Disposable screen printed graphite electrode for the

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Disposable screen printed graphite electrode for the direct electrochemical determination of ibuprofen in surface water Sidra Amin a , M. Tahir Soomro a,b,∗ , Najma Memon a , Amber R. Solangi a , Sirajuddin a , Tahira Qureshi a , Ali R. Behzad c a

National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan Center of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80216, Jeddah 21589, Saudi Arabia c Imaging & Characterization Core Lab Research Development, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia b

a r t i c l e

i n f o

Article history: Received 28 January 2014 Received in revised form 18 June 2014 Accepted 23 July 2014 Verlicchi Paola Keywords: Ibuprofen Wastewater Square wave voltammetry Baseline correction

a b s t r a c t The potential of square wave voltammetry (SWV) for the determination of ibuprofen in aqueous solution, applying baseline correction, is reported. A screen printed graphite electrodes (SPGEs), especially pretreated for this purpose, were used to investigate the electrochemical oxidation and detection of ibuprofen. After optimization of SWV parameters, measurements were carried out at 200 Hz modulation frequency, 4 mV step potential and 40 mV pulse amplitude for the determination of ibuprofen. The surfaces of both untreated and pretreated SPGEs were characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The electro-catalytic properties of both the electrodes were correlated with the surface treatment. The pretreated screen printed graphite electrode exhibited a high sensitivity toward ibuprofen even in low concentration. The developed method was found rapid, cost-effective and reproducible for in-field ibuprofen detection. © 2014 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

1. Introduction The electrochemical sensors have gained popularity in past few decades and widely used in electroanalytical applications. The electrochemical sensors integrate the sensitivity of the electroanalytical methods with the inherent selectivity of the sensing or identifying element. The whole process of analyte recognition based on the catalytic or binding event occurs between the analyte and sensing element and eventually results in an electrochemical signal monitored by a transducer (Ronkainen et al., 2010; Kerman et al., 2004; Yogeswaran and Chen, 2008; Jubete et al., 2009). By considering its importance sensors have been already marketed products and routinely practiced in environmental, clinical and industrial applications (Stetter et al., 2003; Tagar et al., 2011). Ibuprofen (IBP) is widely used as non-steroidal antiinflammatory drug for the treatment of a variety of symptoms. Being the major constitute of the discharge of pharmaceutical industrial, domestic, and hospital wastes many reports have

∗ Corresponding author at: Center of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80216, Jeddah 21589, Saudi Arabia. Tel.: +966 548060931. E-mail addresses: [email protected], [email protected], [email protected] (M.T. Soomro).

been published regarding the detection and analytical control of ibuprofen by GC–MS, HPLC, spectrofluorometry, and electrophoresis (Ghoneim and El-Desoky, 2010; Motoc et al., 2011; Whelan et al., 2002; Hamoudová and Pospíˇsilová, 2006; Khoshayand et al., 2008; Ternes, 2001). Some other approaches are based on derivatization process (Manea et al., 2012). Almost all the methods used for the detection of ibuprofen are either costly or require expertise in handling the instruments (Chen and Shah, 2013) therefore, it is desired to develop a user friendly method for direct field applications. Electroanalytical detection based on the use of screen printed graphite electrodes for sensing of ibuprofen can offer a practically viable method free from the pretreatment of samples, prolonged analysis time and sophisticated experimental setup. Electroanalytical methods are simple, economical, rapid and sensitive to reach the lower limit of detection. Among the electroanalytical techniques, voltammetry coupled with pulse waveform (e.g., SWV) is considered a highly sensitive technique with very low detection profiles attributed to zero background current. An excellent review regarding the potential applications of square wave voltammetry is reported by Chen and Shah (Chen and Shah, 2013; Ramaley and Krause, 1969; Krause and Ramaley, 1969). The interpretation and manipulation of acquired data with various data processing options further improves the sensitivity of the method (Wang et al., 1999).

http://dx.doi.org/10.1016/j.enmm.2014.07.001 2215-1532/© 2014 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Please cite this article in press as: Amin, S., et al., Disposable screen printed graphite electrode for the direct electrochemical determination of ibuprofen in surface water. Environ. Nanotechnol. Monit. Manag. (2014), http://dx.doi.org/10.1016/j.enmm.2014.07.001

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Fig. 1. SEM images of (a) untreated SPGE and (b) pretreated SPGE.

