant was collected for detection. 2.2. Instruments A CHI 617 A electrochemical workstation (CH Instrument Corp., Shanghai) was employed for preparing SPME fibers. A conventional three-electrode system was adopted, including a stainless steel wire working electrode (0.25 mm, OD), a Pt counter electrode (2.5 cm × 0.5 mm, OD) and a saturated calomel electrode (SCE) as reference electrode. Electrochemical impedance spectroscopy (EIS) experiment was carried out on a CHI 660 B electrochemical workstation (CH Instrument Corp., Shanghai). The solution used was 0.10 M KCl with 5.0 mM [Fe(CN)6 ]4− and 5.0 mM [Fe(CN)6 ]3− . Commercial SPME fiber (100 ␮m polydimethylsiloxane, PDMS) was supplied by Supelco (Bellefonte, PA, USA). The analysis of PAHs was performed on a Model SP-6890 gas chromatography instrument fitted with a flame ionization detection (FID) system and a splitless inlet liner (4.6 mm O.D. × 2.5 mm I.D. × 110 mm long) (Shandong Lunan Ruihong Chemical Instrument Co., Tengzhou, China). A N2000 chromatographic workstation program (Zhejiang University, Zhejiang, China) was used to process chromatographic data. The separation of samples was carried out on a SE-54 capillary column (30 m × 0.32 mm I.D.) with 0.5 ␮m film thickness (Lanzhou Atech Technologies, Lanzhou, China). The stationary phase was polydimethyl phenyl vinyl siloxane (containing 5% phenyl). The following column temperature program was used: 50 ◦ C held for 3 min, followed by increasing temperature to 200 ◦ C at a rate of 19 ◦ C min−1 , then at a rate of 4.5 ◦ C min−1 to 240 ◦ C, which was held for 2 min; finally it was programmed at 2 ◦ C min−1 to 250 ◦ C, which was held for 2 min. The total run time was 29 min. Hydrogen and air flow rates were maintained at 40 and 400 mL min−1 , respectively. Ultrapure nitrogen (99.999%, Xiangyun Chemical Co. Wuhan) was used as carrier gas at a constant flow rate of 1.0 mL min−1 . Purge flow rate of N2 was 8.1 mL min−1 and purge time was 45 s. The injection temperature was 280 ◦ C. Its inlet was operated under the splitless mode. The FID temperature was set at 280 ◦ C. The SPME device was laboratory-made. The scanning electron microscopy (SEM) images were obtained by using an LEO 1530 field emission SEM (Carl Zeiss NTS GmbH, Germany). Transmission electron microscopy (TEM) analysis was performed with a JEM-2100 (200 kV) electron microscopy. The energy dispersive spectroscopy (EDS) was recorded using a Quanta-200 SEM instrument (FEI, The Netherlands). 2.3. Preparation of PEDOT@AuNPs coating on stainless steel wire AuNPs (diameter: about 14 nm) were prepared by reducing HAuCl4 using citrate. Briefly, 200 mL 1.0 mM HAuCl4 solution was heated to boiling, subsequently, 5.0 mL 155 mM trisodium citrate solution was added quickly, resulting in the color changing from pale yellow to deep red. The solution was kept boiling for another 15 min and then cooled down to room temperature, and stored at 4 ◦ C. Fig. 1 shows the preparation process of the PEDOT@AuNPs fiber. Prior to electrodeposition, the stainless steel wire was treated with 1.0 M HNO3 , 1.0 M sodium hydroxide and distilled water each for 15 min, and then was dried at room temperature. AuNPs aqueous solution (0.50 mM, in terms of HAuCl4 ), EDOT (0.050 M) and SDBS (0.060 M) were mixed and let them self-assemble for 12 h. The PEDOT@AuNPs coating was electrodeposited on a stainless steel wire by using CV technique, which was performed between 0 V and

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SCE

Pt wire

Stainless wire electropolymerization

self-assembling

0 ~1.2 V, 50 mV S-1 25 scan cycles

12 h, 4 ° C

AuNP

O

SDBS

O O

S

EDOT

O

O

O

O

O

O

O

O S

S

Au

*

S

O

O

O

S

S

S

S

O

O S

S

S

O

O

O

*

S

O

O

O

n

O

O

Fig. 1. Schematic preparation process of PEDOT@AuNPs coating.

