Role of Fe(III) in preventing humic interference during As(III) detection on gold electrode: Spectroscopic and voltammetric evidence

Journal of Hazardous Materials 267 (2014) 153–160

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Role of Fe(III) in preventing humic interference during As(III) detection on gold electrode: Spectroscopic and voltammetric evidence Zhong-Gang Liu a,b,1 , Xing Chen a,1 , Yong Jia a , Jin-Huai Liu a , Xing-Jiu Huang a,b,∗ a b

Nanomaterials and Environmental Detection Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, PR China Department of Chemistry, University of Science and Technology of China, Hefei 230026, PR China

h i g h l i g h t s

g r a p h i c a l

a b s t r a c t

• Humic acids interfere with the voltammetric detection of As(III) on gold electrode through adsorption and possible complexation. • Addition of Fe(III) removes this interference and helps in the electroanalytical detection of As(III). • FTIR and XPS studies suggest that the formation of Fe(III)–HA complex prevents adsorption of HA on gold and limits As–HA complex formation.

a r t i c l e

i n f o

Article history: Received 21 September 2013 Received in revised form 30 November 2013 Accepted 18 December 2013 Available online 3 January 2014 Keywords: As(III) detection Influence of HA and Fe(III) Stripping voltammetry FTIR XPS

a b s t r a c t A drawback of As(III) detection using square wave anodic stripping voltammetry (SWASV) is that it is susceptible to interferences from various metals or organic compounds, especially in real sample water. This study attempts to understand the interference of co-existing of Fe(III) and humic acid (HA) molecules to the electrochemical detection of As(III) using Fourier transform infrared (FTIR) spectrum and X-ray photoelectron spectroscopy (XPS). The electrochemical experiments include stripping of As(III) in the solutions containing HA with different concentrations, cyclic voltammetry in 0.5 M H2 SO4 in the presence of HA or Fe(III) with/without addition of Fe(III) or HA, and stripping of As(III) in the presence of HA or Fe(III) with/without addition of Fe(III) or HA. FTIR and XPS are employed to confirm the affinity of HA to Fe(III) or As(III) in acidic condition. © 2014 Elsevier B.V. All rights reserved.

1. Introduction The contamination of arsenic in groundwater is now regarded as a serious worldwide threat to human health in scores of regions

∗ Corresponding author at: Nanomaterials and Environmental Detection Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, PR China. Tel.: +86 551 6559 1167; fax: +86 551 6559 2420. E-mail address: [email protected] (X.-J. Huang). 1 These two authors contributed equally to this work. 0304-3894/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2013.12.054

and countries and has been described as “the largest poisoning of a population in history” by the World Health Organization (WHO) [1,2]. Long period drinking of such arsenic polluted groundwater could cause many chronic arsenicosis type of diseases, such as “blackfoot” disease, atherosclerosis, hyperkeratosis, cerebrovascular disease, lung cancer and skin cancers [2–4]. Thus, the research on detecting and monitoring such a pollutant source has been extensively developed. In a number of proposed analytical methods [5–7], electrochemical technique has been developed recently considering its excellent properties, such as highly sensitive, easy to perform, and low-cost [8–10]. For example, Compton et al. reported

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detection of arsenic(III) using gold nanoparticle-modified electrode, gold nanoparticles modified glassy carbon microspheres with carbon nanotubes wiring, and sonically assisted method [11–13]. Raj et al. obtained an excellent sensitivity (3.14 ␮A ppb−1 ) toward arsenic using gold nanoelectrode ensembles [14]. Ohsaka et al. demonstrated that the Au(111)-like polycrystalline gold electrode is favorable for the selective detection of As(III) [15]. Luong et al. realized the electrochemical determination of arsenite using a gold nanoparticle modified glassy carbon electrode and flow analysis, reusable platinum nanoparticle modified boron doped diamond microelectrodes, and arsenite oxidase and multiwalled carbon nanotube modified electrodes [16–18]. Swain et al. developed a method for total inorganic arsenic analysis using Au-coated, diamond thin-film electrode [19]. Kounaves et al. reported on-site analysis of arsenic in groundwater using a microfabricated gold ultramicroelectrode array [20]. Besides, a Prussian blue-modified screen-printed electrode, multiwalled carbon nanotube chemically modified gold electrode, iridium-implanted boron-doped diamond electrodes, etc., have also been reported for the analysis of arsenite [21,22]. Very recently, we reported to use Fe3 O4 -RTIL(room temperature ion liquids) composite modified screen-printed carbon electrode for the detection of As(III) [23]. It can be seen that the attention of these researches concentrated on the finding of new sensing interfaces for analyzing simple water samples. However, the component of environmental groundwater is so complicated. It includes various metal ions and organic compounds. A series of important works by Berg’s group, who studied the voltammetric determination of arsenic in natural groundwater or seawater [24–30]. Similar work was done by Smart and co-workers [31]. It is noted that only electrochemical results were shown under different conditions, including the influence of pH, dissolved oxygen, various metals and organic compounds, etc., on the results. It is necessary to point out that, one of the natural organic matters, humic acid (HA), as a ubiquitous species in aquatic systems, is recognized as an intractable issue and has a serious interference on the accurate and efficient detection of arsenic, thus limiting the practical application of electrochemical technique in groundwater or complicated conditions. It has been verified that As-contaminated groundwater at Togtoh, Inner Mongolia, China contains high concentrations of HA (about 22,000 ␮g L−1 ). Currently, the interference of HA, fulvic acids, and surfactants on the electrochemical behavior of As(III) is being concerned. The researchers found that obvious interference can be caused by HA on the electrochemical response of As(III) [24,26,27,29]. They suggested that the interference might be due to a surfactant effect or the formation of poorly reversible complex. Song and co-workers ascribed the decrease in response of As(III) to that Au foil electrode was more easy to fouling by HA than that of Au-coated diamond electrode [32]. From these literatures, it is hard to find a discussion about how HA or other metal ions affect the electrochemical response of As(III). As described earlier, besides organic compounds, various metal ions, such as Fe(III), Mn(II), Pb(II), Zn(II), Cu(II), and Hg(II) are widely distributed in groundwater. Furthermore, it has been demonstrated that metal ions could bind with HA. Based on this fact and the results reported previously, the research on the electrochemical response of As(III) under the co-existence of HA and metal ions should be of great significance. In the present work, we attempt to understand the impact of HA and metal ions (e.g., Fe(III)) on the electrochemical response of As(III) using Fourier transform infrared (FTIR) spectrum and X-ray photoelectron spectroscopy (XPS). This assessment aims to investigate how existence of Fe(III) affects the interference of HA on electrochemical response toward As(III). As-contaminated groundwater at Xing Wang Zhuang, Togtoh, Inner Mongolia, China, which is rich in HA and metal ions, was selected as research background water. Fe(III) was selected as a representative metal ion which is

