Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite

Materials Science and Engineering C 33 (2013) 1514–1520

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Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec

Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite Meixia Zheng a, Feng Gao a, Qingxiang Wang a,⁎, Xili Cai a, Shulian Jiang b, Lizhang Huang b, Fei Gao a a b

Department of Chemistry and Environmental Science, Zhangzhou Normal University, Zhangzhou 363000, China Zhangzhou Product Quality Supervision and Inspection Institute, Zhangzhou 363000, China

a r t i c l e

i n f o

Article history: Received 1 June 2012 Received in revised form 27 November 2012 Accepted 17 December 2012 Available online 23 December 2012 Keywords: Graphene–chitosan composite Acetaminophen Electrochemistry Determination

a b s t r a c t The electrochemical behaviors of acetaminophen (ACOP) on a graphene–chitosan (GR–CS) nanocomposite modified glassy carbon electrode (GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Electrochemical characterization showed that the GR–CS nanocomposite had excellent electrocatalytic activity and surface area effect. As compared with bare GCE, the redox signal of ACOP on GR–CS/GCE was greatly enhanced. The values of electron transfer rate constant (ks), diffusion coefficient (D) and the surface adsorption amount (Γ⁎) of ACOP on GR–CS/GCE were determined to be 0.25 s−1, 3.61×10−5 cm2 s−1 and 1.09×10−9 mol cm−2, respectively. Additionally, a 2e−/2H+ electrochemical reaction mechanism of ACOP was deduced based on the acidity experiment. Under the optimized conditions, the ACOP could be quantified in the range from 1.0×10−6 to 1.0×10−4 M with a low detection limit of 3.0×10−7 M based on 3S/N. The interference and recovery experiments further showed that the proposed method is acceptable for the determination of ACOP in real pharmaceutical preparations. © 2012 Elsevier B.V. All rights reserved.

1. Introduction As an acetyl aniline drug, acetaminophen (ACOP) has antipyretic and analgesic functions, which is suitable for the remedy of fever, headache, joint ache, rheumatism pain and various neuralgia, migraine and dysmenorrhea [1]. However, the overdoses of ACOP are harmful to the human body including the digestive, urinary, blood and respiratory systems [2,3]. Therefore, it is very valuable to establish new methods to accurately monitor and detect the content of this drug. Up to now, many methods have been developed for the analysis of ACOP, which includes spectrophotometry [4], titrimetry [5], fluorescence spectroscopy [6], chromatography [7] and electrochemical methods [8–11]. Compared with the other technologies, the electrochemical method shows the advantages of simplicity, low cost and high sensitivity [8–11]. However, the poor electrochemical response of ACOP on the common electrodes often limits its application in practical analysis. In order to overcome this disadvantage, the chemically modified electrodes are often designed and applied. For example, Boopathi et al. [8] have reported the electrocatalysis of ACOP on a conducting copper ion-containing terthiophene carboxylic acid polymer (Cu-poly-TTCA) modified electrode. The results showed that the electrochemical response of ACOP on the modified electrode was greatly promoted due to Cu(II) species. The similar promotions of ACOP electrochemistry were also observed on the electrode modified with nano-sized materials like polyaniline-multi-walled carbon ⁎ Corresponding author. Tel.: +86 596 2591445; fax: +86 596 2520035. E-mail address: [email protected] (Q. Wang). 0928-4931/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2012.12.055

nanotubes (PANI-MWCNTs) composite [9], Pd nanoparticles incorporated poly(3-methylthiophene) composite [10], Co(OH)2 [11], etc. Graphene (GR), a one-atom-thick sp2-bonded carbon sheet has attracted extensive attention of scientific and technological researchers since it was first discovered in 2004 by Novoselov and Geim [12]. Due to its high surface area, excellent conductivity and mechanical strength, the material displays its promising potential for application in the fields of microelectrical device, filed-effect transistor and ultrasensitive sensor [13,14]. The application of graphene as a novel electrochemical sensing material attracts considerable attention, and it has been reported that many biological molecules such as dopamine [15], cytochrome c [16], glucose oxidase [17] and DNA [18], and the inorganic metal ions of Pb2+ [19] and Cd 2+ [20] all showed enhanced electrochemical response on the graphene modified electrodes. Chitosan (CS) is one of the most widely used biopolymers for sensor applications due to its nontoxic nature, excellent film-forming ability, good mechanical strength, high permeability and cost-effectiveness characteristics [21,22]. However, in its normal state, CS film has very low electrical conductivity and high degree of swelling, which often results in a low sensitivity for the determination of the analytes [21,23]. In order to circumvent these problems, doping with some conductive nanoparticles like carbon nanotubes [24,25], gold nanoparticles [26] and SiO2 [27] is often adopted, by which the analytical performance of the modified electrodes can be dramatically improved because of the synergistic effect from the chitosan and the nanoparticles. In this work, a nanocomposite of graphene–chitosan (GR–CS) was fabricated and applied to modify glassy carbon electrode (GCE). The obtained modified electrode (GR–CS/GCE) was electrochemically