The electroanalytical procedure reported in literature, for the determination of ibuprofen, have employed selective membrane electrode using potentiometry or silver functionalized carbon nano-fiber composite electrodes using voltammetry (Manea et al., 2012; Stefan-van Staden et al., 2009). The adopted methods require functionalization of surfaces that adds complexity to assay procedure. In contrast, screen printed electrodes (SPEs) composed of working, reference and auxiliary electrodes are developed by printing different conductive inks on various types of plastics or ceramic materials (Renedo et al., 2007; Grennan et al., 2001; Wang et al., 1998). These SPEs are also proved useful over other solid electrodes for direct and reliable field analysis of a variety of samples from different origins. The reproducibility of the results after successive use is considered as a silent feature of SPEs (Lucarelli et al., 2002a, 2002b). This work is aimed at developing a simple and sensitive electroanalytical method for the determination of ibuprofen in untreated wastewater using electrochemically pretreated screen printed graphite electrodes. The screen printed graphite electrodes, pretreated at a fixed potential, were used to carry out the square wave voltammetric investigations of the oxidation of ibuprofen in aqueous solution.

2. Materials and methods 2.1. Apparatus All voltammetric measurements were carried out by CHI 760D Electrochemical Workstations, equipped with software CHI 9.22 (Austin, USA) for data analysis, utilizing a three-electrode system assembly. The surface characterization was carried out with high resolution scanning electron microscope FEI MagellenTM 400. A glass cell equipped with gas bubbler and gas outlet ports was used for electroanalytical measurements. The number of electrodes, glassy carbon (GCE, 2 mm), platinum (PtE, 2 mm), gold (AuE, 2 mm), and modified electrode (BiGCE, 2 mm), were investigated for the determination of ibuprofen in comparison with screen printed graphite electrodes. Bismuth modified electrode was constructed at a fixed potential (−1.0 V vs. Ag pseudo reference electrode for 300 s) by immersing glassy carbon electrode (GCE) in acetate buffer system of 0.25 M containing 100 ␮g/cm3 Bi3+ ion at pH 4.7. A platinum (PT) wire as counter electrode and an Ag/AgCl reference electrode were purchased from CHI (Austin, USA) and used as received. The

screen printed graphite electrodes used in this study were purchased from CHI (Austin, USA) and consisted of 3 mm graphite working electrode, graphite counter electrode and Ag pseudo reference electrode (such as an Ag wire carries through the role of a reference electrode instead of true reference electrode). The solutions were de-aerated with nitrogen at least for 30 min. For solid electrodes, the standard procedure of electrode cleaning and mechanical polishing was applied before every measurement. A screen printed graphite electrode surface was pretreated (conditioned) by applying a fixed potential of +1.6 V for 3 min vs. Ag pseudo reference electrode. The peak current of IBP oxidation, i.e., ∼+1.1 V vs. Ag pseudo reference electrode, was measured.

2.2. Reagents and solutions Ibuprofen (IBP) drug (was provided by Birds Chemotec, Karachi, Pakistan), sodium acetate (anhydrous, MP Biomedical, LLC, France), acetic acid (Sigma Aldrich), and potassium chloride (Fisher Scientific UK Limited) were used as received. All solutions were prepared in acetate buffer with a final concentration of 0.25 M and pH 4.7. For analysis, the pH of sample solutions was maintained at 4.7 using 0.25 M acetate buffer. The wastewater samples were collected from the municipal wastewater drainage systems whereas river water samples were collected from River Indus Jamshoro. Immediately after sampling and transportation samples were preserved by storing in bottles at 4 ◦ C. Prior to measurements the particulates from waste and river water samples were removed by syringe filters (0.45 ␮m) and their pH was then adjusted to 4.7.

3. Results and discussion 3.1. SEM analysis of screen printed graphite electrodes As presented in Fig. 1(a), the SEM examination shows a rough and non-homogeneous surface of untreated SPGE. After pretreatment, the roughness of the surface significantly reduced and homogeneous pattern of arranged elongated microstructures appeared (Fig. 1(b)). In the preconditioning process, the adsorbed species are removed from the surface leaving behind the arranged oxide layer which may enhance the electron transfer reaction compared to the surface covered with adsorbed species (untreated SPGE


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3.3. Square wave voltammetric response of IBP

11600 u untreated SPGE E p ated SPG pretre GE

11400 11200 Im (Z) / Ω

3

11000 800 600 400 200 0 0

200

400

600

800 1000 Re (Z) / Ω

12000

1400

1600

Fig. 2. EIS Nyquist spectra of untreated SPGE and pretreated SPGE in 0.1 M KCl solution containing 2 mM K3 [Fe(CN)6 ].

surface). The high current response of the pretreated SPGE toward IBP than untreated SPGE supported the same premise.