based on two parts, involving that (1) Fe(III) and HA, commonly associated in natural water and its amount (300 ␮g L−1 ), are much higher than other metal ions and (2) Fe(III) has a stronger binding ability than others (Pb(II), Zn(II), Cu(II), etc.) at low pH. The results will provide important insights into the broad impacts of organic compounds and metal ions on As(III) determination. 2. Experimental and methods 2.1. Chemicals and reagents All reagents were of analytical-grade and used as received. A 1000 mg L−1 As(III) stock solution was purchased from Shanghai Canspec Scientific Instruments Co., Ltd. (China) and wrapped to prevent oxidation by light. Non-acidified standard solutions with concentrations of 10 mg L−1 As(III) were prepared daily. 200 mg L−1 Fe(III) was prepared by dissolving Fe(NO3 )3 in deionized water. Humic acid (HA) was purchased from Shanghai Yixin Chemical Reagent Co., Ltd., China. HA was primarily composed of fulvic acid (FA) and similar to that existed in Togtoh water (Fig. S1, Supporting information). This is verified by UV–vis spectroscopy with absorption peak at 254 nm (Fig. S2). HA stock solution (1000 mg L−1 ) was prepared by dissolving 0.1 g solid HA in 100 mL deionized water. 0.038 M N2 H4 ·2HCl electrolyte was prepared by mixing 15 mL of 12 M HCl and 2.0 g N2 H4 ·2HCl to a final volume of 500 mL (pH 0.5). Note that N2 H4 ·2HCl used as an electrolyte is based on two parts. (1) N2 H4 ·2HCl, as an antioxidant, would avoid or restrain the oxidation of As(III) to As(V) caused by the oxidant HOCl, the latter derives from the oxidation of chloride in the deposition process [27,33]. (2) The strong reducing property of N2 H4 ·2HCl would lead to the reduction of As(III) to As(0) in the deposition process [34,35]. Ultrapure fresh water was obtained from a Millipore water purification system (MilliQ, specific resistivity > 18 M cm, S.A., Molsheim, France) and used in all runs. 2.2. Instrumentation Electrochemical experiments were recorded using an AutoLab computer-controlled potentiostat (Eco Chemie, Utrecht, Netherlands) associated with the GPES software. A 10 mL glass cell was used containing Au microwire electrode (12.7-␮m diameter, 1-mm length), an Ag/AgCl as reference electrode and a platinum wire as counter electrode. Fourier transform infrared (FTIR) spectrum was recorded in an IR-440 spectrometry (Shimadzu, Japan). X-ray photoelectron spectroscopy (XPS) analyses of the samples were conducted on a VG ESCALAB MKII spectrometer using a Mg K␣ X-ray source (1253.6 eV, 120 W) at a constant analyzer. UV–vis spectrum was measured with a UV 2550 spectrophotometer (Shimadzu, Japan). The pH value was measured using pH meter (Model: PHS-3C). 2.3. Electrochemical measurements Au microwire electrode was conditioned daily by cyclic voltammetry (CV) between −0.2 and 1.5 V for 10 cycles at a scan rate of 100 mV s−1 in 0.5 M H2 SO4 . The reduction peak area of the gold oxide was used to check that the roughness of the gold surface was constant during the experiments. Electrochemical measurements were carried out using square wave anodic stripping voltammetry (SWASV) mode for As(III) detection in 0.038 M N2 H4 ·2HCl electrolyte (pH 0.5). A deposition potential of −0.35 V was applied for 90 s to the working electrode with stirring (600 rpm). The SWASV responses were recorded between −0.2 and 0.6 V with step potential of 5 mV, amplitude of 20 mV and frequency of 50 Hz. A desorption potential of 0.6 V for 20 s was performed for conditioning the microelectrode under stirring