M. Zheng et al. / Materials Science and Engineering C 33 (2013) 1514–1520

characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)6] 3−/4− as redox probe. The results showed that the modified electrode showed excellent conductivity and surface area effect, and meanwhile the modified film of GR–CS on GCE revealed good stability due to the remarkable film-forming property of CS. The electrochemical behaviors of ACOP were carefully studied on GR–CS/GCE, which showed that GR–CS/GCE exhibited excellent electrocatalytic activity toward the redox of ACOP. Under the optimized conditions, the sensor shows high sensitivity, good selectivity and low detection limit for the determination of ACOP.

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A

2. Experimental 2.1. Chemicals and reagents ACOP was purchased from Sinopharm Chemical Reagent Co., Ltd (China); Chitosan was provided by Sanland Chemical Co., Ltd (USA); The graphene sheets were prepared in our lab according to the modified Hummer's method [28]; N, N-dimethylformamide (DMF) was purchased from Xilong Chemical Co., Ltd (China); Britton–Robinson (B–R) buffer solutions of required pH were prepared by adding 0.4 M acetic acid and 0.4 M boric acid into a solution of 0.4 M phosphoric acid. The pH was adjusted with the appropriate amount of 0.2 M NaOH. All the other chemicals were of analytical reagent grades and were purchased commercially. Doubly distilled water (DDW) was used throughout this experiment.

B

2.2. Apparatus The scanning electron microscopic (SEM) morphologies of the chemically reduced GR nanosheets and its composite with chitosan (GR–CS) were recorded on a LEO 1530 scanning electron microscope (Germany). A CHI 650 C electrochemical analyzer (Shanghai CH Instrument, China) was used for all the electrochemical measurements. A conventional three-electrode system consisted of a bare or GR–CS modified GCE (GR–CS/GCE) as working electrode, a platinum wire as auxiliary electrode and an Ag/AgCl/3 M KCl as reference electrode. The nominal surface area of the bare GCE was calculated to be 0.031 cm 2 according to the disk diameter of 2 mm. All the peak current densities were determined based on the nominal surface area of the bare GCE.

C

2.3. Preparation of the GR–CS/GCE Prior to use, the bare GCE was polished to a mirror-like surface with 0.05 μm, 0.3 μm and 0.5 μm α-Al2O3, respectively, and rinsed ultrasonically with DDW, absolute ethanol and DDW, in turn. A chitosan solution (0.3%) was prepared by dissolving about 0.003 g of chitosan in 1 mL acetic acid, and then 1 mg GR dissolved in 1 mL DMF was added and ultrasonically dispersed for 1 h to obtain a well-dispersed black suspension. Then 10 μL of the prepared GR–CS solution was cast on the pretreated GCE and allowed to dry at room temperature. Before use, the modified electrode was carefully rinsed with DDW to remove the loosely attached GR–CS, and thus a GR–CS/GCE was obtained. For comparison, the CS modified GCE (CS/GCE) or GR modified GCE (GR/GCE) was also prepared by the same way except replacing the GR–CS nanocomposite solution with the single-component CS or GR solution. 3. Results and discussion 3.1. Morphological and electrochemical characterization of GR–CS Fig. 1A shows the SEM images of pristine graphene nanosheets and their composite with chitosan, GR–CS. For the pristine graphene, a typical wrinkle and thin-flake structure can be clearly observed

Fig. 1. (A) SEM images of pristine GR (inset) and GR–CS nanocomposite (main panel). CV (B) and EIS (C) images of 5.0 mM [Fe(CN)6]3−/4− with 0.1 M KCl at bare GCE (a), CS/GCE (b) and GR–CS/GCE (c).

