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Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com Multi-walled carbon nanotube (MWCNT)-chitosan (CHIT) chemically modified glassy carbon electrode (GCE), designated as GCE/MWCNT-CHIT has been developed by modifying a suspension of MWCNT + CHIT-acetic acid mixture on a cleaned GCE and demonstrated as a selective electrochemical detector (ECD) for flow-injection analysis (FIA) of hydrogen peroxide. The GCE/MWCNT-CHIT showed stable surface confined redox feature at E0´= –0.22 V vs Ag/ AgCl with surface excess value 13.63 nmol cm–2 in pH 7 PBS. Under an optimal condition, applied potential = –0.2 V vs Ag/AgCl, hydrodynamic flow rate = 0.75 mL min–1 and pH 7 phosphate buffer as a carrier solution, the FIA-ECD showed H2O2 calibration plot in an range 50–2500 µM with detection limit and current sensitivity values 9.7 µM and 0.59 nA µM–1 (0.8345 A M–1 cm–2) respectively. There was no interference from cysteine, ascorbic acid, uric acid, nitrite, and nitrate. A cosmetic cream, clinical H2O2 and milk were further tested as real samples with ~100% recovery values.

Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com Selective electrochemical detection of ascorbic acid (AA) in fruit juice is an important analytical problem. Since electrochemical techniques offer an easy extension to portable device, design and development of new chemically modified electrodes, which can able to sense AA is most wanted in quick quality control assessment. Herein we report, an electro-copolymerized aniline/N-(1-naphthyl)ethylene-diamine (NED) on MWCNT modified gold electrode (Au/ MWCNT@PANI-NED) in a neutral pH solution for highly efficient and low potential detection of AA in canned fruit juice. The NED acts as a linker to improve the stability of the polyaniline/MWCNT composite in neutral pH. The electrochemical sensor showed AA oxidation peak at low potential, –15 mV vs Ag/AgCl in pH 7 phosphate buffer solution. The Au/MWCNT@PANI-NED was characterized by cyclic voltammetry, Raman, FT-IR and UV-Vis spectroscopy techniques. Under optimal amperometric i–t condition, Au/MWCNT@PANI-NED showed AA calibration plot in a window 200–2000 µM with a current sensitivity of 13.45 nA µM–1. A canned fruit juice real sample was successfully analyzed with recovery value ~100%.

Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com Ethoxyquin (EQ) is a common preservative used in several animal feeds such as fish, poultry and dairy food products. Excess addition of the EQ, (>75 ppm) to food products led to several health problems. Different analytical methods have been proposed for the determination of EQ in food samples. Unfortunately, existing methods are complicated and expensive. Here in, we report a selective and non enzymatic electro-analytical assay based on a multi-walled carbon nanotube modified glassy carbon electrode (GCE/MWCNT) with pH 7 of 0.1 M phosphate buffer solution for EQ analysis. A dilute ethanolic solution of EQ adsorbed GCE/MWCNT, i.e. GCE/MWCNT@EQ showed well-defined surface confined redox peak at –0.2 V vs Ag/AgCl, which is due to formation of a quinoline derivative on the interface. The peak potential and current values were taken as specific tool for the EQ quantification assays. Repeated experiment on unmodified GCE failed to show any such defined redox peak. The developed chemically modified electrode (CME) was characterized by Raman spectroscopy and FT-IR.

Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com A methyl orange (MO) dye electrochemically immobilized multi-walled carbon nanotubes modified glassy carbon electrode, designated as GCE/MWCNT@MO, has been prepared and used for selective determination of ascorbic acid (AA, vitamin C) at a very low potential (–140 mV vs Ag/AgCl) by voltammetric techniques in pH 7 phosphate buffer solution. Physicochemical characterization of the modified electrode by FTIR and Raman revealed presence of surface confined MO on MWCNT matrices. Electrochemical investigations like loading, scan rate, pH and concentration effects were studied. Amperometric i–t response showed a AA linear calibration range 25–600 µM with a correlation coefficient of 0.9985 and detection limit 150 nM. The present system doesn’t show any interference with nitrite, cysteine, glucose and dopamine. Some pharmaceutical formulations were tested with the present system with appreciable recovery values.

Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com An electrochemical sensor based on graphitized carbon nanofibers modified on glassy carbon electrode (GCE/ CNF) has been developed for simultaneous determination of guanine and adenine in pH 7 phosphate buffer solution (PBS). In cyclic voltammetry (CV), GCE/CNF shows two well-defined and well-separated irreversible oxidation peaks at 0.74 and 0.98 V vs Ag/AgCl for electrochemical oxidations of guanine and adenine, respectively when compared to unmodified GCE. Whereas, unmodified GCE shows feeble peak response for guanine and adenine in physiological medium. Differential pulse voltammetric (DPV) technique was further used for the quantification assays. As like CV, DPV also showed well-defined and well-separated current signals for guanine and adenine at 0.66 and 0.92 V vs Ag/AgCl, respectively. Note that CNF is about ten times lesser cost than multi-walled carbon nanotubes. DPV technique was further adopted for simultaneous determination of guanine and adenine. DPV parameters are systematically optimized in pH 7 PBS in the presence of mixture of analytes using the modified electrode. GCE/CNF shows good stability with linear range of 15–105 µM and 15–120 µM for guanine and adenine detections, respectively. Obtained sensitivity and detection limits (S/N=3) are comparable and superior than previously reported carbon based modified electrodes.

Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com Chemically modified electrodes (CMEs) are the recent impeccable achievements of electrochemists. The point lies in making simpler CMEs without any complicated methods of preparations. Here in, we present a graphite nanopowder (GNP) coated glassy carbon electrode (GCE), designated as GCE/GNP, for simple electrochemical sensing of H2O2 in pH 7 phosphate buffer solution. Note that H2O2 is extensively used in cosmetics and food products (as preservative in milk) and if the usable concentration exceeds certain limit then it may lead to severe health hazards. Thus, simple and low cost detection methodologies are most needed for the real sample analysis. Meanwhile, carbon nanomaterial have attracted great interest among researchers due to their unique structures, good electrical, mechanical, and chemical properties. GNP is one of such carbon nanomaterial which is very cheap and easy available in market. Here in we report a GCE/GNP modified electrode, without any enzyme and addition redox mediator, as a sensor for H2O2 . CV of the GCE/GNP showed a H2O2 -reduction peak at –0.5 V vs Ag/AgCl in pH 7 phosphate buffer solution. Control experiments with activated charcoal modified and unmodified glassy carbon electrodes failed to show any such marked H2O2 reduction signal. Furthermore, GCE/GNP was subjected to amperometric i–t curve technique which gave significant response to H2O2 -sensing. Biochemicals like cysteine, ascorbic acid, uric acid, dopamine and nitrate were also tested for interference.

Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com Hydrazine and its derivatives are toxic and can cause several health hazards including cancer. It is highly challenging to develop a selective sensing technique for hydrazine in real samples. In this work, a new electrochemical sensor for hydrazine based on a nickel hexacyanoferrate chemically modified disposable gold barrel plated electrode (AuBPE/NiCHF) has been developed. AuBPE/NiHCF showed stable and well defined surface confined redox peak at 356 mV vs Ag/AgCl in pH 7 Na2 SO4-NaOAc. Under an optimal cyclic voltammetric condition, the modified electrode showed a linear current response for hydrazine concentration in a range 0.5–10 mM with current sensitivity value of 35.32 µA/mM. Amperometric i–t method of hydrazine detection yielded current sensitivity and detection limit values 0.2052 µA/µM and 51 nM respectively. The AuBPE/NiHCF is tolerable to co-existing interferences such as oxalic acid, citric acid, nitrite, dopamine and uric acid. Three different water samples were successfully analyzed for the hydrazine detection with appreciable recovery values.