Preparation Characterization And Application Of Chemically Modified Glassy Carbon Electrodes For Square Wave Voltammetric Determination Of Selected Pharmaceutical Drugs

In this thesis, various types of simple, scalable and low cost chemically modified electrodes werernsuccessfully developed for the sensitive and selective determination of some commonly andrnwidely used pharmaceutical drugs. First, a simple and fast modification of conventional barernglassy carbon electrode (GCE) with poly(L-aspartic acid) was performed byrnelectropolymerization of L-aspartic acid (L-Asp) using cyclic voltammetry for the determinationrnof ibuprofen (IBP). The poly(L-Asp)/GCE was characterized by cyclic voltammetry (CV),rnelectrochemical impedance spectroscopy (EIS) and electroactive surface area (ESA)rnmeasurements. The cyclic voltammetric and square wave voltammetric study of IBP in 0.25 Mrnacetate buffer solution (ABS) at pH 4 showed an obvious electrocatalytic effect towards IBPrnoxidation, which resulted in a higher current response and a negative shift in the peak potential atrnthe polymer film modified electrode compared to the bare GCE. Under the optimized conditions,rna linear calibration curve was obtained using square wave voltammetry (SWV) at the poly(LAsp)/rnGCE in the range of 1 to 150 μM with a limit of detection (LOD, 3Sb/m) and a limit ofrnquantification (LOQ, 10Sb/m) of 0.22 and 0.74 μM, respectively. Next, a poly(L-asparticrnacid)/functionalized multi-walled carbon nanotubes composite modified glassy carbon electrode,rnP(L-Asp)/f-MWCNTs/GCE, was prepared for the simultaneous determination of caffeine (CF)rnand theophylline (TP) using SWV. The electrode preserves and combines the properties of thernindividual modifiers synergistically. A significant enhancement in the peak current response ofrnCF and TP were observed accompanied with a negative shift in peak potentials at the compositernmodified electrode compared to the bare electrode. The prepared electrode exhibited excellentrnSWV responses towards the simultaneous determination of CF and TP in the range of 1‒150 andrn0.1‒50 μM with a limit of detection of 0.28 and 0.02 μM, respectively. Similarly, a sensitivernpoly(L-aspartic acid)/electrochemically reduced graphene oxide modified GCE, P(LAsp)/rnERGO/GCE, was developed for epinephrine (EP) determination by electrochemicalrnreduction of GO drop coated on GCE in 2 mM L-aspartic acid by CV in pH 6 phosphate bufferrnsolution (PBS) which gives rise to in situ polymerization of L-aspartic acid on thernelectrochemically reduced graphene oxide. Raman, FTIR and UV spectroscopies were used torncharacterize GO, ERGO, P(L-Asp) and P(L-Asp)/ERGO composite. The electrochemicalrnresponse of P(L-Asp)/ERGO/GCE towards EP determination was characterized by EIS, CV andrniirnESA measurements. The CV results showed a significant enhancement in the peak currentrnresponse accompanied with a negative shift in the peak potential for EP at the compositernmodified electrode. The prepared P(L-Asp)/ERGO/GCE exhibited excellent SWV responserntowards EP determination in the range of 0.1‒110 μM with LOD and LOQ of 0.025 and 0.083rnμM, respectively. The method was further validated by UV assay and the obtained resultsrnconfirmed the applicability of the developed method for routine analysis. Lastly, a new GCErnmodified with electrochemically reduced graphene oxide decorated with nickel nanoparticlesrn(NiNPs/ERGO/GCE) was developed by electrodeposition. TEM, SEM, EDS, SAED, EIS, CVrnand SWV were used for the characterization of the synthesized GO, NiNPs and the preparedrnnovel platform, NiNPs/ERGO/GCE. The as prepared platform was used for the determination ofrndiclofenac (DIC) and ethambutol (ETB). A significant enhancement in the peak current responsernfor DIC and ETB was observed at the composite modified electrode compared to the unmodifiedrnelectrode. The composite modified electrode demonstrated excellent SWV response towards therndetermination of both DIC and ETB in the working range of 0.25‒125 μM and 0.05‒100 μMrnwith LOD of 0.09 and 0.023, respectively. Generally, all the developed sensors were validatedrnsuccessfully for real sample analysis in pharmaceutical formulation and human urine samplesrnwith good recovery results. The proposed sensors also displayed good repeatability,rnreproducibility, long-term stability and selectivity towards potential interferents and arernpromising materials for electrochemical sensing of similar drugs and biologically activerncompounds in real samples.

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