Cobalt Flower-like Nanostructure as Modifier for Electrocatalytic

Article pubs.acs.org/IECR

Cobalt Flower-like Nanostructure as Modifier for Electrocatalytic Determination of Chloropheniramine Mandana Amiri,*,† Mohsen Alimoradi,‡ Khadijeh Nekoueian,‡ and Abolfazl Bezaatpour† †

Department of Chemistry, University of Mohaghegh Ardabili, Ardabil, Iran Department of Chemistry, Payame Noor University (PNU), Ardabil, Iran

‡

S Supporting Information *

ABSTRACT: In this approach, flower-like cobalt with a hierarchical structure was applied as modifier for voltammetric determination of chlorpheniramine, which is an antihistaminic drug. The flower-like cobalt nanostructures were synthesized by using a simple chemical method. They have been characterized by using scanning electron microscopy and cyclic voltammetry. The carbon paste electrode modified with cobalt nanostructures shows an excellent electrocatalytic activity and sensitivity toward chlorpheniramine due to its unique properties such as high specific surface area and large pore volume. Potential sweep rate and pH effects on the response of the electrode for the oxidation of chlorpheniramine were investigated. Differential pulse voltammetry has been applied for quantitative determination of chlorpheniramine. A dynamic linear range was obtained in the range of 1.0 × 10−7−1.0 × 10−5 mol L−1, and the detection limit was estimated to be 8.0 × 10−8 mol L−1.

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INTRODUCTION Chlorpheniramine or chlorphenamine is a first-generation alkylamine antihistamine which is used in the prevention of the symptoms of allergic conditions such as rhinitis and urticaria (Scheme 1).1 Several methods have been reported for

In recent years, metal nanostructures such as cobalt, nickel, and iron, and so forth have attracted attention in electroanalysis because of their unusual physical and chemical properties. Metal nanostructures-modified electrodes usually exhibit high electrocatalytic activities toward compounds with sluggish redox processes at bare electrodes. Cobalt nanostructures have been used as a modifier for the determination of thioridazine,18 nitrite,19 and arsenic(III)20 recently. Several cobalt nanostructures with various morphologies such as nanoparticles, nanorods, nanocubes, nanowires, flowers, hollowspheres, nanoboxes, and porous structures have been synthesized by means of various routes. They have attracted special interest because of their potential applications as sensors, heterogeneous catalysts, electrochromical devices, and magnetic materials.21−25 In this approach we attempt to synthesis flower-like cobalt with a hierarchical structure with high specific surface area and large pore volume for the application in sensors, simply. They have been applied as a modifier in a carbon paste electrode for voltammetric determination of chlorpheniramin using differential pulse voltammetry (DPV). This modified electrode also was applied as a sensitive sensor for the determination of chlorpheniramin in synthetic serum and pharmaceutical preparations.

Scheme 1. The Structure of Chlorpheniramine

the determination of chlorpheniramine maleate including spectrophotometry,2 liquid chromatography,3 mass spectrometry,4 gas chromatography.5 These methods are time-consuming, solvent-usage intensive, and require expensive devices and maintenance. Electrochemical methods have attracted much interest as sensors due to the high sensitivity and desirable selectivity in their responses. Compared to other mentioned analytical techniques, electrochemical methods are simple, inexpensive, and easy to use. There are just few reports for the determination of chlorpheniramine by using electrochemical methods.6−9 Over the past five decades, carbon paste, that is, a mixture of carbon (graphite) powder and a binder (pasting liquid), has become one of the most popular electrode materials used for the laboratory preparation of various electrodes, sensors, and detectors. Such a position is undoubtedly the result of optimal constellation of physicochemical and electrochemical properties of this carbon-like substrate.10 The carbon paste electrodes have great compatibility with chemical modification. They can be modified by using various electron transfer mediators such as nanomaterials,11,12 metal complexes,13,14 zeolites,15 and organic compounds.16,17 © 2012 American Chemical Society

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EXPERIMENTAL SECTION Instrumentation. Voltammetric experiments were performed with a Metrohm Computrace voltammetric analyzer model 797VA. A conventional three-electrode system was used with a carbon-paste working electrode (unmodified or modified), a saturated Ag/AgCl as reference electrode and a

Received: Revised: Accepted: Published: 14384

June 25, 2012 September 5, 2012 October 16, 2012 October 29, 2012 dx.doi.org/10.1021/ie3016736 | Ind. Eng. Chem. Res. 2012, 51, 14384−14389

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Figure 1. SEM images of cobalt nanostructures: (A) low magnification image; (B) larger magnification image.