3.2. Electrochemical impedance analysis of screen printed graphite electrodes

3.4. Optimization of SWV parameters for IBP determination

Electrochemical impedance spectroscopy (EIS) is a very versatile and powerful technique for characterizing charge transfer process taking place at the surface of modified and unmodified electrodes (Yun et al., 2009; Suni, 2008; Muthirulan et al., 2014). In Fig. 2 EIS Nyquist spectra of untreated SPGE and pretreated SPGE are shown. The EIS Nyquist spectra usually include two parts, semicircular and linear. A semicircular part which is located at higher frequencies reflects the charge transfer process (faradaic process) whereas linear part positioned at lower frequencies is characteristic to the diffusion process (Muthirulan et al., 2014). The untreated SPGE shows a small semicircle indicating a slow charge transfer rate. However, upon pretreatment of the SPGE the semicircle or charge transfer resistance nearly disappeared and suggesting that the charge transfer become easier with the pretreated SPGE electrode. These results are also in complete agreement with the SEM results and confirming that the pretreated SPGE has low charge transfer resistance compared to untreated SPGE electrode.

The optimization of square wave voltammetric parameters for determination of IBP in water, with pretreated screen printed graphite electrodes, was also carried out and illustrated in Fig. 4. The results show significant influence of square wave voltammetric parameters on the oxidation current of IBP. The current response of IBP increased linearly with the frequency up to 200 Hz (Fig. 4(b)) and beyond 200 Hz signal noises were introduced in IBP signal. The peak shape and current response for IBP were also greatly affected by varying the amplitude and step potential values. Thus, for determination of IBP the optimal values of square wave voltammetric parameters were found to be: frequency 200 Hz; amplitude 40 mV; step potential 4 mV.

3.5. Optimization of pH The square wave voltammograms of IBP detection in 0.25 M acetate buffer containing 10 ␮g/cm3 IBP with the pH values varying 60

(a)

130

(b) 50

110

PtE AuE GCE SPGE Bi/GCE

70

40

Current / µA

90 Current / µA

The electrochemical response of IBP on various electrodes such as AuE, PtE, GCE, and Bi3+ modified GCE is presented in Fig. 3(a). The Pt electrode has an excellent potential as a catalyst for water oxidation and therefore the IBP response hidden by the background decomposition current of water. The finding is in accordance with the literature (Brooks and Richter, 2002). The surface oxidation of Au electrode limits its use in the positive potential (Zoski, 2007) while using both GC and Bi3+ modified GC electrodes, well defined oxidation peak of IBP are hard to resolve (Merkoçi et al., 2010; ˇ Svancara et al., 2010). The square wave voltammograms, for oxidation of IBP in water, were recorded using untreated and pretreated screen printed graphite electrodes and are illustrated in Fig. 3(b). The oxidation peak of IBP obtained with untreated SPGE is poorly defined, because of water decomposition current (Bard and Faulkner, 2001), and does not facilitate quantitation of IBP at very low concentration. However, a well defined oxidation peak of IBP with significantly improved current is achieved with pretreated SPGE. Further, enhancement of the oxidation peak of IBP, using appropriate baseline correction method(s) associated with background subtraction and suitable computer program, permits quantitation of IBP in water.

50

pretreated SPGE untreated SPGE Blank

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Fig. 3. (a) Oxidation current responses of IBP determination recorded using different electrodes. (b) Oxidation of ibuprofen (10 ␮g/cm3 IBP, red) with pretreated SPGE. The oxidation peak of IBP is around +1.1 V vs. Ag pseudo reference. Blank (blue) recorded in 0.25 M acetate buffer of pH 4.7. Note that the oxidation peak of IBP with untreated SPGE (green) at +1.13 V vs. Ag pseudo reference. Square wave voltammetric parameters: frequency 200 Hz, amplitude 40 mV, step potential 4 mV.


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40 50 Amplitutde / mV

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Fig. 4. Effect of the square wave parameters on the IBP oxidation peak. The peak current and peak area of IBP signal depends on (a and b) frequency, (c) amplitude, and (d) step potential. The optimal value of each parameter was obtained.

from 3.0 to 6.0 is recorded and shown in Fig. 5. It was noted that the current responses and the peak potential of IBP significantly change with increasing pH from 3.0 to 6.0. A decrease in the response of IBP with increasing pH revealed that the detection of IBP is feasible only in the acidic medium as no response of IBP oxidation was detected in basic medium with the pretreated screen printed graphite electrode. Based on the peak response, pH 4.7 was selected for the identification of IBP in the aqueous medium.

