Analytical & Bioanalytical Electrochemistry
Volume:8 Issue: 3, Feb 2016

In this paper, we report a new measurement technique for tea polyphenols by linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The enzyme tyrosinase was also extracted from crude cheap sources such as potato. Platinum working electrode was modified with this enzyme and electrochemical techniques were performed on the enzyme-modified electrode to exploit the oxidation of polyphenols. Various grades of tea were tested for total polyphenols (TP) by linear sweep voltammetry and impedometry and the results were compared with those obtained by HPLC. A very good correlation index of 0.97 was obtained between the TP content by HPLC and LSV and that obtained between the TP content by HPLC and impedometric analysis was 0.95 for purified tyrosinase from potato. The methods exhibited very low limits of detection (0.54 mg/L) and the measurement time was also quite fast (300 seconds). The results ensured LSV and impedometric analysis to be useful techniques for determination of TP in tea and hence gradation of tea in a very simple but effective way.

This paper has presented a novel strategy to carry out the direct and sensitive determination of nitrite ion in different and complex matrices based on a new nano-composite carbon paste electrode composed of (Au-Pd@MWCNT/Gr)-CPE. The characteristics of the proposed nano-materials were investigated by scanning electron microscopy and X-ray diffraction. The effects of various experimental parameters on the electrochemical response of the nitrite ions were assayed and optimized. Under the optimized conditions, the calibration curve for nitrite ion concentration was linear in the range of 0.02-55.0 µmol L-1 with the detection limit of 9.44 nmol L-1. In addition, the suggested sensor was successfully applied to the determination of nitrite ion in sausages, cheese, plant foodstuffs, soil, mineral water and tap water samples with satisfactory results. However, the prepared sensor may hold great promise for fast, simple and sensitive detection of nitrite in various real samples.

A simple and rapid voltammetric oxidation of methocarbamol was investigated. In pH 3.0 phosphate buffer, methocarbamol shows an irreversible oxidation peak at about 1.28 V at a multi-walled carbon nanotube (MWCNT)-modified glassy carbon electrode. The cyclic voltammetric results indicate that MWCNT-modified glassy carbon electrode showed that methocarbamol at 12 µL of MWCNT, the oxidation sites of glassy carbon was adsorbed by MWCNT which increased only the current sensitivity. Under optimized conditions, the concentration range and detection limit are 6.0×10-6 to 1.0×10-4 M and 4.22×10-6 M, respectively for methocarbamol. The proposed method was successfully applied to methocarbamol determination in pharmaceutical samples. The analytical performance of this sensor has been evaluated for the detection of analyte in urine sample.

An ionic liquid– magnetic core–shell Fe3O4@SiO2/graphene nanocomposite modified carbon paste electrode (ILFSGCPE) was used as a fast and sensitive tool for the investigation of the electrochemical oxidation of ascorbic acid using voltammetry. This modified electrode has been fabricated using hydrophilic ionic liquid (n-hexyl-3methylimidazolium hexafluoro phosphate) as a binder. The modified electrode offers a considerable improvement in voltammetric sensitivity toward ascorbic acid, compared to the bare electrode. Using differential pulse voltammetry (DPV), the electrocatalytic oxidation peak current of ascorbic acid shows a linear calibration curve in the range of 1.0×10-6 to 9.0×10−4 M ascorbic acid. The limit of detection was equal to 2.3×10-7 M. The electrode was also employed to study the electrochemical oxidation of ascorbic acid in the presence of Lcysteine.

An electrochemical sensor for sensitive determination of isoniazid (INH) using multi-walled carbon nanotubes-cetyltrimethyl ammonium bromide (CTAB) surfactant composite on the surface of a glassy carbon electrode was developed. The peak current increased greatly compared with bare GCE and MWCNT/GCE electrode. The oxidation process was irreversible over pH range studied and exhibited a diffusion controlled behavior. The current response was found to be directly proportional to the concentration of INH in the concentration range of 1.0×10-7 M to 1.2×10-6 M with a limit of detection (LOD) of 2.14×10-9 M. The modified electrode showed good selectivity and reproducibility. The developed analytical method was successfully applied to isoniazid determination in human serum and urine samples. This method can be employed in clinical analysis, quality control and routine determination of drugs in pharmaceutical formulation.

A carbon paste electrode was modified with anionic surfactant sodium dodecyl sulphate (SDS) solution by immobilization method; surfactant solution was strongly adsorbed on the carbon paste electrode (CPE) and applied to the simultaneous detection of norepinephrine (NE) in the presence of ascorbic acid (AA) and folic acid (FA). The electrochemical response of the SDS modified CPE (SDS/CPE) was evaluated with respect to pH, preconcentration time, scan rate and other variables by cyclic voltammetric technique. The concentration variation of SDS (modifier) results in optimization of the modified electrode and also the good electrocatalytic performance of the SDS/CPE were tested on the redox behavior of the potassium ferricyanide. The present method provided a simple method for the detection of NE in biological samples. Electron transfer of NE redox at bare carbon paste electrode was too slow as compared at SDS/CPE. The SDS/CPE showed reversible electrochemical behavior of NE with a formal potential of 0.065 V versus SCE. The interfacial process between the SDS/CPE and NE in 0.2 M PBS (pH 7.0) was investigated with their electrochemical reaction and the results indicated that the two electron two proton transfer was involved in the electrode reaction process. Under optimal conditions a detection limit of 1 µM was obtained.

