Preparation, Characterization and Application of Chemically Modified Glassy Carbon Electrodes for Square Wave Voltammetric Determination of Selected Pharmaceutical Drugs

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2018-05-03

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Addis Ababa University

Abstract

In this thesis, various types of simple, scalable and low cost chemically modified electrodes were successfully developed for the sensitive and selective determination of some commonly and widely used pharmaceutical drugs. First, a simple and fast modification of conventional bare glassy carbon electrode (GCE) with poly(L-aspartic acid) was performed by electropolymerization of L-aspartic acid (L-Asp) using cyclic voltammetry for the determination of ibuprofen (IBP). The poly(L-Asp)/GCE was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and electroactive surface area (ESA) measurements. The cyclic voltammetric and square wave voltammetric study of IBP in 0.25 M acetate buffer solution (ABS) at pH 4 showed an obvious electrocatalytic effect towards IBP oxidation, which resulted in a higher current response and a negative shift in the peak potential at the polymer film modified electrode compared to the bare GCE. Under the optimized conditions, a linear calibration curve was obtained using square wave voltammetry (SWV) at the poly(LAsp)/ GCE in the range of 1 to 150 μM with a limit of detection (LOD, 3Sb/m) and a limit of quantification (LOQ, 10Sb/m) of 0.22 and 0.74 μM, respectively. Next, a poly(L-aspartic acid)/functionalized multi-walled carbon nanotubes composite modified glassy carbon electrode, P(L-Asp)/f-MWCNTs/GCE, was prepared for the simultaneous determination of caffeine (CF) and theophylline (TP) using SWV. The electrode preserves and combines the properties of the individual modifiers synergistically. A significant enhancement in the peak current response of CF and TP were observed accompanied with a negative shift in peak potentials at the composite modified electrode compared to the bare electrode. The prepared electrode exhibited excellent SWV responses towards the simultaneous determination of CF and TP in the range of 1‒150 and 0.1‒50 μM with a limit of detection of 0.28 and 0.02 μM, respectively. Similarly, a sensitive poly(L-aspartic acid)/electrochemically reduced graphene oxide modified GCE, P(LAsp)/ ERGO/GCE, was developed for epinephrine (EP) determination by electrochemical reduction of GO drop coated on GCE in 2 mM L-aspartic acid by CV in pH 6 phosphate buffer solution (PBS) which gives rise to in situ polymerization of L-aspartic acid on the electrochemically reduced graphene oxide. Raman, FTIR and UV spectroscopies were used to characterize GO, ERGO, P(L-Asp) and P(L-Asp)/ERGO composite. The electrochemical response of P(L-Asp)/ERGO/GCE towards EP determination was characterized by EIS, CV and ii ESA measurements. The CV results showed a significant enhancement in the peak current response accompanied with a negative shift in the peak potential for EP at the composite modified electrode. The prepared P(L-Asp)/ERGO/GCE exhibited excellent SWV response towards EP determination in the range of 0.1‒110 μM with LOD and LOQ of 0.025 and 0.083 μM, respectively. The method was further validated by UV assay and the obtained results confirmed the applicability of the developed method for routine analysis. Lastly, a new GCE modified with electrochemically reduced graphene oxide decorated with nickel nanoparticles (NiNPs/ERGO/GCE) was developed by electrodeposition. TEM, SEM, EDS, SAED, EIS, CV and SWV were used for the characterization of the synthesized GO, NiNPs and the prepared novel platform, NiNPs/ERGO/GCE. The as prepared platform was used for the determination of diclofenac (DIC) and ethambutol (ETB). A significant enhancement in the peak current response for DIC and ETB was observed at the composite modified electrode compared to the unmodified electrode. The composite modified electrode demonstrated excellent SWV response towards the determination of both DIC and ETB in the working range of 0.25‒125 μM and 0.05‒100 μM with LOD of 0.09 and 0.023, respectively. Generally, all the developed sensors were validated successfully for real sample analysis in pharmaceutical formulation and human urine samples with good recovery results. The proposed sensors also displayed good repeatability, reproducibility, long-term stability and selectivity towards potential interferents and are promising materials for electrochemical sensing of similar drugs and biologically active compounds in real samples.

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Electroanalytical Methods, Methodology and Techniques Used in the Study, Electrochemical Sensors

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