Electrochemical Detection of Ascorbic Acid Using Pre-treated Graphite Electrode Modified with PAMAM

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Electrochemical Detection of Ascorbic Acid Using Pre-treated Graphite Electrode Modified with PAMAM Dendrimer with Poly (Nile Blue)1 C. Lakshmi Devi1, J. Jayadevi Manoranjitham1, S. Sriman Narayanan1, a 1 – University of Madras, Department of Analytical Chemistry Guindy Campus, Chennai, Tamil Nadu, India a – sriman55@gmail.com DOI 10.2412/mmse.1.74.381 provided by Seo4U.link

Keywords: electro polymerization, pre-treated modified electrode, poly (nile blue), poly (amido amine), ascorbic acid.

ABSTRACT. A new type of PAMAM/PNB modified electrode has been prepared for the electro catalytic oxidation of ascorbic acid. The PAMAM [poly (amido amine)] dendrimer was synthesized based on EDA (ethylenediamine) core in generation (0.5). The graphite electrode is pre-treated by using H2SO4. The PAMAM (G0.5-NH2) dendrimer is polymerized on the pre-treated electrode followed by the electrochemical polymerization of nile blue (NB) over the PAMAM coated electrode. The PAMAM/PNB modified electrode was electrochemically characterized by CV. The cyclic voltammetry behaviour of PAMAM/PNB modified electrode in 0.1M PBS of pH 7 at scan rate of 50mVs -1 showed a pair of redox peaks. The utility of the modified electrode towards the electro catalytic oxidation of ascorbic acid was investigated. It was observed, that the PAMAM/PNB modified electrode showed better electro catalytic oxidation when compared to bare electrode.

Introduction. Ascorbic acid (AA) is a water-soluble antioxidant and called as vitamin C. Since our body is unable to synthesize ascorbic acid by its own metabolism, we take the food with rich sources of AA such as citrus fruits, vegetables, leafy vegetables. The main function of antioxidant is to reduce the oxidative damage caused by the free radicals, which results in improper functioning of cells as excess of free radicals results in oxidative stress [1]. Oxidative stress may causes serious health issues such as damage of normal cells, which leads to cancer, improper protein synthesis, DNA damage etc.

[2]. Insufficient amount of ascorbic acid leads to high blood pressure, stoke cancers, AIDS, atherosclerosis, gallbladder disease etc. [3]. Therefore, it is very important to detect and quantify AA in food sources, pharmaceutical compounds. Various methods have been used for determination of AA among them, electrochemical sensors using conducting polymer dyes have gained much importance and in the bio analytical science because the polymer consists of more number of functional groups which helps in enhancing the sensitivity and electro catalytic activity of sensor device [4]. Some of the early reports where polymer dyes used as sensor for various analyses are poly nile blue [5], [6], poly neutral red [7], poly brilliant crystal blue [8]. PAMAM dendrimers are branched three-dimensional macromolecules with covalent micelles, well-defined cavities, high reactivity and stable compounds used for coating electrodes in order to get physic-chemical properties [9]. Since dendrimer consists of cavities which helps the dye molecules to adsorb in those cavities effectively thereby improving the sensitivity of the modified electrode. Here we report a modified electrode using PAMAM and poly (nile blue) for the determination of AA.

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© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 1. Scheme for fabrication of PGE/PAMAM/PNB electrode.

Experimental Equipment. The electrochemical experiments were carried out using CHI 400A electrochemical system (CH instruments USA). Cyclic Voltammetry (CV) was performed using conventional threeelectrode setup with the PAMAM/PNB modified electrode as the working electrode, a platinum electrode as the counter electrode and standard calomel electrode as the reference electrode. The solutions were made free from oxygen by purging with pure nitrogen. The parameters for the CV were -0.6 to -1.2V. Scan rate 50mV s-1. pH of the solution was measured using digital pH meter (Digisun electronics system). All experiments were performed at ambient temperature.

Chemicals and reagents. Graphite electrode (3mm diameter) was purchased from Aldrich.

Ethylenediamine was purchased from Merck. Ascorbic acid and Nile blue were obtained from Cisco Research Laboratories, India. And all other reagents employed were of analytical grade and used as received. All the supporting electrolytes (0.1 M) and PBS buffer solution (0.1 M) solution were prepared in doubly distilled (DD) water.

Poly (amido amine) dendrimer synthesis. Poly (amido amine) dendrimer was synthesized as reported earlier [10-12]. A round bottom flask (100ml) was taken with the reaction mixture of Ethylenediamine (0.45 g., 7.49 mmol), methanol (MeOH) (10 mL) and methyl acrylate (5.15 g., 59.8 mmol) and the reaction mixture was stirred for 24 hrs. in nitrogen atmosphere at room temperature.