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conditions (600 rpm). All experiments were performed at room temperature. 2.4. Sample preparation for FTIR and XPS analysis Samples (HA, HA–As, HA–Fe, HA–As–Fe) were prepared in batch experiments in 0.038 M N2 H4 ·2HCl solution (pH 0.5) and carried out at 298 K in 9 mL polyethylene centrifuge tube for 24 h in order to realize a complete complex between HA and Fe(III) or As(III). The samples were centrifuged and washed with deionized water for several times to remove the residual ions (Fe(III), As(III)), and then the products were dried in a vacuum oven at 60 ◦ C for 10 h. 3. Results and discussion 3.1. Stripping response of As(III) in the presence of HA The electrochemical response of As(III) interfered with different concentrations of HA was firstly evaluated, as shown in Fig. 1. The experiments were realized by immersing Au microwire electrode into the N2 H4 ·2HCl solution containing different HA concentrations for 20 min and then transferring to another N2 H4 ·2HCl solution for electrochemical detection of As(III). It can be found that stripping responses of As(III) gradually decrease when increasing the HA concentrations up to 40 mg L−1 . For example, after addition of 20 mg L−1 HA, the responses of 10, 20, 40, 60, and 80 ␮g L−1 As(III) at Au microwire electrode were decreased by 24.4%, 16.6%, 11.6%, 10.4% and 8.1%, respectively. When 40 mg L−1 HA is used, the corresponding responses of As(III) were decreased by 41.8%, 33.6%, 22.4%, 20.4% and 15.5%, respectively. This indicates that the HA molecules directly interact with electrode surface, resulting in the responses decrease of As(III). Note that no obvious change in the stripping peak potential as well as peak shape (half-width) with the addition of HA has been observed (Fig. 1b). Some potential reasons may be involved. (1) No complexation between HA and As(III) is taking place; (2) the complex kinetics are much slow with the lower diffusion coefficients, only leading to the decrease in stripping signal; (3) the complexation between As(III) and HA is occurring but would be predicted to be weak, especially at the low pH [36], which is recognized as acceptable and followed investigation was carried out. In addition, it is worth pointing out that the change in stripping peak current of As(III) is perfectly consistent with that in stripping peak charge (Fig. 1c). In detail, the aromatic groups and oxygen-containing groups of HA are capable of adsorbing on the surface of Au microwire electrode through the “end on” configuration or single “bridge” and the bidentate bonding of COO− [37], as this has a direct interference on the electrochemically active area of electrode. Moreover, Au microwire electrode before and after immersing in the N2 H4 ·2HCl solution containing 200 mg L−1 HA was characterized by scanning electron microscopy (SEM) (Fig. S3, Supporting information). In contrast to the pristine Au microwire electrode, some dark spots can be apparently observed on the electrode surface after immersing in HA solution. It also demonstrates that HA molecules can interact with Au microwire electrode surface through adsorption or adhesion, thus masking the efficient binding sites to some extent, and resulting in the decrease of electrochemical active area. 3.2. Cyclic voltammetry of HA and Fe(III) system Fig. 2a shows the effect of HA concentrations ranging from 0 to 40 mg L−1 on the electrochemical performance of Au microwire electrode in 0.5 M H2 SO4 in the presence of Fe(III). Cyclic voltammetry (CV) was employed and its changes in reduction peak and its changes in reduction peak currents at approximately +0.90 V were recorded. As seen from Fig. 2a, in the absence of Fe(III), the peak

Fig. 1. (a) Dependence of stripping current of As(III) on the concentration of HA. (b) Typical stripping voltammograms of 20 ␮g L−1 As(III) without (red line) and with HA (ranging from 10 to 40 mg L−1 ) (black lines). The dotted line refers to the baseline. (c) Dependence of stripping current and corresponding peak charge of 20 ␮g L−1 As(III) on the concentration of HA. Electrolyte, N2 H4 ·2HCl solution (pH 0.5); deposition potential, −0.35 V; deposition time, 90 s; conditioning potential, 0.6 V; conditioning time, 20 s; step potential, 5 mV; amplitude, 20 mV; frequency, 50 Hz. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

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Fig. 2. (a) Dependence of cyclic voltammetric current (at +0.90 V) in 0.5 M H2 SO4 on the concentration of HA with/without Fe(III). (b) Dependence of cyclic voltammetric current (at +0.90 V) in 0.5 M H2 SO4 on the concentration of Fe(III) with/without HA. Scan rate: 100 mV s−1 .