3.6. Baseline correction for IBP determination The oxidation response of IBP obtained with pretreated SPGE is previously shown in Fig. 3(b). Although the current response of IBP on pretreated SPGE is well defined as compared to other electrodes (Fig. 3), however to achieve trace determination of IBP in water (wastewater) a baseline correction was applied. Fig. 6 represents a comparison of conventional square wave voltammogram of IBP determination with blank subtracted (blue)

Blank substracted (12 μA) Baseline corrected (9 μA) Ibuprofen (18 μA)

60 50

Current / μA

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Fig. 5. Square wave voltammograms of 10 ␮g/cm3 IBP containing 0.25 M acetate buffer at different pH. All other conditions are same as in Fig. 1.

0.4

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1.0

1.2

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E/V Fig. 6. Square wave voltammetric signal of 10 ␮g/cm3 IBP at SPGEs. Electrolyte 0.25 M acetate buffer (pH 4.7). Original voltammogram (black), blank subtracted (blue), and baseline corrected (red).


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Table 1 Precision (intra-and inter-day) in standard solutions of IBP. Concentration (␮g/ml)

Intra-day (n = 5)

Inter-day (n = 15)

Mean response, ␮A ± SD

RSD (%)

Mean response, ␮A± SD

RSD (%)

8.014 ± 0.445 9.165 ± 0.368 11.844 ± 0.467

4.319 4.017 3.945

8.101 ± 0.350 9.275 ± 0.506 11.601 ± 0.562

4.322 5.454 4.842

6 8 10

Current / μA

9.8

a

Current / μA

3

10 µg/cm 3 8 µg/cm 3 6 µg/cm 3 4 µg/cm 3 2 µg/cm

b

1.304

4.65 ± 0.53

4.30 ± 0.59

7.4 0.0

5.1

3

0.6

1.2

1.1

0.0

0.6

1.2

E/V Fig. 9. Baseline corrected square wave voltammograms for oxidation of IBP in (a) wastewater and in (b) river water.

0.00.61.2

0.00.61.2

0.00.61.2

0.00.61.2

0.00.61.2

E/V Fig. 7. Baseline corrected square wave voltammetric response of different concentrations of IBP on pretreated screen printed graphite electrodes.

and baseline corrected (red) voltammograms. All three voltammograms are superimposed on each other. Blank subtraction and baseline corrections analysis were performed using several graphing software’s (not reported here). We found that the user defined baseline correction mode in OriginPro 8 Software is an efficient and flexible way to eliminate background contribution and produce a well defined IBP oxidation peak of IBP. Noticeably different current scales were observed for all three voltammograms as shown in Fig. 6. Therefore, baseline corrected voltammograms of IBP allows us to obtain significantly improved quantitation of IBP in water (effluent). The calibration was made using the baseline corrected square wave voltammograms of IBP shown in Fig. 7. The calibration plot between the current recorded (vs. Ag pseudo reference electrode) and the various concentrations of IBP is represented in Fig. 8. Linear dependency of the recorded current was observed vs. IBP concentration but at further lower concentration, sensitivity was lost. However, to see the effectiveness of the method, instrumental detection limit and quantification limit were calculated and found to be, LOD = 1.3 ␮g/cm3 [3.3 (standard error in 10

Peak Current (μA) / (1e-6)

y = 0.9277x - 0.2652 R² = 0.9964 8

6

4

2

0 0

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6 Conc. (μg/cm3)

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10

12

Fig. 8. Linear relation observed between peak current (ip ) vs. concentration of IBP.