2.4. Extraction procedure A 10 mL aqueous solution was transferred into a 15 mL glass vial with PTFE septum. After adding 3.5 g NaCl, a magnetic stirring bar and 50 ␮g L−1 PAHs, the vial was tightly sealed with an aluminum cap to prevent sample loss, and then was put in a water bath. The magnetic stirrer was used to accelerate the extraction. When the temperature reached the fixed value, the fiber was exposed to the headspace over the stirred solution for fixed time. Then the fiber was withdrawn into the needle, removed from the sample vial and immediately introduced into the GC injector port for thermal desorption of 4 min. Each measurement was carried out in triplicate. The same procedure was adopted for the determination of samples. When the recoveries for the standards added were tested, 5.0 ␮L 5.0 mg L−1 PAHs solution was spiked in the water samples, while 5.0 ␮L 1.0 mg L−1 PAHs solution was spiked in the soil saturated extraction. 3. Results and discussion 3.1. Optimization of AuNPs concentration In order to achieve high extraction efficiency, several PEDOT@AuNPs fibers were prepared by varying the AuNPs

a.u.)

12 10 8

Peak area

1.2 V at a scan rate of 50 mV s−1 , and the number of scan cycle was set at 25. The total run time was 20 min. During the electrochemical polymerization, the surface of stainless steel wire gradually became black, indicating the formation of PEDOT@AuNPs film. The obtained fiber was kept in a desicator for 10 h at room temperature. After that, it was aged in an electric furnace at 100 ◦ C for 30 min and then at 280 ◦ C for 2 h under a gentle stream of N2 . The thickness of the coating, estimated by optical microscope, was about 40 ␮m. For comparison, a PEDOT fiber was also fabricated under the same conditions but without AuNPs, and a PEDOT/Au fiber was prepared by CV as described in previous publication with some modification [26]. Briefly, Au was electrodeposited on PEDOT coating by CV, the potential range was −0.2 V to −0.5 V, the scan rate was 20 mV s−1 , and the number of scan cycle was 10. In addition, EDOT was replaced by 3-methylthiophene (3-MPT) and 2,2 -bithiophene (BPT) to prepare poly(3-MPT)@AuNPs and poly(BPT)@ AuNPs coatings, respectively.

NAP 2-MNAP ACE FLU PHE

6 4 2 0 0

2/1

4/1

6/1

8/1 10/1 15/1 20/1

Ratio of AuNPs/EDOT Fig. 2. Influence of AuNP concentration on the extraction efficiency. Ratio of AuNPs and EDOT (mM/M): 2:1, 4:1, 6:1, 8:1; 10:1, 15:1, 20:1; EDOT concentration: 0.050 M; extraction time: 40 min; extraction temperature: 20 ◦ C; stirring rate: 600 rpm; NaCl concentration: 0.35 g mL−1 ; desorption time: 4 min; desorption temperature: 280 ◦ C, concentration of PAHs: 50 ␮g L−1 . Error bars show the standard deviation (n = 3).