(inset), suggesting the successful preparation of GR nanosheets in this work. When the GR material was dispersed in the CS gel solution by ultrasonication, a stable and dark suspension was formed, and the SEM image shows that nanocomposite film (main panel) becomes more uniform and flat in comparison with pristine graphene nanosheets due to the good film-forming property of CS. Additionally, the specific wrinkle structure of GR can also be seen on the local position of the GR–CS film (see the arrow), indicating that the GR nanosheets are not aggregated in the nanocomposite and the high surface area of GR is maintained. The electrochemistry of GR–CS was characterized by CV in a mixture of 5.0 mM [Fe(CN)6] 3−/4− and 0.1 M KCl. As shown in Fig. 1B, a pair of well-defined redox peaks is observed on the bare GCE with the peak-to-peak separation (ΔEp) of 0.10 V. The oxidative peak current density (jpa) and the reduction peak current density (jpc) were determined to be − 1.90 mA cm −2 and 1.87 mA cm −2 (curve a), respectively. When the same solution was detected with CS/GCE, jpa and jpc were decreased to − 1.64 mA cm −2 and 1.45 mA cm −2 (curve

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M. Zheng et al. / Materials Science and Engineering C 33 (2013) 1514–1520

 1=2 1=2 3 3=2 1=2 Ipa ¼ 0:4463 F =RT n A0 D0 C 0 v

I/µA

b), respectively, and meanwhile the ΔEp increased to 0.16 V. These results suggest that the electrochemical response of the electroactive probe is weakened by the CS film because of the inferior conductivity of CS [23]. However, on GR–CS/GCE, the jpa and jpc are sharply increased to −46.8 mA cm −2 and 44.5 mA cm −2 (curve c), respectively, suggesting that the electrochemical activity of [Fe(CN)6] 3−/4− is significantly enhanced by GR in the GR–CS composite film. Additionally, the background currents (current carrying capacities) are also increased obviously on the GR–CS/GCE, indicating that the specific surface area is also enlarged by the GR–CS film [29]. To testify this conclusion, the effective surface areas (A0) of the different electrodes were quantitatively calculated according to the following Randles– Sevcik formula [30]:

I/10-4A

E/V(vs.Ag/AgCl/3 M KCl)

a b

E/V(vs.Ag/AgCl/3 M KCl)

ð1Þ

where Ipa is the oxidation peak current, n the electron transfer number, F the Faraday, R the universal gas constant, v the scan rate, T the Kelvin temperature, A0 the effective electrode area, v the scan rate, C0 and D0 the molar concentration and diffusion coefficient of [Fe(CN)6] 4−, respectively. Therefore under the measured conditions (T = 298 K, v = 0.1 V s −1, C0 = 5.0 mM, D0 = 7.6 × 10 −6 cm 2 s −1) in this work, the A0 values of bare GCE, CS/GCE and GR–CS/GCE were determined to be 0.044 cm 2, 0.050 cm 2 and 0.124 cm 2, respectively, further confirming the high surface effect of GR–CS composite film on the electrochemical response of the electroactive molecules. In addition to the high specific surface area, the superior electronic conductivity is also a notable feature for the GR material [31]. In this work, the contribution of GR to the electron conductivity of the modified electrode was further investigated by a sensitive electrochemical impedance method. It is well known that the Nyquist diagram obtained by electrochemical impedance method often consisted of a semicircle part at the high frequency region and a straight line part at the low frequency region. The diameter of the semicircle part reflects the electron-transfer resistance (Ret), which controls the electron transfer kinetics of the redox probe at the electrode interface [32]. In this work, the typical Nyquist plots of 5.0 mM [Fe(CN)6] 3−/4− solution containing 0.1 M KCl at bare GCE (curve a), CS/GCE (curve b) and GR–CS/GCE (curve c) are shown in Fig. 1C and the corresponding Ret value on each electrode is displayed as a histogram in the inset. It can be clearly seen that the semicircle is small on bare GCE (Ret =335 Ω), but on CS/GCE, the semicircle diameter is significantly increased to about 900 Ω, further suggesting that the electron-transfer process of the electroactive [Fe(CN)6]3−/4− molecules is blocked due to the inferior conductivity of CS film. However, on GR–CS/GCE, the semicircle at the high frequency region is dramatically decreased, which indicates that the electron transfer resistance of [Fe(CN)6] 3−/4− on GR–CS/GCE is greatly decreased as compared with that on chitosan modified GCE or even the bare GCE surface. This also proves that the material of GR used in this work greatly enhances the conductivity of the interface [9,31]. Summarily, the above results exhibit that the prepared GR–CS/GCE shows significant surface area effect and electron-transfer promoting action as a new generation of the electroanalysis sensing platform. It is also needed to note that the single-component GR solution (without CS) was also applied to prepare GR modified GCE (GR/GCE). However, it is showed that although the electrochemical signal of [Fe(CN)6] 3−/4− is larger than that on the CS/GCE, the GR materials are very easy to coagulate in DMF medium, and the GR particles can be easily peeled off from the modified electrode during measurements, making the single-component of GR not suitable as the sensing material. 3.2. Electrochemical properties of ACOP at GR–CS/GCE Fig. 2 shows the electrochemical response of pH 7.0 B–R buffer solution with and without ACOP on different electrodes. It is observed

