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A rapid, precise and low cost spectrophotometric method is proposed for the determination of methyldopa and dopamine in pharmaceutical formulations. The crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) was used as an enzymatic source of polyphenol oxidase (PPO; EC.1.14.18.1). This enzyme catalyses the oxidation of catecholamines to the corresponding methyldopaquinone and dopaminequinone...
A flow-injection analysis (FIA) for the determination of dopamine has been developed. The method is based on the inhibition effect of dopamine on the iron(II)-induced chemiluminescence (CL) of 10,10'-dimethyl-9,9'-biacridinium dinitrate (lucigenin). The presence of a non-ionic surfactant, polyoxyethylene (23) lauryl ether (Brij 35), caused an increase in the inhibition effect. The present method allows...
The electrochemistry of dopamine (3-hydroxytyramine) was studied by cyclic voltammetry at a glassy carbon electrode in the presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles at different pH. The anodic peak potential (E pa ) and peak current (I pa ) were found to be remarkably dependent on the charge and the concentration of the surfactant...
A simple method for simultaneous determination of three catecholamines using ion chromatography (IC) with direct conductivity detection (CD) based on the ionization of catecholamines in acidic medium without chemical suppression is developed in the present paper. The method could be used for the determination of these catecholamines in pharmaceutical preparations for the purpose of drug quality control...
Recent research on the pathology and treatment of Parkinson's disease (PD) necessitates the development of methods for analysis of dopamine (DA), an electroactive substance whose content reduces in patients with PD. The concentration variation of dopamine in an experimental Parkinsonian animal model and a treatment model was studied in this paper. For the purpose of detecting dopamine sensitively,...
The property of dopamine in acid-alkaline medium was studied by spectrofluorimetry and spectrophotometry. Effects of organic solvents on dopamine fluorescence spectra were examined and the reason was discussed. Among the organic solvents tested, methanol was selected as sensitizing reagent. A fluorescence quenching reaction took place in basic medium. Mechanism of fluorescence quenching was discussed...
The fabrication and application of an end-column amperometric detection (AD) system with a carbon electrode for capillary-column liquid chromatography (CLC) were described. This new amperometric detector showed good sensitivity and stability in detecting the thiocompounds and other analytes with CLC. In order to obtain the better separation and detection performance for analytes, several operational...
Two maximal potential-resolved flow injection-electrochemiluminescent (FI-ECL) peaks were observed for Ru(bpy) 32+ /TPrA system at 0.90 and 1.05 V, and for Ru(phen) 32+ /TPrA at 1.01 and 1.25 V (vs. Ag/AgCl) in pH 8.0 phosphate buffer solutions. Sensitive ECL inhibition effects were observed in the presence of noradrenaline and dopamine for both of these systems...
Voltammetric behavior of dopamine (DA) on a gold electrode modified with the self-assembled monolayer (SAM) of N-acetylcysteine has been investigated, and one pair of well-defined redox peaks of dopamine is obtained at the SAM modified gold electrode. The oxidation peak current increases linearly with the concentration of dopamine in the range of 1.0x10 -6 to2.0x10 -4 moll...
The electrochemistry of dopamine (DA) was studied by cyclic voltammetry at a glassy carbon electrode modified by a gel containing multi-walled carbon nanotubes (MWNTs) and room-temperature ionic liquid of 1-octyl-3-methylimidazolium hexafluorophosphate (OMIMPF 6 ). The thickness of gel on the surface of the electrode has to be controlled carefully because the charging currents increase with...
A simple and reliable method for simultaneous electrochemical determination of ascorbic acid (AA) and dopamine (DA) is presented in this work. It was based on the use of the cationic surfactant cetylpyridinium chloride (CPC) that enables the separation of the oxidation peaks potential of AA and DA. Cyclic voltammetry (CV) as well as pulse differential voltammetry (PDV) were used in order to verify...
Poly(dimethylsiloxane) (PDMS) microfluidic channels modified by citrate-stabilized gold nanoparticles after coating a layer of linear polyethylenimine (LPEI) were successfully used to separate dopamine and epinephrine, which were difficult to be separated from baseline in native and hybrid PDMS microchannels. In-channel amperometric detection with a single carbon fibre cylindrical electrode was employed...
A sol–gel carbon composite electrode (CCE) has been prepared by mixing a sol–gel precursor (e.g. methyltrimethoxysilane) and carbon powder without adding any electron transfer mediator or specific reagents. It was demonstrated that this sensor can be used for simultaneous determination ascorbic acid, neurotransmitters (dopamine and adrenaline) and uric acid. Direct electrochemical oxidation of ascorbic...
A modified electrode is fabricated by embedding gold nanoparticles into a layer of electroactive polymer, poly(4-aminothiophenol) (PAT) on the surface of glassy carbon (GC) electrode. Cyclic voltammetry (CV) is performed to deposit PAT and concomitantly deposit Au nanoparticles. Field emission transmission electron microscopic image of the modified electrode, PAT-Au nano -ME, indicates the...
Monolayers of 3,3′-dithiodipropionic acid (DTDPA) were prepared on a polycrystalline gold electrode through a self-assembly procedure to produce a gold 3,3′-dithiodipropionic acid self-assembled monolayer (AuDTDPA) modified electrode. The characterization of the AuDTDPA electrode was investigated by cyclic voltammetry and ac impedance using the [Fe(CN) 6 ] 3−/4− redox couple. The electrochemical...
A new rapid, convenient and sensitive electrochemical method based on a gold nanoparticles modified ITO (Au/ITO) electrode is described for the detection of dopamine and serotonin in the presence of a high concentration of ascorbic acid. The electrocatalytic response was evaluated by differential pulse voltammetry (DPV) and the modified electrode exhibited good electrocatalytic properties towards...
Composites of hydroxyl-terminated PAMAM dendrimers, generation 4.0 (64 peripheral OH groups) containing either Ir, Pt or Rh nanoparticles were synthesized and characterized in solution. Each one of these composites was then immobilized on a glassy carbon electrode (GC) and incorporated as an amperometric detector for dopamine in a high-performance liquid chromatograph (HPLC). Comparison of the analytical...
A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently...
A novel biosensor was fabricated by electrochemical deposition of platinum and gold nanoparticles (nanoAu) with l-Cysteine on glassy carbon electrode. It was found that the nanoAu particle size distribution range was (50–80nm), and the platinum particle size range was (200–300nm). The hybrid film could be produced on gold and transparent indium tin oxide electrodes for different kind of studies such...
The present paper demonstrates the preparation and characterization of micro-electrodes based on carbon paste which is composed of carbon nano-particles with an average diameter of 30nm and binding oil. The carbon paste electrode material is encased in pulled glass capillaries ranging in diameter from several tens down to less than ten micro-meters (r=4.5μm). Manipulation of the carbon paste micro-electrode...
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