Pt wire as the counter electrode. A digital pH/mV/Ion meter was applied for the preparation of the buffer solutions, which were used as the supporting electrolyte in voltammetric experiments. The scanning electron microscope (SEM) images were obtained using LEO 1430VP. Chemicals. Chlorpheniramine reference was kindly provided by Darou Pakhsh Pharmaceutical Company (Tehran, Iran). Stock solutions of chlorpheniramine were freshly prepared as required in 0.10 M phosphate or acetate buffer at the desired pH and protected from light during investigation. D,L-Alanine, L-arginine, glycine, L-histidine, L-phenylalanine, D,Ltryptophan, L-cysteine, citric acid, sodium chloride, and bicarbonate sodium for preparation of synthetic human serum and other reagents were purchased from Merck and were of analytical-reagent grade. All aqueous solutions were prepared with doubly distilled deionized water. Voltammetric experiments were carried out in the buffered solutions, deoxygenated by purging the pure nitrogen. Deionized and filtered water was taken from a Millipore water purification system. Preparation of Cobalt Nanostructures. The cobalt nanostructures were synthesized using a direct reduction method. Cobalt chloride as a precursor, citric acid as a weak surfactant, and sodium borohydride as a reducing agent were used. Cobalt chloride (CoCl2·6H2O) was dissolved in 1 mL of deaerated, deionized water to produce a 0.4 M solution. Then, citric acid was added to prepare 0.25 mM solution. Then, 100 mL of 0.01 M sodium borohydride (NaBH4) was gradually added in an ultrasonic bath to allow rapid mixing at the room temperature. The solution rapidly changed from pink to gray as the cobalt nanostructures were produced. The cobalt nanostructures were collected using a centerfusion and washed with distilled water and dried under vacuum for 48 h. The nanostructures in the form of powder were characterized by using scanning electron microscopy (SEM) and electrochemical methods. Preparation of Modified Carbon Paste Electrode. The unmodified carbon paste electrode (UCPE) was prepared by mixing graphite powder with an appropriate amount of mineral oil (Nujol) and thorough hand mixing in a mortar and pestle, and a portion of the composite mixture was packed into the end of a plastic tube (ca. 2.5 mm i.d.). Electrical contact was made by forcing a copper wire down the plastic tube and into the back of the composite. The modified electrode (MCPE)

was prepared by mixing unmodified composite with Co nanostructure powder (2, 5, and 10% w/w) and then homogenizing by dissolving in dichloromethane. The mixture was stirred until all the solvent evaporated. The modified composite was then air-dried for 24 h and used in the same way as the unmodified electrode.

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RESULTS AND DISCUSSION Scanning Electron Microscopic Studies. The general morphology of the cobalt nanostructures synthesized via the direct reduction route is shown in Figure 1. It is obvious from the low magnification image (Figure 1A) that most structures consist of the flower-like hierarchical structures with a size of 1−2 μm. The larger magnification image (Figure 1B) shows that these are hierarchical and composed of large numbers of nanosheets with smooth surfaces. The observed nanosheets are 400−500 nm in size and 20−30 nm in thickness and are built in flower-like hierarchical spheres. It is worth noting that by using a simple way, the flower-like hierarchical spheres were obtained. Cyclic Voltammetric Results and Microscopic Area Calculation. The microscopic areas of the modified and the unmodified carbon paste electrode were obtained by the cyclic voltammetry using K3Fe(CN)6 as a probe at different potential scan rates. For a reversible process, the following Randles− Sevcik formula is used:25 i p,a = 2.69 × 105n2/3ACoDo1/2υ1/2