currents gradually decrease along with increasing the HA concentrations. With addition of 20 and 40 mg L−1 HA, the peak current decreases by 7.8% and 13.8%, respectively. However, in the presence of 20 mg L−1 Fe(III), 4.3% and 7.5% decrease in the peak currents are observed when 20 mg L−1 and 40 mg L−1 HA are added, respectively. Interestingly, when 40 mg L−1 Fe(III) is contained, only 0.2% and 0.4% can be observed, respectively. The results reveal that Fe(III) can bind to the added HA molecules, thus blocking the interaction between electrode surface and HA, consequently resulting in a constant peak current. On the contrary, cyclic voltammetry in 0.5 M H2 SO4 was carried out under different Fe(III) concentrations

ranging from 0 to 40 mg L−1 in the presence of 0, 20, and 40 mg L−1 HA. The currents at +0.90 V were collected and are shown in Fig. 2b. In the absence of HA, no apparent change is observed and the relative standard deviation (RSD) is 1.1%. This indicates that Fe(III) has no influence on the electrochemical performance at Au microwire electrode. Furthermore, no redox peak of Fe(III) is observed in the cyclic voltammogram (data not shown), suggesting that redox reaction of Fe(III) does not occur at Au microwire electrode. When 20 mg L−1 and 40 mg L−1 HA are added into 0.5 M H2 SO4 (without Fe(III)), respectively, a decrease of 4.1% and 5.8% on the reduction peak current is observed (highlighted by a circle). Subsequently, the peak currents slowly increase with stepwise addition of Fe(III) up

Fig. 3. (a) Dependence of stripping current of 20 ␮g L−1 As(III) on the concentration of HA with/without Fe(III). (b) Dependence of stripping current of 20 ␮g L−1 As(III) on the concentration of Fe(III) with/without HA.

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to 40 mg L−1 , that is, the peak currents are gradually recovered to their initial values. In the presence of 20 mg L−1 HA, the current has returned to 99.2% of initial value when adding 20 mg L−1 Fe(III). Further adding 40 mg L−1 Fe(III), the current almost completely recovered. Similarly, when 0.5 M H2 SO4 contains 40 mg L−1 HA, 96.9% and 98.1% of initial value are obtained with adding 20 mg L−1 and 40 mg L−1 Fe(III), respectively. These experiments confirm that the binding affinity between Fe(III) and HA molecules is stronger than that between HA with Au microwire electrode. The former could efficiently prevent the decrease on the peak currents which is due to the addition of HA.

3.3. Stripping response of As(III) when HA and Fe(III) co-existing The electrochemical response of As(III) under co-existing HA and Fe(III) was concerned and the results are illustrated in Fig. 3. The data were collected from the voltammetric responses of 20 ␮g L−1 As(III) in N2 H4 ·2HCl solution (pH 0.5) by using SWASV. Fig. 3a shows the stripping current of As(III) in the presence of HA by adding Fe(III) (0, 20, 40 mg L−1 ). It can be observed that the responses of As(III) gradually decrease along with the addition of HA up to 40 mg L−1 . When no Fe(III) exists in N2 H4 ·2HCl solution, the responses of As(III) decrease by 21.3% and 30.0% in the presence of 20 mg L−1 and 40 mg L−1 HA, respectively. However, when adding 20 mg L−1 Fe(III), only 8.5% and 17.2% in decrease are observed in the presence of 20 mg L−1 and 40 mg L−1 HA, respectively. And a decrease of 3.2% and 6.5% in responses can be found in solution containing 40 mg L−1 Fe(III) in the presence of 20 mg L−1 and 40 mg L−1 HA. The more Fe(III) contains in solution, the smaller of the interference of HA on the responses toward As(III) is. Alternatively, a test of HA addition (0, 20, 40 mg L−1 ) to As(III) in the presence of Fe(III) was performed, as shown in Fig. 3b. In the case of HA-free solution, the responses of As(III) are almost stable with continuous addition of Fe(III) and the RSD is 2.5%. While in the case of the solution containing 20 or 40 mg L−1 HA, 18.0% or 22.9% in the response of As(III) is decreased (highlighted by a circle). Interestingly, along with the continuous addition of Fe(III), the recovery of the responses can be apparently observed. In the presence of 20 mg L−1 HA, the response is recovered from 81.8% of the initial value to its 98.7% with adding Fe(III) from 0 to 40 mg L−1 . Similarly, with regard to the solution containing 40 mg L−1 HA, 81.1% of the initial response is recovered to its 96.7% with adding Fe(III) from 0 to 40 mg L−1 . On the basis of the analysis, we suggest that the loss of As(III) signal in the presence of HA is most likely due to gold surface blockage by HA adsorption and possibly, also by a weak complexation of As(III) with HA [36]. The synergetic interactions lead to the decrease in voltammetric responses of As(III). Furthermore, it is much interesting that Fe(III) in this system is thought to be of great benefit for eliminating the interference of HA, thus facilitating electrochemical measurement of As(III). The analytical performance toward As(III) was typically compared, as shown in Supporting information, Fig. S4. As seen, the sensitivity decreased in the presence of HA molecules. Interestingly, after adding Fe(III), the sensitivity is the same as that in the absence of HA. Note that the calibration curves (Fig. S4) obtained in the range 10–100 ppb of As(III) are not going through the origin. This is reflecting the usually short linear range that is obtained for the detection of arsenic on gold [38–40]. With comprehensively considering the above discussion, it can be concluded that co-existed Fe(III) in groundwater can efficiently eliminate the influence of HA on the As(III) detection, which may be attributed to the possibly strong interaction between Fe(III) and HA molecules. To further illustrate the potential interaction of HA with Fe(III) and As(III), we next seek to find evidence of their binding using FTIR and XPS.

Fig. 4. (a) FTIR spectra of HA with addition of different amounts of As(III) (0, 5, 10, 15, 20, 25 ␮g L−1 ). (b) Enlarged FTIR spectra extracted from the marked area in panel a.