Fig. 2. CVs of 40 mM B–R (pH 7.0) in the absence (a) and presence of (b) 1.0 × 10−4 M ACOP on the GR–CS/GCE. Inset is the CV of 1.0 × 10−4 M ACOP in 40 mM B–R (pH 7.0) at the bare GCE. Scan rate: 0.1 V s−1.

that there is no redox peak in CVs for the blank B–R buffer on bare GCE (date not shown) and GR–CS/GCE (curve a). When 1.0× 10−4 M ACOP was added into the buffer solution, a pair of redox peaks appeared on bare GCE with the jpa and jpc of − 0.048 mA cm − 2 and 0.026 mA cm − 2, respectively (inset of Fig. 2). Alternatively, when GR–CS/GCE was applied for measurement, it is found that the jpa and jpc values of ACOP are remarkably increased to − 1.0 mA cm − 2 and 0.81 mA cm − 2 (curve b), respectively, suggesting that the modification of the film significantly promotes the electrochemical responses of ACOP. In addition, compared with bare GCE, the ratio of the oxidation peak current to the reduction peak current is changed from 1.8 to 1.2, and the ΔEp is decreased from 245 mV to 190 mV, suggesting that the electron transfer reversibility of ACOP is also changed better by using the sensing material of GR–CS. Furthermore, according to the Faraday's equation [18]: 

Γ ¼ Q =nFA0

ð2Þ

where Γ⁎ is the surface adsorption amount, Q the charge, and the Γ⁎ value of ACOP on the GR–CS/GCE was estimated to be 1.09×10−9 mol cm−2, which is obviously larger than the reported values of 4.81×10−10 mol cm−2 on multi-walled carbon nanotubes modified graphite electrode (MWCNTs/GRE) [33], 3.7×10−10 mol cm−2 on poly(acid yellow 9)/nano-TiO2 modified glassy carbon electrode (PAY/nano-TiO2/GCE) [34]. This large surface adsorption amount might also be one of the reasons to enhance the electrochemical response of ACOP on GR–CS/GCE. 3.3. Optimization of experimental conditions 3.3.1. Influence of the amount of GR–CS The influence of the cast amount of GR–CS on the electrochemical behaviors of ACOP was first investigated. The results show that the redox peaks increase as the coated amount of GR–CS increased in the range from 0 to 10 μL. However, when the amount exceeds 10 μL, the redox peaks show slight decrease, which can be ascribed to the reason that the large film thickness hampers the electron transfer of the sensor. On the other hand, if the modified amount of GR–CS is too large, the film will be easily shed from the electrode surface, and meanwhile the large background makes the signal/noise (S/N) ratio very small. Therefore, taking into consideration the stability of the film and the S/N ratio comprehensively, 10 μL of GR–CS suspension was applied for fabricating the sensor.

M. Zheng et al. / Materials Science and Engineering C 33 (2013) 1514–1520

3.3.3. Influence of the accumulation potential and accumulation time Accumulation treatment is a simple and effective way to enhance the sensitivity in electrochemical analysis [35,36]. In this work, it is observed that the accumulation potential (Ea) and the accumulation time (ta) also have large impacts on the electrochemical response of ACOP. The results suggest that when Ea was set as 0.2 V, the redox peak currents increase with the accumulation time and reach the