(1)

Here, ip,a refers to the anodic peak current, n is the electron transfer number, A is the microscopic surface area of the electrode (cm2), DO is the diffusion coefficient (cm2 s−1), CO is the bulk concentration of K3Fe(CN)6 (mol cm−3), and ν is the scan rate (V s−1). The microscopic areas can be calculated from the slope of the plot of ip,a versus ν1/2. For 1 mM K3Fe(CN)6 in 0.1 M KCl electrolyte (n = 1 and DO = 6.7 × 10−6 cm2 s−1), the electrode surface area of the modified electrode was 1.296 cm2, and for the unmodified electrode it was 0.1645 cm2. This shows that the microscopic area of the modified electrode increased significantly. It is more than eight times larger than the microscopic area of the unmodified electrode. Voltammetric Study of Chlorpheniramine. Figure 2 exhibits voltammetric behavior of 1 mM chlorpheniramine in 0.1 M phosphate buffer solution pH 2.0 at the surface of 14385

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investigated using cyclic voltammetry. Four electrodes containing different amounts of cobalt nanostructures (0, 2.0, 5.0, and 10.0% w/w) were prepared and tested for voltammetric responses. Maximum peak current and Δi (difference between peak current of electrode in the presence and in the absence of chlorpheniramine) were obtained for 5.0% cobalt nanostructures in the paste. In higher concentrations (>5.0%) the signal decreases. This could be related to reducing the amount of graphite as conductive component or the nonhomogeneity of the paste. The Effect of pH. The voltammetric investigations were performed in the pH range between 2.0 and 7.0 in a solution containing of chlorpheniramine 1 mM using MCPE. As can be seen in Figure 3A, the maximum peak current was obtained at pH 2.0. It can be concluded that the catalytic role of cobalt nanostructure in acidic solutions of chlorpheniramine (pH 2.0) can be considered an important agent for an improvement of the electrochemical responses of chlorpheniramine. So, the phosphate buffer solution of pH 2.0 was selected as the supporting electrolyte for the quantification of chlorpheniramine. The plot of Ep,a vs pH has a slope of −49.7 mV with a correlation coefficient (R2) of 0.997 (Figure 3B). As it can be seen, a negative shift in the anodic peak has occurred by increasing the pH of the buffer solution. This confirms that H+ participates in the oxidation process in the electro-oxidation chlorpheniramine. The Effect of Scan Rate. The cyclic voltammetric studies for 1 mM chlorpheniramine were performed at the surface of the MCPE in a buffered solution of pH 2.0 at different potential sweep rates. Figure 4A exhibits the cyclic voltammograms of chlorpheniramine at the surface of MCPE with various scan rates, ν, in the range of 10−200 mV s−1. For chlorpheniramine, no cathodic peak is observed on the reverse scan in various potential sweep rates. Such a behavior confirms a catalytic EC mechanism, where a coupled irreversible chemical reaction hindered the electron transfer step. The anodic peak current varied linearly with the square root of the scan rate (Figure 4B), suggesting that the chlorpheniramine oxidation follows a diffusion controlled mechanism. The following equation can be expressed:

Figure 2. Cyclic voltammograms in the absence (MCPE, dashed line) and in the presence of 1 mM chlorpheniramine at the surface of a modified carbon-paste electrode with Co nanostructure 5% w/w (MCPE, solid line) and unmodified electrode (UCPE, dotted line), in 0.1 M phosphate buffer solution of pH 2, scan rate, 100 mV s−1.