3.4. FTIR analysis of HA–As(III) and HA–Fe(III) Fig. 4 shows FTIR spectra of HA with addition of different amounts of As(III) (0, 5, 10, 15, 20, 25 ␮g L−1 ). These samples were prepared in 0.038 M N2 H4 ·2HCl solution (pH 0.5). It can be seen that pure HA shows a typical peak at 3408.2 cm−1 , which can be assigned to the asymmetric stretching vibration of carboxylic group ( COOH) and C H, N H stretching. Two small bands around 2926.6 and 2854.9 cm−1 (Fig. 4a) correspond to aliphatic stretching vibrations [41,42]. Enlarged FTIR spectra extracted from the marked area in panel a are shown in Fig. 4b. The broad band near 1640.6 cm−1 is attributed to aromatic C C, asymmetric C O stretching in carboxylic groups and bending of NH2 . The stretches of C C and bending of NH are located at 1532.5 cm−1 [43]. Peak at 1399.7 cm−1 may be contributed to the stretching of carboxylate. Peaks at 1203.5 and 1075.9 cm−1 are assigned to bending vibration of the aromatic rings and OH stretching of phenolic-OH [44]. The FTIR spectra of HA–As(III) are much similar to that of pure HA. Only that the shoulder peak associating with OH stretching at 1093.3 cm−1 is more apparent with increasing the amount of As(III) [45]. It is known that the pKa values of As(OH)3 are 9.2, 12.13 and 13.4, indicating that As(III) is maintained predominantly in As(OH)3 at low pH (0.5) [24]. The shoulder peak at 1093.3 cm−1 can be attributed to the weakening interaction or deprotonation in

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Fig. 5. FTIR spectra of HA with addition of different amounts of Fe(III) (0, 10, 20, 30, 40 mg L−1 ).

hydroxy of phenolic-OH as the increasing hydrogen-bond interaction between oxygen in phenolic-OH and OH–As [46]. These results indicate that the influence of HA on As(III) is derived from the interaction based on hydrogen bonding. In addition, a “coiled” structure of HA at low pH [47] can also cause a slight physical interaction with As(III). These interactions may decrease the activity of As(III) in solution and are responsible for the decrease in SWASV response of As(III). Fig. 5 shows the FTIR spectra of HA–Fe(III) complexes as well as pure HA ranging from 1800 to 700 cm−1 . In comparison with pure HA, some obvious peaks appear at 1724.3, 1488.2, 1406.1, 1207.4 and 1093.6 cm−1 . Their intensities become stronger with increasing the amount of Fe(III). The shoulder peak at 1724.3 cm−1 becomes clear, which is probably related to C O stretch in carbonyl [41]. New peaks appearing in Fe(III)–HA complex at 1488.2 and 1406.1 cm−1 are contributed to the asymmetric stretching of CH3 and COO− based on the effect of Fe(III) [48]. The presence of Fe(III)–HA complex may be evidenced by the peaks at 1207.4 and 1093.6 cm−1 , which results from hydrogen deformation and nitrogen containing ring structure [41]. It is worthwhile mentioning that HA acts as a ligand to support several reactive donor sites. Based on the formation of Fe(III)–HA complex, Fe(III) can efficiently eliminate the effect of HA on the voltammetric responses of As(III), thus facilitating the electrochemical measurements. 3.5. XPS analysis of HA–As(III) and HA–Fe(III) X-ray photoelectron spectroscopy (XPS) was further used to investigate the interaction between HA and As(III) or Fe(III). Fig. 6 shows the high-resolution XPS spectra of O 1s and N 1s. For the oxygen element (Fig. 6a), the band at the lower binding energy of 532.17 eV is assigned to oxygen in C O. The band at 532.92 eV can be related to C O in carboxylic, epoxy, or phenol groups of HA molecules [49,50]. For the nitrogen element (Fig. 6b), the NI at 400.01 eV is assigned to the N atoms in pyridinic and pyrazine rings, whereas the NII band of 401.19 eV can be attributed to the N atoms in aromatic rings [49]. Compared with the XPS spectra of HA, no obvious change on the bands with O 1s and N 1s in HA–As(III) can be observed, indicating the weak interaction between HA and As(III). However, the peaks of 530.88 eV for O 1s and 399.07 eV for N 1s can be deconvoluted in HA–Fe(III) complex, which can be assigned to Fe O and Fe N bands [49,51]. The similar results can also be found in the complex including HA, As(III) and Fe(III). It

Fig. 6. XPS spectra of (a) O 1s and (b) N 1s for the HA, HA–As(III), HA–Fe(III), and HA–As(III)–Fe(III).