concentration (i.e. HAuCl4 concentration, instead of AuNPs concentration), while the concentration of EDOT was kept unchanged (i.e. 0.050 M). When the concentration ratios (mM/M) of AuNPs and EDOT were 2/1, 4/1, 6/1, 8/1, 10/1, 15/1 and 20/1, the resulting fibers were denoted as PEDOT@AuNPs2/1, PEDOT@AuNPs-4/1, PEDOT@AuNPs-6/1, PEDOT@AuNPs-8/1, PEDOT@AuNPs-10/1, PEDOT@AuNPS-15/1, PEDOT@AuNPs-20/1, respectively. Their extraction efficiency is compared in Fig. 2. When the concentration of AuNPs was lower, the obtained PEDOT@AuNPs coating contained less AuNPs and the extraction efficiency was lower. However, when its concentration was too high the electropolymerization of EDOT became difficult, thus the extraction efficiency was also lower. When the ratio was 10/1 well-defined coating, with high extraction capacity, was achieved. The EIS of PEDOT and PEDOT@AuNPs coatings were shown in Fig. S1. The semicircle part at higher frequencies reflected its electron-transfer limited process and the linear portion at lower frequencies corresponded to the diffusion-limited process. The semicircle diameter indicated the charge transfer resistance (Rct ) [27]. Here the Rct value of PEDOT coating was about 53,220 , while

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polymer. This indicated that the obtained PEDOT@AuNPs coating was stable below 330 ◦ C, which was similar to that of PEDOT coating. It meant that AuNPs hardly influenced the thermal stability of PEDOT in this case.

that of PEDOT@AuNPs was about 7940 . Therefore, it was easier to regulate the PEDOT thickness in the presence of AuNPs.

3.2.2. Morphology The surface morphology of the PEDOT@AuNPs fiber is displayed in Fig. 4. As can be seen, the PEDOT@AuNPs coating is rough and has cauliflower-like micro-structure. The AuNPs are uniform and their diameters are about 14 nm. As shown in Fig. S2, the size of AuNPs in PEDOT/AuNPs is different from that in PEDOT@AuNPs, and the later is more uniform. Furthermore, the PEDOT/AuNPs coating presents cracks (Fig. S3). The SEM images of poly(3-MPT)@AuNPs, poly(BPT)@AuNPs and PEDOT@AuNPs fibers are compared in Fig. S4. The poly(3-MPT)@AuNPs and poly(BPT)@AuNPs coatings are not uniform. In addition, they demonstrate poor electropolymerization behavior, and the coatings are easy to exfoliate. The EDS spectrum of the PEDOT@AuNPs coating is also recorded (Fig. S5), the peak at 2.12 keV, assigned to gold, is almost overlapped by the peak of sulfur, meaning that the content of AuNPs is low.

3.2. Characterization of PEDOT@AuNPs coating

3.3. Optimization of SPME parameters

3.2.1. Thermal stability The thermal stability of PEDOT@AuNPs coating was studied by recording the chromatograms of a blank PEDOT@AuNPs fiber at different desorption temperatures (i.e. from 280 ◦ C to 340 ◦ C) (Fig. 3). When the temperature was higher than 330 ◦ C, some chromatographic peaks occurred due to the thermal decomposition of the

3.3.1. Extraction temperature The effect of extraction temperature on the extraction efficiency was examined from 10 ◦ C to 50 ◦ C. As shown in Fig. S6, higher extraction efficiency was observed around 20 ◦ C for the five PAHs. As we know, elevated temperature is favorable for the diffusion of analytes from bulk phase to the coating and can facilitate the extrac-

Fig. 3. Blank chromatograms for the PEDOT@AuNPs fiber desorbed at different temperatures.

Fig. 4. SEM images of PEDOT@AuNPs fiber (a, c), the cross-section image of PEDOT@AuNPs fiber (b) and TEM image of PEDOT@AuNPs (d).

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tion equilibrium. On the contrary, with increasing temperature the distribution coefficient of analyte in the coating decreases because surface adsorption is generally an exothermic process. Here low temperature is favorable for the SPME, probably due to the exothermic effect. Hence, 20 ◦ C was adopted for subsequent experiments.