The possibility of pyriproxyfen electrochemical detection in water (in neutral, or alkaline pH conditions) has been studied. During the analysis, piriproxyfen is transformed in a yet studied quinone-hydroquinonic system before the electrochemical reaction. By means of mathematical model development and analysis, using the linear stability theory and bifurcation analysis, the analytical efficiency conditions have been detected, including the optimal pH and potential range. The oscillatory and monotonic instability conditions have also been detected. These instabilities may be caused by double electric layer influences of the electrochemical reaction. The analysis may be driven in the presence of different organic, hybrid and inorganic modifiers. Nevertheless, the specific conditions for electrode modifying material stability are required for the electrochemical analysis of piriproxyfen.

In this work, a new method was proposed for the evaluation of recognition capability of the ion imprinted polymers based on competitive displacement coupled with indirect electrochemical detection technique. Nano-sized Eu3+imprinted polymer was synthesized using ultrasonic assisted suspension polymerization in silicon oil. Differential pulse voltammetry technique and carbon paste electrode, modified with the synthesized ion imprinted polymer (IIP), were applied for the evaluation of the rebinding characteristics of the IIP. A competitive substitution method was applied for the evaluation of recognition property of the IIP towards lanthanides and some other ions which were non-electroactive in traditional conditions. For this aim, Pb2 ions, included in the selective cavity of the Eu3+IIP, were replaced with Eu3 ions, reducing the differential pulse voltammetry signal of Pb2. Different factors such as extraction pH, IIP amount in the carbon paste electrode and competitive extraction time were evaluated and optimized. By the proposed method the recognition ratios and selectivity coefficients of the synthesized IIP for different lanthanides and some other ions were obtained.

Me2-dibenzo[b,k]-dipyridyl[f,o][1,4,7,10,13,16]-hexaaza-5,9,14,19-tetraoxocyclooctadecane macrocyclic complexes of Fe(III) and Ni(II) have been synthesized by template method and analysed with various techniques like molar conductance, FT-IR, UVVis, Mass spectra. The studies of surface-modified electrode based on tThe oxidative electropolymerisation of the monomeric Fe[Me2-(DBDPy)N6tetraoxo[18]Cl2]Cl and Ni[Me2(DBDPy)N6tetraoxo[18]Cl2] complexes were carried out on the Pt electrode in DMSO containing 0.1 M TEAP, by employing cyclic voltammetry. A thin film of polymer, [M-Me2(DBDPy)N6tetraoxo[18]Cl2]n , where M=Fe(III) and Ni(II), was formed on the electrode surface by constant potential electrolysis at 1.5 V on cycling from -1.5 to .0 V vs Ag/AgCl.The monomers, after polymerization form [M-Me2-(DBDPy)N6tetraoxo[18]Cl2]n , where M=Fe(III) and Ni(II), which form a thin film on the electrode surface. The film formed on the electrode surface by constant potential electrolysis at 1.5 V on cycling from -1.5 to .0 V vs Ag/AgCl The magnitude of film growth depends on the method of deposition in the solvent and the rate of cycling i.e 10 cycles from -1.5 to .0 V vs Ag/AgCl at 200 mVs-1 scan rate resulted in “Polymer layers” formation on Pt electrode. Film growth was also dependent on the concentration of the electrolyte and the electrode surface and found that the heterogeneous electron transfer rate constant is increased with the growth of the film. UVVisible and FT-IR spectra suggest that the macrocycles remained in the polymeric film.

Vitamin B1, also known as thiamine or thiamin or «thio-vitamine» is used by all living organisms. The compound is synthesized by bacteria, fungi, and plants, and hence animals have to obtain it from external sources. Vitamin B1 is an essential nutrient for human beings too. The present work focuses on the development of symmetric and asymmetric PVC membrane sensors for the selective determination of Thiamine. The membranes were prepared through the incorporation of thiamine-tetraphenyl borate ion-pairs, as the ionophore, in PVC membranes, based on different plasticizers (i. e. dibutyl phthalate (DBP), benzyl acetate (BA) and nitrobenzene (NB) ). Based on the results of the optimization experiments, the best sensor performance was found in the case of DBP-based membranes. The optimal symmetric electrodes were found to produce fast and stable Nernstian responses from in thiamine solution in the concentration window of 5. 0×10-6-1. 0×10-1 mol L-1, while the asymmetric sensors (the graphite coated electrodes) led to linear responses in the range of 5. 0×10-7 – 1. 0×10-2 mol L-1. The electrodes revealed pH independent responses in the pH range of 2. 0-5. 0. The validation of the methods, based on the application of the developed sensors, revealed the devices to be suitable for application in the analysis of the target species in pharmaceutical formulations.