b/slope)], LOQ = 3.9 ␮g/cm3 [10 (standard error in b/slope)]. Using pretreated SPGE, detection limits were improved 12.5 times to instrumental detection limits, thereby, LOD of 0.1 ␮g/cm3 and LOQ of 0.312 ␮g/cm3 were achieved. 3.7. Reproducibility The reproducibility and precision of the method for determination of IBP was measured by performing the analysis at different time intervals ranging from hours to days. Three different concentrations of 6 ␮g/cm3 , 8 ␮g/cm3 , and 10 ␮g/cm3 were selected from the linear range. The response of IBP was recorded 5 times in a day for three consecutive days. The precision of the method was evaluated in terms of RSD (%) and the results are presented in Table 1. The results indicate that the method is consistent within the error limit and effective for determination of IBP in water. The reliability of the proposed method was also established by recovery studies. Two sample concentrations of 0.2 and 0.5 ␮g/cm3 were selected and pre-concentrated by extraction procedure. The % recovery was calculated by comparing the IBP signal of pre-concentrated samples with standard samples and obtained as 96% and 106%, respectively. 3.8. Analysis of real samples The waste and river water samples were filtered before analysis and tested using screen printed graphite electrode for determination of IBP. The baseline corrected square wave voltammograms are presented in Fig. 9. The concentration of IBP found in a wastewater sample was 0.266 ␮g/cm3 whereas in river water it was 0.283 ␮g/cm3 . The results revealed that the presence of IBP in environmental water intimated that the possible reason for the presence of IBP in water samples could be because of the release of untreated wastes from pharmaceutical industry, hospitals and houses effluent into the surroundings. IBP is rated as one of the high risk pharmaceuticals that has a potential of exo-toxicity and its exposure could be harmful for human health (Escher et al., 2011; Ort et al., 2010). To make sure obtained results are meaningful they were compared with the results obtained from treated wastewater originating from hospital wastes. The concentration of IBP found in our samples is rather higher than the results as described in the above cited references and that is because we have tested untreated wastewater for IBP determination.


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4. Conclusion Pretreated screen printed graphite electrode with higher electrocatalytic activity shows efficient sensing for IBP determination. The use of pretreated SPGEs for determination of IBP is a very simple approach as it does not require any fabrication therefore overcomes the problem associated with the time consuming electrode modification processes and also provide fast, economically cheap and easy to evaluate analysis of presence of IBP in wastewater. The results also showed that the square wave voltammetric response of IBP significantly enhanced after applying baseline correction. For detection and determination of IBP, the developed method is practical and competitive in terms of sensitivity along with analysis cost, time and also provides possibility to develop screening test for in-field analysis. Acknowledgement Dr. Muhammad Tahir Soomro acknowledges the funding offered by Higher Education Commission, Islamabad, Pakistan as interim placement to stay and work at National Centre of Excellence in Analytical Chemistry, University of Sindh, Pakistan. References Bard, A., Faulkner, L., 2001. Electrochemical Methods: Fundamentals and Applications, 2nd Ed. Wiley, New York. Brooks, S.C., Richter, M.M., 2002. Determination of DNA bases using electrochemistry: a discovery-based experiment. Chem. Ed. 7, 9–13. Chen, A., Shah, B., 2013. Electrochemical sensing and biosensing based on square wave voltammetry. Anal. Method 5, 2158–2173. Escher, B.I., Baumgartner, R., Koller, M., Treyer, K., Lienert, J., McArdell, C.S., 2011. Environmental toxicology and risk assessment of pharmaceuticals from hospital wastewater. Water Res. 45, 75–92. Ghoneim, E.M., El-Desoky, H.S., 2010. Electrochemical determination of methocarbamol on a montmorillonite-Ca modified carbon paste electrode in formulation and human blood. Bioelectrochemistry 79, 241–247. Grennan, K., Killard, A.J., Smyth, M.R., 2001. Physical characterizations of a screenprinted electrode for use in an amperometric biosensor system. Electroanalysis 13, 745–750. Hamoudová, R., Pospíˇsilová, M., 2006. Determination of ibuprofen and flurbiprofen in pharmaceuticals by capillary zone electrophoresis. J. Pharm. Biomed. Anal. 41, 1463–1467. Jubete, E., Loaiza, O.A., Ochoteco, E., Pomposo, J.A., Grande, H., Rodriguez, J., 2009. Nanotechnology: a tool for improved performance on electrochemical screenprinted (bio)sensors. J. Sensors 2009, 1–13. Kerman, K., Kobayashi, M., Tamiya, E., 2004. Recent trends in electrochemical DNA biosensor technology. Meas. Sci. Technol. 15, R1–R11. Khoshayand, M.R., Abdollahi, H., Shariatpanahi, M., Saadatfard, A., Mohammadi, A., 2008. Simultaneous spectrophotometric determination of paracetamol, ibuprofen and caffeine in pharmaceuticals by chemometric methods. Spectrochim. Acta Mol. Biomol. Spectrosc. 70, 491–499.

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