demonstrates that HA molecules can complex with Fe(III) in these acidic conditions and the interaction between them is stronger than that of HA–As(III). Fig. 7 shows the As 3d and Fe 2p regions for the four substances. As seen from Fig. 7a, the peak of As can be observed in HA–As(III), indicating the interaction between HA and As(III). A minority of As(V) deconvoluted at 44.88 eV is attributed to oxidation of As(III) during experiment process. As predicted, no signal for As(III) could be seen when Fe(III) is coexisted with HA and As. In addition, the atom ratio of As to C (As/C) decreases from 3.2% (in HA–As) to be less than 0.1% (in HA–As–Fe complex). These results from the weak interaction between HA molecules and As(III). However, compared with the XPS spectra of HA–Fe(III), the bands for Fe 2p can be still observed in HA–As–Fe complex (Fig. 7b). This indicates that HA molecules can be prior to complexing with Fe(III) when As(III) and Fe(III) compete for the same surface adsorption sites of HA molecules [52]. Besides, the XPS spectra for Fe 2p bands in HA–Fe and HA–As–Fe complexes are corresponding to Fe 2p1/2 (724.81 ± 0.01 eV) and Fe 2p3/2 (711.03 ± 0.01 eV) asymmetric bands derived from the spin–orbital splitting, revealing that ferric state is dominant in these complexes [49]. Overall, the XPS results are in good accordance with the obtained electrochemical results and FTIR analysis, which confirms the importance of Fe(III) in eliminating the interference of HA on the electrochemical analysis of

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4. Conclusions We have electrochemically demonstrated that the stripping current of As(III) will decrease when increasing the concentration of HA due to electrode surface blockage by HA adsorption and a possible weak complexation between HA and As(III). Such a decrease could be eliminated by the addition of Fe(III). It is suggested that HA could easily interact with Fe(III) in contrast to As(III) or Au electrode. FTIR and XPS provide detailed information about the interaction between HA and Fe(III) or As(III). However, considering the complexity of component in real environmental water, maybe more works should be done by choosing more metal and organic compounds. This work simplifies the experimental set-up and provides an example of alternative interference study. We believe that it offers an deep understanding on the interference during electrochemical determination of As(III) as compared to the present state-of-the-art researches. Acknowledgments This work was supported by the National Basic Research Program of China (2011CB933700) and National Natural Science Foundation of China (61102013 and 21377131). X.-J.H. acknowledges the CAS Institute of Physical Science, University of Science and Technology of China (2012FXCX008), for financial support. 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.jhazmat. 2013.12.054. References

Fig. 7. XPS spectra of (a) As 3d and (b) Fe 2p for the HA, HA–As(III), HA–Fe(III), and HA–As(III)–Fe(III).

As(III). Based on the above electrochemical experiments and FTIR and XPS results, a schematic illustration of how existence of Fe(III) affects the interference of humic acid on electrochemical response toward As(III) is depicted in Fig. 8.

Fig. 8. A schematic illustration of how existence of Fe(III) affects the interference of humic acid on electrochemical response toward As(III).

[1] A. Mukherjee, P. Bhattacharya, F. Shi, A.E. Fryar, A.B. Mukherjee, Z.M. Xie, G. Jacks, J. Bundschuh, Chemical evolution in the high arsenic groundwater of the Huhhot basin (Inner Mongolia, PR China) and its difference from the western Bengal basin (India), Appl. Geochem. 24 (2009) 1835–1851. [2] A. Smith, P. Lopipero, J. Chung, R. Haque, A. Hernandez, L. Moore, C. Steinmaus, Arsenic in drinking water and cancer risks estimated from epidemiological studies in Argentina, Chile, Taiwan and Japan, Epidemiology 11 (2000) S93. [3] R.K. Kwok, P. Mendola, Z.Y. Liu, D.A. Savitz, G. Heiss, H.L. Ling, Y. Xia, D. Lobdell, D. Zeng, J.M. Thorp, J.P. Creason, J.L. Mumford, Drinking water arsenic exposure and blood pressure in healthy women of reproductive age in Inner Mongolia, China, Toxicol. Appl. Pharmacol. 222 (2007) 337–343. [4] Z. Ning, D.T. Lobdell, R.K. Kwok, Z. Liu, S. Zhang, C. Ma, M. Riediker, J.L. Mumford, Residential exposure to drinking water arsenic in Inner Mongolia, China, Toxicol. Appl. Pharmacol. 222 (2007) 351–356. [5] C. B’Hymer, J.A. Caruso, Arsenic and its speciation analysis using highperformance liquid chromatography and inductively coupled plasma mass spectrometry, J. Chromatogr. A 1045 (2004) 1–13. [6] H.R. Hansen, A. Raab, J. Feldmann, New arsenosugar metabolite determined in urine by parallel use of HPLC–ICP-MS and HPLC–ESI-MS, J. Anal. At. Spectrom. 18 (2003) 474–479. [7] Y. Arai, A. Lanzirotti, S. Sutton, J.A. Davis, D.L. Sparks, Arsenic speciation and reactivity in poultry litter, Environ. Sci. Technol. 37 (2003) 4083–4090. [8] Y. Wei, L.T. Kong, R. Yang, L. Wang, J.H. Liu, X.J. Huang, Electrochemical impedance determination of polychlorinated biphenyl using a pyrenecyclodextrin-decorated single-walled carbon nanotube hybrid, Chem. Commun. 47 (2011) 5340–5342. [9] Y. Wei, C. Gao, F.L. Meng, H.H. Li, L. Wang, J.H. Liu, X.J. Huang, SnO2 /reduced graphene oxide nanocomposite for the simultaneous electrochemical detection of cadmium(II), lead(II), copper(II), and mercury(II): an interesting favorable mutual interference, J. Phys. Chem. C 116 (2012) 1034–1041. [10] Y. Wei, R. Yang, Y.X. Zhang, L. Wang, J.H. Liu, X.J. Huang, High adsorptive gammaAlOOH(boehmite)@SiO2 /Fe3 O4 porous magnetic microspheres for detection of toxic metal ions in drinking water, Chem. Commun. 47 (2011) 11062–11064. [11] X. Dai, O. Nekrassova, M.E. Hyde, R.G. Compton, Anodic stripping voltammetry of arsenic(III) using gold nanoparticle-modified electrodes, Anal. Chem. 76 (2004) 5924–5929. [12] L. Xiao, G.G. Wildgoose, R.G. Compton, Sensitive electrochemical detection of arsenic (III) using gold nanoparticle modified carbon nanotubes via anodic stripping voltammetry, Anal. Chim. Acta 620 (2008) 44–49. [13] A.O. Simm, C.E. Banks, R.G. Compton, Sonically assisted electroanalytical detection of ultratrace arsenic, Anal. Chem. 76 (2004) 5051–5055.