unmodified electrode (UCPE, dotted line) and 5% w/w (MCPE, solid line) cobalt nanostructures. The dashed line exhibits the voltammetric response of MCPE in the absence of chlorpheniramine. As can be seen, there is no voltammetric peak for chlorpheniramine at the surface of UCPE in buffer solution. There is a peak current for the MCPE in 0.1 M phosphate buffer pH 2.0 which is related to oxidation of cobalt nanostructures. Comparing the MCPE response in the presence and absence of chlorpheniramine shows the signal increase in the presence of chlorpheniramine and shifts to more positive potential near 50 mV. This well-defined anodic wave with a large peak current that appears at a peak potential of −0.15 V using the MCPE can be applied for analytical measurement of chlorpheniramine. The kinetics of electron transfer improves remarkably at the surface of MCPE. The effective catalytic role of the modified electrode toward chlorpheniramine oxidation can be attributed to electrocatalytic activity of cobalt in the paste matrix. In addition to the electrocatalytic effect of cobalt nanostructures, the unique properties of the MCPE such as the high specific surface area and large pore volume enhanced the signal. The influence of the amounts of modifier on the response of the electrode was

Figure 3. (A) Cyclic voltammograms of 10−3 M chlorpheniramine at the surface of MCPE immersed in 0.1 M phosphate buffer solution pH 3, 6, and 7, 0.1 M acetate buffer pH 4 and 5, scan rate 100 mV/s; (B) variation of anodic peak potential vs various pH values in1 mM chlorpheniramine. 14386

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Figure 4. (A) Cyclic voltammograms for oxcidation of chlorpheniramine at the surface of MCPE immersed in buffer solution pH 2.0 at various scan rates: 10, 20, 40, 60, 80, 100, 150, and 200 mV/s; (B) dependence of oxidation peak current on the square root of scan rate.

Figure 5. (A) Differential pulse voltammograms (50 mV pulse amplitude, 5 mV step potential) for the oxidation of chlorpheniramine in phosphate buffer solution pH 2.0 at MCPE (bottom to top: 1.0 × 10−7, 3.0 × 10−7, 5.0 × 10−7, 8.0 × 10−7, 1.0 × 10 −6, 1.0 × 10−5 M); (B) plot of the peak current in differential pulse voltammetry versus the chlorpheniramine concentration (1.0 × 10−7 to 1.0 × 10−5 M).

tertiaryamine in its molecular structure, it presents as basic center with the availability of nonbonding electron as donor. Therefore, we may assume that the oxidation step of chlorpheniramine is located on the tertiary amine. Chlorpheniramine loses an electron from the aliphatic tertiary amine to form a cation radical, which looses a proton and electron in subsequent steps to form a quaternary Schiff base. Thus the resulted quaternary Schiff base was rapidly hydrolyzed to the 5chloro-2-(methylamino) benzophenone and dimethylamine (S1 as Supporting Information).9 Analytical Measurements. Differential pulse voltammetry (DPV) was applied as a highly sensitive and rapid electrochemical method for the detection of trace amounts of chlorpheniramine. Figure 5A exhibits DPVs for buffered solutions of chlorpheniramine at pH 2.0 in the concentration range of 1.0 × 10−7 to 1.0 × 10−5 mol L−1 with the detection limit of 8.0 × 10−8 mol L−1. Using the optimum conditions, the linear calibration curves were obtained for chlorpheniramine in the range of 1.0 × 10−7 to 1.0 × 10−5 mol L−1 (Figure 5B). The linear equation is Ip/μA = 86.054 + (6.64C) (R2 = 0.9994, C is in μM).

Ip/μ A = −239.75 + 4061.4ν1/2 /(mV s−1)1/2 R2 = 0.992

(2)

Polarization Studies. The Tafel plot and its corresponding slope were used for elucidation of mechanism of the electrode process. The polarization curves (log I/E plot) for the electrooxidation of chlorpheniramine at the surface of the modified electrode were obtained at various potential sweep rates. The slopes of Tafel plots show αn values between 0.38−0.45 for potential sweep rates in the range of 80−200 mV s−1. By considering α = 0.5, the value of n, was calculated approximately to be 1. So, a mechanism consisting of one electron in the determining step confirmed the electrooxidation of chlorpheniramine at the surface of the modified electrode. To understand the results of the electro-oxidation of chlorpheniramine, a mechanism may be suggested for electrooxidation of chlorpheniramine on the surface of the modified electrode which corresponds to a previous work (Supporting Information, Scheme I).9 As it is reported in literature, taking into account that chlorpheniramine contains an aliphatic 14387