After 24 hrs. reaction mixture was transferred to rotary evaporator to remove the unreacted methyl acrylate, which has resulted in an intermediate product bearing four terminal methyl ester groups (2.98 g., 98.6%). Dissolved 4.93 g. of ethylenediamine in 10 mL methanol was added to the intermediate product and the reaction mixture was stirred at room temperature for 24 hrs. under nitrogen, and then the solvent and excess ethylenediamine were removed using rotary evaporator.

This final product G 0.5 PAMAM dendrimer were synthesized by repeating Michael addition and amidation reaction.

Fabrication of PAMAM/PNB film modified electrode. The base material for preparation of modified electrode is paraffin impregnated graphite electrode (PIGE). The PIGE was prepared as reported earlier [13], [14]. The polished end of the PIGE was dipped into 0.5 M H2SO4 solution and a potential of 1.6 V was applied for 5min to promote the carboxylic acid on the surface of the PIGE electrode. This is called as pre-treated graphite electrode (PGE). The PGE was immersed into 0.1 M NaF solution containing 50µL PAMAM dendrimer. The PAMAM dendrimer was electro deposited to the surface of PGE by applying a potential of 0.6V for 1h. Further, this PGE/PAMAM modified electrode was dipped into the 0.1M PBS (pH 5) containing 0.5 mM nile blue. The nile blue was electro polymerized over the surface of PGE/PAMAM modified electrode by applying a potential of -0.6V to 1.2 V for 20 cycles at a scan rate of 50 mV/s. The resulted PGE/PAMAM-PNB electrode was used for the electro catalytic oxidation of AA. Fig.1 shows the scheme for fabrication of PGE/PAMAMPNB electrode.

Results and discussion Polymerization on nile blue. The electro polymerization of nile blue (NB) over the surface of PGE/PAMAM electrode was carried out by applying potential a potential of ‒0.6V to 1.2 V for 20 cycles Fig.2 shows the cyclic voltammograms of electro polymerization of nile blue over the PEG/PAMAM electrode. The cyclic voltammograms shows two redox couple, the first redox couple MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

around ‒0.4V is due to the oxidation and reduction of the NB monomers. The second redox peak around ‒0.1 V is due to the oxidation and reduction of PNB. The peaks at 0.8 V is due to the monomer.

As the polymerization progresses the peaks at ‒0.1 increases indicated the formation of the PNB. The peak current at ‒0.1V increases for successive cycles due to the growth of the PNB film over the surface of PGE/PAMAM electrode. Once the polymer film is formed, the PGE/PAMAM-PNB electrode was dipped into 0.1M PBS of pH 7 solution and scanned at a potential range from ‒0.6V to 1.2V to conform the formation of polymer film.

Fig. 2. Cyclic voltammograms electropolymerization PNB in 0.1 M PBS (pH 5.3) consists of 0.5 mM NB. Electrochemical determination of ascorbic acid using PAMAM/PNB modified electrode. Under optimized condition such as pH, different electrolyte, and scan rate (figures not shown) the PGE/PAMAM-PNB electrode showed a well defined redox peak in PBS of pH7 at a scan rate of 50mV/s. Thus, PBS of pH7 was used for further studies. In order to investigate the application of PGE/PAMAM-PNB electrode was used for determination AA. Fig. 3 shows the cyclic voltammogram of bare and modified in absence and presence of 1.6×10 -4 M AA. The bare PIGE oxidized AA at 0.3V but the PGE/PAMAM-PNB electrode oxidized at a very lower potential of around 0.2V. Therefore, the PGE/PAMAM-PNB electrode oxidizes AA at very lower potential and the peak current is high when comparing with bare PIGE. This is due to the presence of PAMAM and PNB film, which enhances the electrocatalytic activity of the electrode towards oxidation of AA. Fig.4 shows the cyclic voltammogram response of PGE/PAMAM-PNB electrode on different concentration of AA. On increasing the concentration of AA, the oxidation current is also increased linearly.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 3. CVs of (a) bare, (b) in presence of (1.6X10-4M) Ascorbic acid,(c) PAMAM/PNB film-modified electrode, and (d) in presence of (1.6X10-4M) Ascorbic acid, in 0.1 M PBS (pH7) solution; scan rate: 50 mV/s.

Summary. A highly stable electro active PGE/PAMAM/PNB film modified electrode was fabricated successfully by electro polymerization of NB over PGE/PAMAM electrode. The resulted PGE/PAMAM-PNB electrode was characterized by Cyclic Voltammetry. Further the PGE/PAMAMPNB electrode was used for the electrocatalytic oxidation of AA. The modified electrode was found to be highly stable, selective and sensitive towards the determination of AA. The proposed PGE/PAMAM-PNB film-modified electrode has shown a high determination range is 1.6µM to 1666 µM. Acknowledgements. The authors acknowledge the financial assistance from DST-Inspire fellowship, New Delhi, India, and Department of Science and Technology for PURSE program in support of this work.

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