d

Ep/V

0.8 0.6 0.4

a c b

0.2 0

3

5

7

9

pH

I/10-4A

3.3.2. Influence of the concentration and pH values of B–R The concentration of B–R buffer also has great effects on the electrochemical responses of ACOP. It is found that when the concentrations of B–R are increased from 8 mM to 40 mM, the redox peaks of ACOP increase and the ΔEp decreases gradually (Fig. 3), suggesting that ACOP has better electrochemical reaction at the high concentration of supporting electrolyte. When the concentration of B–R buffer is larger than 40 mM, the peak currents and the ΔEp values are hardly changed. Therefore, 40 mM B–R was adopted in this work. It has been frequently reported that the acidity had significant effects on the electrochemical response of ACOP [9,11]. In this work, the influence of acidity of the B–R buffer on the electrochemical responses of ACOP was also investigated, and the results are depicted in Fig. 4. It is clearly observed that when the acidity of B–R buffer is changed from pH 4.0 to 9.0, the redox peaks also varied accordingly, and the largest redox peaks were obtained at pH = 7.0. Therefore, pH = 7.0 was chosen as the optimal acidity in this work. In addition, both the anodic and the cathodic peak potentials (Epc) shift negatively with the increase of pH values, indicating that the proton transfer process is involved in the electrochemical reaction of the drug. Inset of Fig. 4 shows the linear relationships of oxidation peak potential (Epa), reduction peak potential (Epc) and the formal potentials (E 0) with the pH values. From the regression equation of E 0 with pH, E 0/V = 0.7929 − 0.0621 pH (r = 0.9957), the slope value of 62.1 mV pH −1 is very close to the Nernstian theoretical value of 59 mV pH −1, showing that the loss of electrons is accompanied by the loss of an equal number of protons. As the electron transfer number (n) of ACOP has been proved to 2 [9,29,33], therefore the proton numbers intervening in the redox process can also be calculated approximately to be 2. In addition, it has been reported that the redox process of ACOP at electrode is a quasi-reversible reaction, which produces the unstable oxidized product N-acetyl-p-quinoneimine (NAPQI) [33,34]. Thus according to the calculated numbers of protons and electrons that are involved in the electrochemical reaction, the redox mechanism of ACOP can be illustrated as Scheme 1.

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f a

E/V(vs. Ag/AgCl/3 M KCl) Fig. 4. CVs of 1.0 × 10−4 M ACOP in 40 mM B–R at pH values of 4.0 (a), 5.0 (b), 6.0 (c), 7.0 (d), 8.0 (e) and 9.0 (f). Inset: plots of Epa (a), Epc (b) and E0 (c) vs. pH.

maximum value at 200 s. The accumulation potential experiments show that when the potentials are changed from − 0.7 to 0.8 V, a maximum peak is obtained at 0.2 V. Therefore, 200 s and 0.2 V were chosen as the optimal pre-accumulation conditions for electroanalysis of ACOP in this work.

3.4. Electron-transfer kinetic parameters The electro-transfer kinetic parameters such as the electron transfer coefficient (α) and the standard electron transfer rate constant (ks) of ACOP on the modified electrode were further investigated through varying scan rates (v). Fig. 5 shows the dependence of CVs of ACOP on the scan rate. It is found that the redox peak currents increase linearly with v in the range from 10 to 300 mV s − 1 (inset), demonstrating an adsorption-controlled process of ACOP on GR–CS/GCE. The linear regression equations for the anodic and the cathodic peak currents are Ipa/μA = − 166.40 v/(V s − 1) − 7.28 and Ipc/μA = 123.21 v/(V s − 1) + 5.88 with the correlation coefficients (r) of 0.9902 and 0.9753, respectively. The slope of the linear equation for the oxidation peak is 1.4 fold larger than that of the reduction peak, suggesting that the modified electrode possesses the higher electrocatalytic activity toward the oxidation process than the reduction process, which may be due to the surface accumulation of ACOP [33].

a I/10-5A

OH

O +

NH

E/V(vs. Ag/AgCl/3 M KCl) Fig. 3. CVs of 1.0×10−4 M ACOP in 8 mM (a), 20 mM (b), 32 mM (c) and 40 mM (d) B–R (pH 7.0) buffer solution.

2H+ + 2e-

N

O C CH3

O C CH3

ACOP

NAPQI

Scheme 1. Electrochemical oxidation mechanism of ACOP.

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M. Zheng et al. / Materials Science and Engineering C 33 (2013) 1514–1520 1.6

a

0.4

Q/µC

Ep/V

0.6

b

0.2 0 -1.6

-1.2

-0.8

Q/10-4C

I/10-4A

0.38 0.41 0.44 0.47 0.50 0.53 1/2

(t/s)

t/s

E/V(vs. Ag/AgCl/3 M KCl) Fig. 6. CC response of 1.0 × 10

Additionally, the relationships of the redox peak potentials with the scan rate were applied to calculate the electrochemical parameters with the following Laviron's equations [37]:

0′

ð3Þ

Epc ¼ E −2:3RT=αnF logv

ð4Þ

logks ¼ α logð1−α Þ þ ð1−α Þ logα− logðRT=nF Þ−ð1−α ÞαnFΔEp =2:3RT:

ð5Þ

The linear relationships between the Epa and Epc with the log v were established to be Epa/V = 0.1755 log v/(V s −1) + 0.6381 (r = 0.9758) and Epc/V = − 0.0853 log v/(V s −1) + 0.1651 (r = 0.9579) (inset in Fig. 5). Then according to Eqs. (3) and (4), the values of α and n were calculated to be 0.67 and 1.9, respectively. Further, based on Eq. (5), the value of ks was calculated to be 0.25 s −1.

