Chemically Modified Electrodes for the Electrochemical Determination of Selected Pesticides and Pharmaceuticals

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2016-06

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Addis Ababa University

Abstract

In this study, electrochemical sensors were developed for the determination of pesticides and pharmaceutical drugs based on poly(4-amino-3-hydroxynaphthalene sulfonic acid) (poly(AHNSA)), multi-walled carbon nanotubes (MWCNTs), mercury film (MF) and composites of cobalt nanoparticles-polypyrrole (CoNPs/PPy), graphene oxide-polypyrrole (GO/PPy) and multi-walled carbon nanotubes-poly(4-amino-3-hydroxynaphthalene sulfonic acid) (MWCNTs/poly(AHNSA)) modified glassy carbon electrode (GCE). CoNPs/PPy/GCE composite electrode was fabricated by electropolymerization of pyrrole in LiClO4 solution onto the GCE using cyclic voltammetry followed by drop coating CoNPs on the surface of PPy/GCE. The morphological structure and surface analysis of the electrodes were characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy (EDS), Ultra violet-Visible spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The characterization results demonstrated that PPy chains interacted with CoNPs in the composite through donor-acceptor bonds. The sensor exhibited a high electroactive surface area and a low electron transfer resistance towards phoxim. Under the optimal conditions, the sensor showed linear relationship between the peak current and the concentration of phoxim in the range of 0.025 uM12 uM with the detection limit of 0.0045 uM. Besides, the sensor exhibited excellent reproducibility, good stability and selectivity towards possible interfering substances. The sensor was also successfully applied for the determination of phoxim in water samples. Graphene oxide-polypyrrole modified glassy carbon electrode (GO/PPy/GCE) composite was prepared by electrochemical polymerization of a mixture containing 30 uL of GO suspension and 10 uL of 0.25 M pyrrole in 0.1 M LiClO4 using cyclic voltammetry. SEM, FT-IR, UV-Vis and Raman spectroscopy were used to study the morphology and composition of GO/PPy/GCE. The results showed that GO layers have been successfully incorporated into the PPy film. The electrochemical behavior of the sensor was also characterized using EIS and CV. The voltammetric response showed a higher current response and a lower reduction potential at GO/PPy/GCE for phenothrin reduction. The potential shift and current enhancement at the surface of GO/PPy/GCE demonstrated that the sensor exhibited favorable electron transfer kinetics and electrocatalytic activity towards the reduction of phenothrin. The sensor showed a linear response for phenothrin between 0.025 μM to 20 μM and a detection limit of 0.0138 μM. The applicability of the proposed method was carried for the determination of phenothrin in fruit juice samples. Fenitrothion was determined electrochemically on the surface of multiwall carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE). The modified electrode showed three times higher surface active area as compared with glassy carbon electrode. The experimental parameters (amount of MWCNTs, pH of the fenitrothion solution and adsorption parameters) were optimized. The reduction current showed a linear relationship with the concentration of fenitrothion in a range of 0.01 uM to 5.0 uM, with a detection limit of 0.0064 uM. The practical applicability of method was demonstrated in the assessment of fenitrothion in soil and teff samples and good recoveries varied from 86.7% to 93.3% were obtained. The electrochemical behavior of endosulfan was investigated at the surface of glassy carbon electrode modified with mercury film (MF/GCE). The electrode showed a linear response to endosulfan in the concentration range of 0.01-5.0 uM, with a detection limit of 0.0059 uM. The modified electrode also exhibited good stability and reproducibility. The sensor was successfully applied for the determination of endosulfan in onion and tomato samples. A poly(4-amino-3-hydroxynaphthalene sulfonic acid) modified glassy carbon electrode was employed for the simultaneous determination of caffeine and paracetamol using square-wave voltammetry. Poly(AHNSA)/GCE were electrochemically deposited on a glassy carbon electrode by scanning the potential in the potential range of -0.8 V to 2.0 V at a scan rate of 0.1 V s-1 for fifteen cycles in 0.1 M HNO3 solution. The performance of the sensor was investigated using CV and SWV and it showed a linear response for both caffeine and paracetamol in the concentrations range of 10–125 uM. The detection limits were 0.79 uM and 0.45 uM for caffeine and paracetamol, respectively. The effects of some interfering substances in the determination of caffeine and paracetamol were also studied and their interferences were found iii to be negligible which proved the selectivity of the modified electrode. The method was successfully applied for the quantitative determination of caffeine and paracetamol in Coca-Cola, Pepsi-Cola and tea samples. Finally, a sensitive voltammetric method was developed based on glassy carbon electrode modified with a combination functionalized MWCNTs and poly(AHNSA) for the determination of uric acid (UA). The sensor was prepared by drop coating MWCNTs solution on the surface of poly(AHNSA)/GCE. A significant enhancement in the oxidation peak current of UA was observed at MWCNTs/poly(AHNSA)/GCE compared with bare GCE, poly(AHNSA)/GCE and MWCNTs/GCE. The electrode demonstrated a wide linear response in the range from 1.0–100 uM, with a low detection limit of 0.046 uM and was successfully employed for quantification of UA in urine samples

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Chemically Modified Electrodes, for the Electrochemical

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