160

Z.-G. Liu et al. / Journal of Hazardous Materials 267 (2014) 153–160

[14] B.K. Jena, C.R. Raj, Gold nanoelectrode ensembles for the simultaneous electrochemical detection of ultratrace arsenic, mercury, and copper, Anal. Chem. 80 (2008) 4836–4844. [15] M.R. Rahman, T. Okajima, T. Ohsaka, Selective detection of As(III) at the Au(111)-like polycrystalline gold electrode, Anal. Chem. 82 (2010) 9169–9176. [16] E. Majid, S. Hrapovic, Y.L. Liu, K.B. Male, J.H.T. Luong, Electrochemical determination of arsenite using a gold nanoparticle modified glassy carbon electrode and flow analysis, Anal. Chem. 78 (2006) 762–769. [17] S. Hrapovic, Y.L. Liu, J.H.T. Luong, Reusable platinum nanoparticle modified boron doped diamond microelectrodes for oxidative determination of arsenite, Anal. Chem. 79 (2007) 500–507. [18] K.B. Male, S. Hrapovic, J.M. Santini, J.H.T. Luong, Biosensor for arsenite using arsenite oxidase and multiwalled carbon nanotube modified electrodes, Anal. Chem. 79 (2007) 7831–7837. [19] Y. Song, G.M. Swain, Development of a method for total inorganic arsenic analysis using anodic stripping voltammetry and a Au-coated, diamond thin-film electrode, Anal. Chem. 79 (2007) 2412–2420. [20] R. Feeney, S.P. Kounaves, On-site analysis of arsenic in groundwater using a microfabricated gold ultramicroelectrode array, Anal. Chem. 72 (2000) 2222–2228. [21] J.M. Zen, P.Y. Chen, A.S. Kumar, Flow injection analysis of an ultratrace amount of arsenite using a Prussian blue-modified screen-printed electrode, Anal. Chem. 75 (2003) 6017–6022. [22] T.A. Ivandini, R. Sato, Y. Makide, A. Fujishima, Y. Einaga, Electrochemical detection of arsenic(III) using iridium-implanted boron-doped diamond electrodes, Anal. Chem. 78 (2006) 6291–6298. [23] C. Gao, X.Y. Yu, S.Q. Xiong, J.H. Liu, X.J. Huang, Electrochemical detection of arsenic(III) completely free from noble metal: Fe3 O4 microspheres-room temperature ionic liquid composite showing better performance than gold, Anal. Chem. 85 (2013) 2673–2680. [24] P. Salaun, B. Planer-Friedrich, C.M.G. van den Berg, Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode, Anal. Chim. Acta 585 (2007) 312–322. [25] J. Zima, C.M.G. Van Den Berg, Determination of arsenic in sea-water by cathodic stripping voltammetry in the presence of pyrrolidine dithiocarbamate, Anal. Chim. Acta 289 (1994) 291–298. [26] K. Gibbon-Walsh, P. Salaun, C.M.G. van den Berg, Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode, Anal. Chim. Acta 710 (2012) 50–57. [27] P. Salaun, K.B. Gibbon-Walsh, G.M.S. Alves, H.M.V.M. Soares, C.M.G. van den Berg, Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode, Anal. Chim. Acta 746 (2012) 53–62. [28] G.M.S. Alves, J.M.C.S. Magalhaes, P. Salaun, C.M.G. van den Berg, H.M.V.M. Soares, Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode, Anal. Chim. Acta 703 (2011) 1–7. [29] K. Gibbon-Walsh, P. Salaun, C.M.G. van den Berg, Arsenic speciation in natural waters by cathodic stripping voltammetry, Anal. Chim. Acta 662 (2010) 1–8. [30] K. Gibbon-Walsh, P. Salaun, M.K. Uroic, J. Feldmann, J.M. McArthur, C.M.G. van den Berg, Voltammetric determination of arsenic in high iron and manganese groundwaters, Talanta 85 (2011) 1404–1411. [31] H. Li, R.B. Smart, Determination of sub-nanomolar concentration of arsenic(III) in natural waters by square wave cathodic stripping voltammetry, Anal. Chim. Acta 325 (1996) 25–32. [32] Y. Song, G.M. Swain, Total inorganic arsenic detection in real water samples using anodic stripping voltammetry and a gold-coated diamond thin-film electrode, Anal. Chim. Acta 593 (2007) 7–12. [33] Y.C. Sun, J. Mierzwa, M.H. Yang, New method of gold-film electrode preparation for anodic stripping voltammetric determination of arsenic (III and V) in seawater, Talanta 44 (1997) 1379–1387.