−4

M ACOP on GR–CS/GCE. Inset: Plot of Q versus t1/2.

3.6. Analytical performance Under the optimized experimental conditions, the quantitative analysis of ACOP was carried out by the fabricated sensor. Since a large capacitive current existed in CV measurements, the differential pulse voltammetry (DPV) was applied in this assay because its charging current contribution to the background current is quite low. Fig. 7 shows the dependence of the DPV oxidation peaks on the concentrations of ACOP ([ACOP]). It is found that with the increase of the ACOP concentrations, the DPV oxidation signals enhance gradually, and an excellent linearity is observed over a wide concentration range from

A a I/10-5A

Fig. 5. CVs of 1.0 × 10−4 M ACOP in 40 mM B–R at different scan rates (from inner to outer):10, 30, 50, 80, 100, 150, 200, 250, and 300 mV s−1. Inset: the relationships of Epa (a) and Epc (b) with log v.

0′

1.2 1.0

-0.4

log (v/Vs-1)

Epa ¼ E þ 2:3RT=ð1−α ÞnF logv

1.4

i

3.5. Calculation on the diffusion coefficient The chronocoulometry (CC) method was applied to determine the diffusion coefficient (D) of ACOP on GR–CS/GCE, according to the formula given by Anson [38]:

E/V(vs. Ag/AgCl/3 M KCl)

B

0 Q ¼ 2nFA0 ðDt Þ

=π

1=2

þ Q dl þ Q ads

ð6Þ

where Qdl is the double-layer charge; and Qads is the Faradaic charge ascribing to the oxidation of the adsorbed ACOP. Qdl was assumed not changed in the presence and absence of ACOP in our experiments. Fig. 6 shows the CC curve (Fig. 6) and the corresponding Q ~ t 1/2 curve (inset of Fig. 6) of 1.0 × 10 −4 M ACOP on GR–CS/GCE. It is clear that the Q values showed a good linearity with t 1/2, Q/μC = 357.43 (t/s) 1/2 − 22.88 (r = 0.9988). From the slope of Q ~ t 1/2 and the obtained values of A0 and n, the D value was calculated to be 3.61 × 10 −5 cm 2 s −1, which is about one-order larger than the values reported on carbon-coated nickel magnetic nanoparticles modified GCE (4.97 × 10 −6 cm 2 s −1) [29], cadmium pentacyanonitrosylferrate modified GCE (4.25 × 10 −6 cm 2 s −1) [39], and comparable to the value of 5.83 × 10 −5 cm 2 s −1 on cobalt oxide nanoparticles modified carbon ceramic electrode [40].

-2

Ipa/µA

1=2

-4 -6 -8

-10

0

25

50

75

100

[ACOP]/µM Fig. 7. (A) DPVs of 0 (a), 2.5×10−6 M (b), 5.0×10−6 M (c), 7.5×10−6 M (d), 1×10−5 M (e), 2.5×10−5 M (f), 5×10−5 M (g), 7.5×10−5 M (h), and 1.0×10−4 M (i) ACOP in 40 mM pH 7.0 B–R on GR–CS/GCE. (B) Linear relationship between Ipa and the concentrations of ACOP ([ACOP]).