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Table 1. Comparison of Some Electrochemical Methods Which Previously Used for the Determination of Chlorpheniramine LOD (mol/L)

DLR (mol/L)

method

electrode

reference

5.1 × 10−7 1.7 × 10−6 8 × 10−8

7.2 × 10−6−1.8 × 10−5 1.1 × 10−6−1.4 × 10−3 2.0 × 10−6−1.2 × 10−2 1.0 × 10−6−8.0 × 10−4 1.0 × 10−7−1.0 × 10−5

polarography polarography potentiometry voltammetry voltammetry

DME DME CPE-ion exchanger CPE-sodium dodecyl sulfate CPE- Co nanostructure

6 7 8 9 this work

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The repeatability of the modified electrode was investigated in the presence of 1 × 10−6 M chlorpheniramine in buffer solution pH 2.0 and at a potential scan rate of 0.1 V s−1 by using voltammetric measurements for eight measurements. The electrode showed an acceptable repeatability of 93.0%. The relative standard deviation for chlorpheniamine determination, based on the eight replicates of analysis, was 2.74%. The day-today stability of the electrode was monitored for a month. After one month of storage in air, the electrode retained 97.5% of its initial peak current response which shows the long-term stability of the carbon paste modified electrode during the electrochemical determinations in aqueous samples. The detection system is very stable, and the RSD (%) based on six measurements during 1 month, was less than ∼3.2%. Table 1 compares all electrochemical methods which exist in literature. It shows the present research has the best analytical results for the electrochemical determination of chlorpheniramine. For the calculation of the applicability of the proposed route in a real sample analysis, the determination of chlorpheniramine in synthetic serum and commercial tablets was performed. The standard addition method was applied for the calculation of recoveries in the spiking of chlorpheniramine to the synthetic serum. The slope of the calibration curve, which is obtained by the spiked standard solutions was 7.06 μA/μM with a correlation coefficient (R2) of 0.9949. By comparing the two slopes of the standard and spiked drug samples, a recovery of 106.48% was obtained for this method. Chlorpheniamine was determined in a pharmaceutical tablet sample containing 4 mg of chlorpheniamine by using the standard addition method. Seven tablet samples of chlorpheniamine (labeled 4 mg chlorpheniamine per tablet) were powdered, and an aliquot equal to 1 × 10 −5 M of chlorpheniamine was prepared in 0.1 M phosphate buffer with pH 2.0. The slope of the calibration curve, which is obtained by the spiked standard solutions of chlorpheniamine, was 6.72 μA/μM, with a correlation coefficient (R2) of 0.995, and the recovery of 103.40% was calculated.

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ASSOCIATED CONTENT

S Supporting Information *

Electrooxidation mechanism of chlorpheniramine. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: (+)984515514702. Fax: (+)984515514701. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the support of this work by Ardabil Payame Noor University research council, Ardabil, Iran.

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NOMENCLATURE AND ABBREVIATIONS CPE = carbon paste electrode n = number of electrons transferred in the reaction A = surface area of the electrode Do = diffusion coefficient υ = scan rate Co* = concentration Ep = peak potential Ip = peak current F = Faraday constant E0 = formal redox potential R = Gas constant T = temperature LOD = limit of detection DLR = dynamic linear range RSD = relative standard deviation SEM = Scanning electron microscopy DPV = Differential pulse voltammetry CV = Cyclic voltammetry REFERENCES

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CONCLUSIONS

In this research, a carbon paste electrode modified with cobalt nanostructures was demonstrated as a new and effective method for obtaining an efficient sensor for electrochemical measurements of chlorpheniramine. The procedure enables preparation of stable and reproducible electrode. A remarkable improvement in the kinetics of the electron transfer for chlorpheniramine was observed on the surface of the modified electrode. High sensitivity and improved detection limit of the carbon paste modified by cobalt nanostructures are promising for the determination of trace amounts of chlorpheniramine in pharmaceutical and clinical preparations. 14388

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