[34] S. Sounderajan, G.K. Kumar, S.A. Kumar, A.C. Udas, G. Venkateswaran, Characterization of As(V), As(III) by selective reduction/adsorption on palladium nanoparticles in environmental water samples, Talanta 78 (2009) 1122–1128. [35] J. Lastincova, L. Jurica, E. Beinrohr, Determination of arsenic in soil extracts by flow-through anodic stripping coulometry, Pol. J. Environ. Stud. 13 (2004) 533–536. [36] P. Warwick, E. Inam, N. Evans, Arsenic’s interaction with humic acid, Environ. Chem. 2 (2005) 119–124. [37] T. Wang, F.P. Zhong, Y.H. Yang, D.H. Zhang, Fourier transform surface-enhanced Raman spectra of fulvic and humic acids adsorbed on Au electrodes, Spectrosc. Lett. 29 (1996) 1449–1458. [38] A. Giacomino, O. Abollino, M. Lazzara, M. Malandrino, E. Mentasti, Determination of As(III) by anodic stripping voltammetry using a lateral gold electrode: experimental conditions, electron transfer and monitoring of electrode surface, Talanta 83 (2011) 1428–1435. [39] M. Khairy, D.K. Kampouris, R.O. Kadara, C.E. Banks, Gold nanoparticle modified screen printed electrodes for the trace sensing of arsenic(III) in the presence of copper(II), Electroanalysis 22 (2010) 2496–2501. [40] M.F. Wang, Q.A. Huang, X.Z. Li, Y. Wei, Mesoporous CuO: alternative enzymefree glucose sensing structure with excellent kinetics of electrode process, Anal. Methods 4 (2012) 3174–3179. [41] J.J. Alberts, Z. Filip, Metal binding in estuarine humic and fulvic acids: FTIR analysis of humic acid–metal complexes, Environ. Technol. 19 (1998) 923–931. [42] X.X. Ou, S. Chen, X. Quan, H.M. Zhao, Photochemical activity and characterization of the complex of humic acids with iron(III), J. Geochem. Explor. 102 (2009) 49–55. [43] L.T. Kong, J. Wang, Y. Jia, Z. Guo, J.H. Liu, FT-IR and FT-Raman investigations of the chemosensing material para-hexafluoroisopropanol aniline, J. Raman Spectrosc. 41 (2010) 989–995. [44] H.B. Fu, X. Quan, Complexes of fulvic acid on the surface of hematite, goethite, and akaganeite: FTIR observation, Chemosphere 63 (2006) 403–410. [45] F.N. Crespilho, V. Zucolotto, J.R. Siqueira Jr., C.J. Constantino, F.C. Nart, O.N. Oliveira Jr., Immobilization of humic acid in nanostructured layer-by-layer films for sensing applications, Environ. Sci. Technol. 39 (2005) 5385–5389. [46] J. Buschmann, A. Kappeler, U. Lindauer, D. Kistler, M. Berg, L. Sigg, Arsenite and arsenate binding to dissolved humic acids: influence of pH, type of humic acid, and aluminum, Environ. Sci. Technol. 40 (2006) 6015–6020. [47] S.B. Yang, J. Hu, C.L. Chen, D.D. Shao, X.K. Wang, Mutual effects of Pb(II) and humic acid adsorption on multiwalled carbon nanotubes/polyacrylamide composites from aqueous solutions, Environ. Sci. Technol. 45 (2011) 3621–3627. [48] X.Q. Lu, A.M. Vassallo, W.D. Johnson, Thermal stability of humic substances and their metal forms: an investigation using FTIR emission spectroscopy, J. Anal. Appl. Pyrol. 43 (1997) 103–113. [49] A. Velazquez-Palenzuela, L. Zhang, L.C. Wang, P.L. Cabot, E. Brillas, K. Tsay, J.J. Zhang, Carbon-supported Fe–Nx catalysts synthesized by pyrolysis of the Fe(II)-2,3,5,6-tetra(2-pyridyl)pyrazine complex: structure, electrochemical properties, and oxygen reduction reaction activity, J. Phys. Chem. C 115 (2011) 12929–12940. [50] J.H. Liu, X.Y. Yu, T. Luo, Y.X. Zhang, Y. Jia, B.J. Zhu, X.C. Fu, X.J. Huang, Adsorption of lead(II) on O2 -plasma-oxidized multiwalled carbon nanotubes: Thermodynamics, kinetics, and desorption, ACS Appl. Mater. Interfaces 3 (2011) 2585–2593. [51] L. Armelao, R. Bertoncello, L. Crociani, G. Depaoli, G. Granozzi, E. Tondello, M. Bettinelli, XPS and UV–vis study of high-purity Fe2 O3 thin-films obtained using the sol–gel technique, J. Mater. Chem. 5 (1995) 79–83. [52] I. Ko, J.Y. Kim, K.W. Kim, Arsenic speciation and sorption kinetics in the Ashematite-humic acid system, Colloids Surf. A: Physicochem. Eng. Asp. 234 (2004) 43–50.