M. Zheng et al. / Materials Science and Engineering C 33 (2013) 1514–1520

1.0 × 10 −6 M to 1.0 × 10−4 M, Ipa/μA =−0.079 [ACOP]/μM − 0.4486 (r = 0.9894) (inset of Fig. 7). Based on the signal-to-noise ratio (S/N) of 3, the detection limit was estimated to be 3.0 × 10 −7 M. Referring to the analytical performances of some recently published reports (Table 1), it is found that the obtained detection limit in this work is somewhat higher than that on PANI-MWCNT modified electrode [9], which is likely related to the fact that both PANI and MWCNTs have high electrocatalytic and surface area effects. But, compared with the electrode modified with the other materials like C-Ni, MWCNTs, PAY/ nano-TiO2 and C60, our developed method shows the lower detection limit and the wider kinetic range, suggesting that the developed sensor in this work can be served as a promising platform for the sensitive detection of ACOP in low concentration. Additionally, a relative standard deviation of 2.5% for 1.0 × 10 −4 M ACOP (n = 8) suggests that the GR–CS modified electrode has good reproducibility. Six electrodes fabricated independently were used to determine 1.0 × 10 −4 M ACOP, and the relative standard deviation is 3.0%, revealing an excellent repeatability of the electrode preparation. The stability of the film electrode was evaluated by measuring the peak current of 1.0 × 10 −4 M ACOP repeatedly. It is found that after 50-times test, the peak current deviates from its original response only 3.6%. 3.7. Interference study The potential interference for the determination of ACOP was also studied. Under the optimized conditions, the oxidation peak of 1.0 × 10 − 4 M ACOP was individually measured in the presence of different concentrations of the common interferents, and then the change of peak current was checked. It is found that 1 ×10−3 M Al3+, 1 ×10−3 M Ca2+, 1 ×10−3 M Cu2+, 1× 10−3 M Fe3+, 1 ×10−3 M Cd2+, 1× 10−3 M Pd2+, 1 ×10−3 M Cl−, 1× 10−3 M NO3−, 1 ×10−3 M HPO42−, 1× 10−3 M H2PO4−, 1× 10−3 M CO32−, 1×10−3 M SO42−, 1×10−4 M ascorbic acid (AA), 1×10−4 M vitamin E (VE), 1×10−4 M −4 L-cysteine, 1×10 M uric acid (UA) and 1×10−4 M glucose, almost have no influence on the detection of ACOP since the peak current change is below 5%, revealing that this sensor has good selectivity for ACOP determination. 3.8. Recovery The method presented here was further applied to investigate the ACOP in the real samples. In our experiments, the concentration of ACOP was calculated using standard addition method. The recovered ratio on the basis of this method was investigated and the value is between 92 and 107%, as shown in Table 2, indicating that the quantitative determination of ACOP in pharmaceutical preparations using GR– CS composite modified electrode is effective and accurate. 4. Conclusions In this paper, a novel method for examining the electrochemical behaviors of ACOP was developed through using the nanocomposite material of GR–CS as the electrochemical sensing platform. Electrochemical Table 1 Comparison of analytical results of ACOP on the different sensing platforms. Modified materials

Linear working range (M)

Limit of detection (M)

References

PANI-MWCNTs C-Ni MWCNTs PAY/nano-TiO2 C60 MWCNTs GR–CS

1.0 × 10−6–1.0 × 10−4 7.8 × 10−6–1.1 × 10−4 2.5 × 10−5–4.0 × 10−4 1.2 × 10−5–1.2 × 10−4 5.0 × 10−5–1.5 × 10−3 1.5 × 10−5–2.7 × 10−5 1.0 × 10−6–1.0 × 10−4

2.5 × 10−7 6.0 × 10−7 5.0 × 10−7 2.0 × 10−6 5.0 × 10−5 1.0 × 10−5 3.0 × 10−7

[9] [29] [33] [34] [41] [42] This work

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Table 2 Results of the recovery test. Sample concentration (M)

Added amount (M)

Determined value (M)

Recovery (%)