10 8

5

PEDOT PEDOT/AuNPs PDMS PEDOT@AuNPs

6

3.3.2. Extraction time Extraction time is another major parameter affecting extraction efficiency. SPME is an equilibrium-based technique and there is a direct relationship between the extracted amount and the extraction time. Here the effect of extraction time on the extraction efficiency was tested from 10 to 50 min (Fig. S7). As a result, all compounds reached extraction equilibrium around 40 min and further extending time led to slight decrease. Thus 40 min was chosen as the extraction time. 3.3.3. Stirring rate The influence of stirring rate on extraction efficiency was also investigated. Generally, stirring accelerates mass transfer of target molecules from bulk solution to the coating. As shown in Fig. S8, the extraction efficiency increased with stirring rate changing from 400 to 600 rpm. However, when it was above 600 rpm the rotating of magnetic stirring bar was not very balanced, leading to the decrease of extraction efficiency. Therefore, stirring rate was fixed at 600 rpm in the experiments.

4 2 0 NAP

2-MNAP

ACE

3.3.5. Desorption time To examine the release of the extracted analytes in the GC injector port, desorption time was changed from 2 min to 5 min. Result revealed that the peak areas for the five PAHs increased with increasing desorption time up to 4 min at 280 ◦ C, then they kept almost constant (Fig. S10). Therefore, 4 min was sufficient for the analytes to desorb from the PEDOT@AuNPs fiber at this temperature. 3.4. Comparison of different fibers The extraction efficiency of PEDOT fiber, PEDOT@AuNPs fiber, PEDOT/Au and commercial PDMS fibers was compared under their optimized conditions (Figs. S11–S13). As can be seen in Fig. 5, the extraction efficiency of the PEDOT@AuNPs fiber is 2–15 times as high as that of PEDOT, PEDOT/Au and PDMS fibers. In addition, the distribution constants of PAHs between coating and liquid phase (Kfs ) were calculated (Table S1) [28]. The result showed that the Kfs values for PEDOT@AuNPs coating were 2–3 times of those of other coatings, meaning that it had stronger adsorption ability. Furthermore, a significant trend was noticed that the adsorption affinity increased with the number of condensed ring of PAHs increasing and their hydrophobicity rising (Kow , Table S2). This can be attributed to the hydrophobic interaction between PAHs and PEDOT coating plus the physicochemical affinity between PAHs and AuNPs. The affinity may be related to the electron transference between PAHs (␲-donor system) and AuNPs [29]. 3.5. Method evaluation The characteristic parameters of this PEDOT@AuNPs coating for analytical application were determined and listed in Table 1. The

PHE

Fig. 5. Comparison of the extraction efficiency of PEDOT/AuNPs, PEDOT, PDMS (coating thickness: 100 ␮m) and PEDOT@AuNPs fibers for PAHs under their optimized conditions. Concentration of PAHs: 50 ␮g L−1 . Error bars show the standard deviation (n = 3).

10 8

a: p-xylene

k: N-methylaniline

b: o-xylene

l: m-methylaniline

c: 1,3,5-trimethylbenzene

m: o-chloroaniline

d: 1,4-dichlorobenzene

n: o: p: q: r: s:

e: 1,3-dichlorobenzene f: o-cresol g: p-cresol

6

h: m-4-xylenol i: p-chlorophenol

3.3.4. Salt concentration Fig. S9 showed the influence of NaCl concentration on the extraction efficiency of the fiber. For these PAHs, the extraction amounts increased as ionic strength increased, and they reached the highest values around 0.35 g mL−1 . Thus saturated NaCl solution was selected in the experiments.

