Analytical & Bioanalytical Electrochemistry
Volume:3 Issue: 5, Oct 2011

The aim of this study was to construct and characterize an ion selective electrode for the potentiometric determination of thorium ions. On hand study we introduced a new calixarene molecule p-tert-butyl-thiacalix[4]arene derivative as ionophore for thorium(IV) selective polymeric membrane electrode. Due to the decisive role of solvent mediators, we fabricated membranes with the plasticizers DBP, DBBP, TEP, OA, DOP, 1-CN respectively and anionic additive NaTPB. The best of the results were obtained with the membrane electrode composition of DBP:PVC:Ionophore:NaTPB (57%:35%:6%:2%). Electrode sensor shows excellent discrimination towards Th4+ ion in presence of other common cations. The resulting data clarified that the electrode shows a Nernstian slope of 14.9±0.6 mV per decade for Th(IV) ions over a broad working concentration range of 8.0×10-8 to 1.0×10-1 mol/L. Our electrode gives the potential response in 7 sec for whole concentration range and this sensor can be used for seven months. Electrode has been successfully applied for many environmental and biological samples of thorium (IV) and as an indicator in potentiometric titration.

The oriented immobilization of antibody is the most critical step in preparation of a highly sensitive immunosensor. In the present report multiwalled carbon nanotubes were treated with nitric acid followed by ethylenediamine to produce amine functionalized carbon nanotubes. To obtain a properly oriented immobilization, initially the sugar chain of antibody (anti-IgG) was oxidized to aldehyde using periodate and then the aldehyde groups were allowed to react with amine groups of carbon nanotubes. The antibody immobilization was verified using the techniques such as field emission scanning electron microscope, Fourier transform infrared, UV-Vis spectroscopy and electrochemistry. Finally determination of antigen (human IgG) was performed in the presence of conjugated horseradish peroxidase as a label, and H2O2 and potassium iodide as the enzyme substrates. At the optimum pH of 7.2, the detection limit of 16.6 ng/ml was obtained for determination of human IgG.

A sensitive and selective electrochemical method for the determination of dopamine (DA) using a crystal violet polymer film modified on carbon paste electrode was developed. The crystal violet polymer film modified electrode poly (crystal violet) MCPE shows excellent electrocatalytic activity towards the oxidation of DA in phosphate buffer solution (pH 7.4). The separation of the oxidation peak potentials for dopamine–ascorbic acid (AA) and dopamine–uric acid (UA) were about 182 mV and 180 mV, respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This modified electrode shows very good selectivity, sensitivity, stability and antifouling property.

The nanostructured conducting polyanilines was synthesized using single and composite structure directing agents such as sodium dodecyl sulphate, sodium dodecyl benzene sulphonate, camphor sulphonic acid by chemical method. The effects of nature and concentration of structure directing agents (both single and composite) on pH characteristics, redox behaviour and solvent pattern were investigated using UV-Vis spectroscopy, Transmission electron microscopy, Cyclic voltammetry and Dynamic light scattering. Both concentration and nature of structure directing agents could influence the pH behaviour and workable pH range. The transition from conducting state to insulating state of all nanostructured conducting polyanilines occurred at higher pH than bulk PANI. The Transmission electron microscopy and Dynamic light scattering results showed that the morphology and the dimension of nanostructured conducting polyanilines at the doped and undoped state depended on the nature of structure directing agents used for polymerization. The redox properties were independent of nature and concentration of structure directing agents but electrochemical activity and solution behaviour of nanostructured conducting polyanilines depended on the nature of structure directing agents.

Density functional theory method at the level of B3LYP/6-31G(d,p) in combination with the polarizeable continuum model have been used to compute one-electron oxidation potentials for eighteen N-hydroxy compounds in aqueous solution. Analysis of correlation between the experimental oxidation potentials and the theoretically calculated values revealed that notable relations existed between the experimental potentials and the eigenvalues of SOMO's of the N-Hydroxy {-N (OH)-} derivatives.

A mathematical model of enzyme flow calorimetry for the monitoring of hysteresis behaviour of immobilized enzyme is developed. The model is based on diffusion equations containing a non linear term related to substrate inhibition kinetics of the enzymatic reaction. This paper presents an approximate analytical method (He’s Homotopy perturbation method) to solve the non-linear differential equations for spherical, cylindrical and planar particles. Closed and simple analytical expressions for substrate concentration have been derived for all possible values of parameters. These results are compared with numerical results and are found to be in good agreement. The obtained results are valid for the whole solution domain.

An experimental investigations concerning the preparation and characterization of the superionic composite system [CdHgI4:xAgI], (x=0.2, 0.4, and 0.6 mol. wt. %), have been undertaken with a view to evaluate the ionic transport properties of the mixed composite system, and to identify the phase transition. Powder samples of various compositions containing x mol. wt. %AgI were synthesized by solid state reactions, where[CdHgI4] system was used as host. Samples were analyzed using powder X-ray diffraction,thermal gravimetric analysis (TGA) techniques. These studies have revealed the formationof new substance having phase transition temperature similar to that of AgI. Detailed electrical conductivity measurement carried out at frequencies of 100 Hz, 120 Hz, 1 kHz,and 10 kHz in the temperature range 150-250 °C by a Gen Rad 1659 RLC Digibridge, haveidentified the best conducting composition namely 4 mol. wt. %, exhibiting an electricalconductivity of 1.88×10-1 Scm-2K at 543 K and an activation energy of 1.66 eV for Ag+ ion migration within the solid host. Activation energies for the system in eV both for the pretransition and post-transition phase transformations are reported.

This work introduces a PVC membrane sensor for determination of clidinium active ingredient. For the membrane preparation, clidinium-tetraphenyl borate ion-pair was employed as a sensing material in the PVC membrane. Several plasticizers were studied in the membrane composition dibutyl phthalate (DBP), benzylacetat (BA), and nitrobenzene (NB). After a series of experiments, the best electrode response was obtained from a membrane composed of NB. The electrodes illustrated a fast, stable and Nernstian response over a wide clidinium bromide concentration range of 1×10-5 to 1×10-1 M, in the pH range of 4.0–10.0.