1.0 × 10−6 1.0 × 10−6 1.0 × 10−6 1.0 × 10−6

1.4 × 10−5 3.4 × 10−5 6.4 × 10−5 9.9 × 10−5

1.6 × 10−5 3.5 × 10−5 6.0 × 10−5 9.6 × 10−5

107 100 92 96

characterization experiments showed that GR–CS/GCE possesses the advantages of high electrocatalysis, large surface area effect and good stability, which indicates that the interface of GR–CS/GCE is promising as an electrochemical sensing platform. Electrochemical sensing experiments further show that the electrochemical response of ACOP is greatly increased on GR–CS/GCE as compared with the bare GCE, which can be ascribed to the promotion of the electrochemical parameters like surface adsorption amount, electron transfer rate constant and diffusion coefficient of ACOP on GR–CS/GCE. Under the optimal conditions, a wide linear range from 1.0×10−6 to 1.0×10−4 M and a low detection limit of 1.0×10−7 M were obtained for ACOP detection. Moreover, the good anti-interference ability and the excellent regeneration and reproducibility make the sensing platform useful for the routine analysis of paracetamol in clinical samples as well as in pharmaceutical industry. Acknowledgments The work is supported by the NSFC (nos. 20805041 and 21275127), NCETFJ (no. JA12204), Science and Technology Project of SIQSAQ (no. 2011QK217), Natural Science Foundation of Fujian Province (no. 2011J01059), Key Provincial University Project of Fujian (no. JK2011032) and the Innovation Base Foundation for Graduate Students Education of Fujian Province. References [1] B.D. Clayton, Y.N. Stock, Basic Pharmacology for Nurses, Unit 3, Mosby Inc., St. Louis, 2004. [2] K.V. Blake, D. Bailey, G.M. Zientek, L. Hendeles, Clin. Pharm. 7 (1988) 391–397. [3] M.D. Teresa Rivera-Penera, M.D. Roberto Gugig, M.D. Judy Davis, M.D. Sue McDiarmid, M.D. Jorge Vargas, M.D. Philip Rosenthal, M.D. William Berquist, B. Melvin, M.D. Heyman, E. Marvin, M.D. Ament, J. Pediatr. 130 (1997) 300–304. [4] Y.N. Ni, C. Liu, S. Kokot, Anal. Chim. Acta 419 (2000) 185–196. [5] K.G. Kumar, R. Letha, J. Pharm. Biomed. Anal. 15 (1997) 1725–1728. [6] A.B. Moreira, H.P.M. Oliveira, T.D.Z. Atvars, I.L.T. Dias, G.O. Neto, E.A.G. Zagatto, L.T. Kubota, Anal. Chim. Acta 539 (2005) 257–261. [7] K.A. Johnson, R. Plumb, J. Pharm. Biomed. Anal. 39 (2005) 805–810. [8] M. Boopathi, M.S. Won, Y.B. Shim, Anal. Chim. Acta 512 (2004) 191–197. [9] M.Q. Li, L.H. Jing, Electrochim. Acta 52 (2007) 3250–3257. [10] F.A. Nada, F.E.K. Maher, Talanta 79 (2009) 639–647. [11] M. Houshmand, A. Jabbari, H. Heli, J. Solid State Electrochem. 12 (2008) 1117–1128. [12] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Science 306 (2004) 666–669. [13] A.K. Geim, K.S. Novoselov, Nat. Mater. 6 (2007) 183–191. [14] M.Y. Han, B. Özyilmaz, Y.B. Zhang, P. Kim, Phys. Rev. Lett. 98 (2007) 206805–206808. [15] Y.R. Kim, S. Bong, Y.J. Kang, Y. Yang, R.K. Mahajan, J.S. Kim, H. Kim, Biosens. Bioelectron. 25 (2010) 2366–2369. [16] J.F. Wu, M.Q. Xu, G.C. Zhao, Electrochem. Commun. 12 (2010) 175–177. [17] C.S. Shan, H.F. Yang, J.F. Song, D.X. Han, A. Ivaska, L. Niu, Anal. Chem. 81 (2009) 2378–2382. [18] Q.X. Wang, M.X. Zheng, J.L. Shi, F. Gao, F. Gao, Electroanalysis 23 (2011) 915–920. [19] L.S. Fan, J.A. Chen, S.Y. Zhu, M. Wang, G.B. Xu, Electrochem. Commun. 11 (2009) 1823–1825. [20] J. Li, S.J. Guo, Y.M. Zhai, E.K. Wang, Electrochem. Commun. 11 (2009) 1085–1088. [21] Q.X. Wang, B. Zhang, X.Q. Lin, W. Weng, Sens. Actuators, B 156 (2011) 599–605. [22] N.V. Majeti, K. Ravi, React. Funct. Polym. 46 (2000) 1–27. [23] J.J. Li, R. Yuan, Y.Q. Chai, X. Che, W.J. Li, X. Zhong, Microchim. Acta 172 (2011) 163–169. [24] Y. Liu, M.K. Wang, F. Zhao, Z.A. Xu, S.J. Dong, Biosens. Bioelectron. 21 (2005) 984–988. [25] J. Li, Q. Liu, Y.J. Liu, S.C. Liu, S.Z. Yao, Anal. Biochem. 346 (2005) 107–114. [26] Q. Xu, C. Mao, N.N. Liu, J.J. Zhu, J. Sheng, Biosens. Bioelectron. 22 (2006) 768–773. [27] Y.J. Zou, C.L. Xiang, L.X. Sun, F. Xu, Biosens. Bioelectron. 23 (2008) 1010–1016.

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