FLU

4

k

l

n o

j

h a b cd e

f

benzenes

phenols

g

q

m-chloroaniline naphthalene 2-methylnaphthalene acenaphthene fluorene phenanthrene

j: aniline

2 0

rs

p

m

i amines

PAHs

Fig. 6. Comparison of the extraction efficiency of PEDOT@AuNPs fiber for benzenes, phenols, amines and PAHs.

linear ranges were 0.01 ␮g L−1 –100 ␮g L−1 , with correlation coefficients of 0.9894–0.9985. The detection limits (LODs) of the PAHs were estimated to be 2.5 ng L−1 –25 ng L−1 , based on a signal-tonoise ratio of 3 (S/N = 3) [30]. The relative standard deviations (RSDs) for the intra-fiber were 1.1%-4.0% (n = 5), while for the inter-fiber (four fibers, 3 replicates each) the RSDs were <9.9% for 50 ␮g L−1 PAHs. As could be seen in Table 2, this method was quite good in comparison with other methods in terms of linear range, LOD and repeatability. In addition, the PEDOT@AuNPs fiber showed high durability (Fig. S14). After it underwent 160 adsortion/desorption cycles, its extraction efficiency was almost unchanged. This was related to the high stability and mechanical strength of PEDOT@AuNPs coating. 3.6. Extraction selectivity of PEDOT@AuNPs fiber Four series of organic compounds, including benzenes (i.e. p-xylene, o-xylene, m-trimethylbenzene, p-dichlorobenzene, o-dichlorobenzene), phenols (i.e. o-cresol, p-cresol, m-4-xylenol, p-chlorophenol), amines (i.e. aniline, N-methylaniline, mmethylaniline, o-chloroaniline, m-chloroaniline) and polycyclic aromatic hydrocarbons (i.e. naphthalene, 2-methylnaphthalene, acenaphthene, fluorene, phenanthrene) were chosen to test the extraction selectivity of the PEDOT@AuNPs fiber. The results were shown in Fig. 6, the novel SPME fiber did not suit for the extraction of benzenes and phenols no matter what extraction conditions were used, but it presented good enrichment effect for polycyclic aromatic hydrocarbons. Under the same extraction conditions, the extraction efficiency of amines was lower than that of PAHs. As

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Table 1 Analytical parameters for PAHs measured with PEDOT@AuNPs fiber based HS-SPME-GC method. LOD (ng L−1 )

Analytes

Linear range (␮g L−1 )

Regression equation

Correlation coefficient

RSD(%) One fiber

Fiber-to-fiber

n=5

n=5

NAP

25

0.1–2.5 2.5–100

y = 1233x + 944.8a y = 6261x − 3004

0.9925 0.9985

3.8

9.9

2-MNAP

25

0.1–2.5 2.5–100

y = 1004x + 625.1 y = 8683x − 13734

0.9905 0.9894

2.7

8.2

ACE

10

0.025–2.5 2.5–100

y = 1859x + 330.1 y = 15620x − 44690

0.9960 0.9905

1.5

8.2

FLU

5.0

0.025–2.5 2.5–100

y = 1928x + 1067 y = 20580x − 40373

0.9899 0.9925

1.1

5.8

PHE

2.5

0.01–0.5 0.5–100

y = 3635x + 834.3 y = 20620x − 42948

0.9925 0.9970

4.0

9.7

a

y: peak area; x: concentration (␮g L−1 ).

Table 2 Comparison of analytical data of the proposed method with other reported methods. Methods a

PEDOT/GO-GC-FID AuNPs-GC-FID AuNPs-HPLC-UVb PEDOT@AuNPs-GC-FID a b

Linear ranges (␮g L−1 )

LOD (␮g L−1 )

RSD (%)

Ref

0.40–600 0.050–300 0.050–300 0.01–100

0.050−0.13 0.025−0.25 0.0080−0.037 0.0025−0.025

9.8–13 2.5–7.9 3.5–9.3 1.1–4.0

[31] [29] [32] present method

GO, graphene oxide. HPLC-UV, high-performance liquid chromatography with UV detection.

4

5

Table 3 GC-FID determination results of PAHs in water samples after HS-SPME with PEDOT@AuNPs fiber.

