1Introduction dation potential was higher,i na greementw ith TP structure. Formalp otentials in aqueous solutions that have been previouslyu navailable from electrochemistry of CA and TP were thus obtained. In the determinations of CA and TP,s ensitivity and linear dynamic range (LDR)i n FSV were 1.84 mA cm À2 mM À1 and 0.20-22.0 mmol L À1 and 1.46 mA cm À2 mM À1 and 0.50-30.0 mmol L À1 ,r espectively. FSV determination of CA in coffee sample is demonstrated and the results are in agreement with the results obtained by HPLC-UV.
A novel electrochemical sensor was constructed for the impedimetric and voltammetric determination of gemfibrozil (GEM) by modification of the glassy carbon electrode (GCE) using multi-walled carbon nanotubes (MWCNTs) and gold nanoparticles (Au-NPs). The inherent properties of MWCNTs such as their high surface area and high conductivity, and the capability of fast electron transfer of Au-NPs were taken into account in constructing the sensor. Scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and electrochemical impedance spectroscopy (EIS) were used for the characterization of the MWCNTs/Au-NPs modified GCE (GCE/MWCNT/Au-NP) surface. The redox behavior of GEM on the surface of GCE/MWCNT/Au-NP was studied by voltammetric techniques. After optimizing the effective experimental parameters, the sensor's response toward increasing GEM concentration was studied by square wave voltammetry (SWV) and EIS. The results obtained showed linear responses in the GEM concentration ranges of 0.15-45.0 and 0.10-45.0 μmol L −1 for SWV and EIS, respectively. The experimental 3σ detection limits were 0.10 and 0.074 μmol L −1 for SWV and EIS, respectively. The repeatability of 1.07% and reproducibility of 5% were achieved for five replicate determinations of 15.0 μmol L −1 of GEM. The sensor efficiency was investigated by its application in the analysis of the real samples pharmaceutical and spiked human serum, and the results obtained were satisfactory.
[a] 1Introduction Dopamine (DA) is ac atecholamine derivative,a nd, as an eurotransmitter, plays am ajor rolei na ddiction [ 1]. Dopamine affects the brain processes that control movement, emotional response,a nd the ability to experience pleasure and pain. Regulation of DA plays ac ritical role in our psychological and physical health [2].S erious diseases such as Schizophrenia and Parkinsonism may result from the losso fD A-containing neurons [3][4][5].T herefore, the development of simple and selective methods is of interest for the detection and determination of DA by the neuroscientists and chemists.T he use of severalm ethods such as flow injection [6,7],high performance liquidchromatography (HPLC) [8,9],g as chromatography [10],a nd spectrophotometry [11] have been reported for the determination of DA in different samples.A lthough these methods may provideh igh selectivity,t hey also bring some disadvantages such as the operation complexity, time consumption, and use of high-cost instruments. Amongt he differenta nalyticalm ethods,t he electrochemical determination method has demonstrated to be highly sensitive and reliable,w ith less interference from the non-electroactive substancesf or the determination of several electroactive components [12][13][14].R ecently,d evelopment of voltammetric sensors based upon the chemically modified electrodes (CMEs) has receivedc onsiderable interest in the DA detection and determination. Up to the presentt ime,d ifferentC MEss uch as the polymerized electrodes [15][16][17],c arbon ionic liquid electrodes [18][19][20], nano-material-modified electrodes [21][22][23],a nd self-assembled monolayers [24][25][26] have been used in the voltammetric sensingo fD A. Them ain intrinsic disadvantages of such CMEs are their poor stability,n on-uniform thickness of the adsorbed films,a nd poor reproducibility of the electrodes.F urthermore,t he electrode surface cannot be renewed, and thust he irreversible adsorption of contaminationa nd the memory effect have destructive effects on the routine determination of DA.Anew reproducible surface,a bility to control the amounto fm odifier, al ow residual current, and ap orous surface could be obtained by modificationo ft he carbon paste electrodes (CPEs). Chemical modification of CPEs is carriedo ut simply by bulk modification, in which, the modifieri si ncorporated into the CPE matrix [27][28][29].T herefore,t he chemically modified carbon paste electrodes (CMCPEs) have extensive analyticala pplications [30,31].B esides, different types of CMCPEs have been used for the electro-chemical determination of DA [28,[32][33][34][35][36][37][38][39][40][41][42][43].1,4-Michael addition reactioni sawell-known protocol, which has been widely appliedtothe electrochemical synthesis of different organic compounds [44][45][46].I nt his procedure,t he oxidation of catechol derivatives (as substrate) yields the corresponding o-benzoquinones,s ince the electro-generated o-benzoquinonesa re active intermediates,a nd readily undergoM ichael addition re...
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