5

3

Signal (mV)

4

1 2

3

a

2

5

1 3

0

Samples

Analytes

Found (␮g L−1 )

Recovery (%)a

Lake water

NAP 2-MNAP ACE FLU PHE

ndc nd nd nd 0.084

106 ± 4.8b 99.3 ± 4.8 89.9 ± 7.1 98.1 ± 1.2 97.8 ± 5.2

Rain water

NAP 2-MNAP ACE FLU PHE

nd nd 0.52 nd nd

99.8 ± 0.5 97.7 ± 6.4 112 ± 8.1 98.0 ± 9.6 95.7 ± 6.7

Soil saturated extraction

NAP 2-MNAP ACE FLU PHE

nd nd nd nd nd

97.37 ± 2.2 95.5 ± 2.4 105 ± 1.8 109 ± 3.7 93.2 ± 9.9

b c

-1 0

5

10

15

20

25

Time (min) Fig. 7. Typical chromatograms of 2.5 ␮g L−1 standard solution (a), lake water (b) and rain water (c) after extracted with the PEDOT@AuNPs coating, followed by GC-FID analysis. Other conditions are the same as in Fig. 2.

to this, it could be ascribed to the additional interaction between PAHs and AuNPs surface [29]. In theoretical and computational chemistry, gold is considered “anomalous” due to its very large relativistic effects [33]. The relativistic effects lead to excellent electronic mobility, which makes it easy to form coordinate bond (to use its empty valency shell) with atoms having long pair electrons or to form feedback-coordinate bond (use occupational therapists valency electrons) with atoms having unoccupied orbital. PAHs have larger ␲-system and thus the interaction between PAHs and AuNPs is stronger. Furthermore, there may be electron transference between PAHs (␲-donor system) and AuNPs. 3.7. Application The method was applied to the determination of PAHs in water and soil samples. The typical chromatograms for water samples were shown in Fig. 7, and the quantification results were listed in Table 3. As could be seen, the concentrations of PHE and ACE

a Recovery for spiked PAHs solutions. Spiked level: 2.5 ␮g L−1 (for lake water and rain water samples), and 0.50 ␮g L−1 (for soil extractant). b Mean values ± standard deviations. c Not detected.

were ca. 0.084 ␮g L−1 and 0.52 ␮g L−1 for lake water and rain water, respectively, while the concentration of other PAHs were below the LODs. When the water samples were spiked with analytes at 2.5 ␮g L−1 level, the mean recoveries were 89.9%–112% and the RSDs were 1.2%–9.6%. No PAHs were found in soil samples, and the recoveries for spiked analytes (0.50 ␮g L−1 ) ranged from 93.2% to 109%. These demonstrated that the method was reliable and suitable for the selective preconcentration and sensitive determination of the target anlaytes in environmental samples. 4. Conclusions In summary, self-assembled AuNPs@EDOT was electropolymerized on a stainless steel wire as SPME coating. It presented

Please cite this article in press as: L. Yang, et al., Electrodeposition of self-assembled poly(3,4-ethylenedioxythiophene) @gold nanoparticles on stainless steel wires for the headspace solid-phase microextraction and gas chromatographic determination of several polycyclic aromatic hydrocarbons, J. Chromatogr. A (2016), http://dx.doi.org/10.1016/j.chroma.2016.10.041

G Model CHROMA-357989; No. of Pages 7

ARTICLE IN PRESS L. Yang et al. / J. Chromatogr. A xxx (2016) xxx–xxx

cauliflower-like micro-structure and had plentiful access sites for the adsorption of target analytes. Owing to the synergetic effect of hydrophobic PEDOT and AuNPs, the PEDOT@AuNPs coating exhibited high extraction efficiency and good selectivity for PAHs. Besides that, the PEDOT@AuNPs coating displayed good durable property (could be used for more than 160 times) and reproducibility. Coupled with GC, the PEDOT@AuNPs based fiber could be used for the determination of PAHs in environmental samples. Acknowledgement The authors appreciate the support of the National Natural Science Foundation of China (Grant No. 21275112). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chroma.2016.10. 041. References [1] H.C. Menezes, Z. de Lourdes Cardeal, Determination of polycyclic aromatic hydrocarbons from ambient air particulate matter using a cold fiber solid phase microextraction gas chromatography–mass spectrometry method, J. Chromatogr. A 1218 (2011) 3300–3305. [2] The European Commission, Off. J. Eur. Union 215 (2011) 4–8. [3] S.R. Anna, Determination of polycyclic aromatic hydrocarbons in coffee and coffee substitutes using dispersive SPE and gas chromatography-mass spectrometry, Food Anal. Methods 8 (2015) 109–121. [4] J. Pincemaille, C. Schummer, E. Heinen, G. Moris, Determination of polycyclic aromatic hydrocarbons in smoked and non-smoked black teas and tea infusions, Food Chem. 154 (2014) 807–813. [5] C.E. Ramirez, C.T. Wang, P.R. Gardinali, Fully automated trace level determination of parent and alkylated PAHs in environmental waters by online SPE-LC-APPI-MS/MS, Anal. Bioanal. Chem. 406 (2014) 329–344. [6] M. Serrano, M. Bartolome, A. Gallego-Pico, R.M. Garcinuno, J.C. Baravo, P. Fernandez, Synthesis of a molecularly imprinted polymer for the isolation of 1-hydroxypyrene in human urine, Talanta 143 (2015) 71–76. [7] W.L. Ho, Y.Y. Liu, T.C. Lin, Development of molecular imprinted polymer for selective adsorption of benz[a]pyrene among airborne polycyclic aromatic hydrocarbon compounds, Environ. Eng. Sci. 28 (2011) 421–434. [8] O. Krüger, G. Christoph, U. Kalbe, W. Berger, Comparison of stir bar sorptive extraction (SBSE) and liquid–liquid extraction (LLE) for the analysis of polycyclic aromatic hydrocarbons (PAHs) in complex aqueous matrices, Talanta 85 (2011) 1428–1434. [9] M. Rajabi, A.G. Moghadam, B. Barfi, A. Asghari, Air-assisted dispersive micro-solid phase extraction of polycyclic aromatic hydrocarbons using a magnetic graphitic carbon nitride nanocomposite, Microchim. Acta 183 (2016) 1449–1458. [10] A. Kremser, M.A. Jochmann, T.C. Schmidt, PAL SPME Arrow–evaluation of a novel solid-phase microextraction device for freely dissolved PAHs in water, Anal. Bioanal. Chem. 408 (2016) 943–952. [11] M.X. Gu, Z.Q. Gong, G. Allinson, P.D. Tai, R.H. Miao, X.J. Li, C.Y. Ji, J. Zhuang, Variations in the bioavailability of polycyclic aromatic hydrocarbons in industrial and agricultural soils after bioremediation, Chemosphere 144 (2016) 1513–1520. [12] X. Zhang, X.H. Zang, J.T. Wang, C. Wang, Q.H. Wu, Z. Wang, Porous carbon derived from aluminum-based metal organic framework as a fiber coating for the solid-phase microextraction of polycyclic aromatic hydrocarbons from water and soil, Microchim. Acta 182 (2015) 2353–2359. [13] K.A. Maruya, W.J. Lao, D. Tsukada, D.W. Diehl, A passive sampler based on solid phase microextraction (SPME) for sediment-associated organic pollutants: comparing freely-dissolved concentration with bioaccumulation, Chemosphere 137 (2015) 192–197.

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Please cite this article in press as: L. Yang, et al., Electrodeposition of self-assembled poly(3,4-ethylenedioxythiophene) @gold nanoparticles on stainless steel wires for the headspace solid-phase microextraction and gas chromatographic determination of several polycyclic aromatic hydrocarbons, J. Chromatogr. A (2016), http://dx.doi.org/10.1016/j.chroma.2016.10.041