Analytical & Bioanalytical Electrochemistry
Volume:7 Issue: 2, Apr 2015

A novel molecularly imprinted polymer (MIP) electrochemical sensor for selective detection of cholesterol has been developed by grafting a very thin polymer film on the surface of the functionalized-carbon nanotube (f-CNT) modified gold electrode. This sensor was made by electropolymerization of 2-mercaptobenzimidazole in the presence of cholesterol as a template on the surface of carbon nanotube modified gold electrode. Since cholesterol did not have any electroactivity on MIP/MWCNT/Au electrode in the phosphate buffer; indirect method was used for the determination of cholesterol. In this method, K3Fe(CN)6/K4Fe(CN)6 redox couples was used as an electrochemical probe to characterize the sensor using cyclic voltammetry, differential pulse voltammetry and chronoamperometry methods. The linear response range for cholesterol detection was between 2 and 350 mg.dL-1 with a detection limit of 1 mg.dL-1. The sensor exhibited good selectivity for cholesterol, with a satisfactory reproducibility and repeatability. The proposed electrode was successfully applied for determination of cholesterol in human blood serum.

Poly-(threonine) film modified carbon paste electrode was successfully fabricated through electropolymerization technique and was applied to investigate the electrochemical behaviors of hypoxanthine (HX) and xanthine (Xa) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The oxidation peak currents for HX and Xa were strong, well resolved, and linear over the range of 8×10-6 M to 1×10-3 M. The limits of detection for HX and Xa by DPV were found to be 0.10mM and 0.08mM, respectively.

Orphendrine hydrochloride an anticholinergic drug was electrochemically studied in phosphate buffer at different pH using gold electrode. For analytical purpose, a well resolved irreversible adsorption controlled voltammetric peak was obtained in pH 7 phosphate buffer solution of ionic strength 0.2 M at 0.98 V for cyclic voltammetry. A linear relationship between the peak current and the orphendrine hydrochloride concentration, was obtained using differential pulse voltammetric method. The proposed method was used for its quantitative determination in pharmaceuticals and human biological fluids. The linear response was obtained in the range of 3.0×10−8 to 1.0×10−6 M with a detection limit of 7.10×10−9 M. Precision and accuracy of the developed method was checked by recovery studies. The proposed method can be used in clinical laboratories and pharmacokinetic studies.

Titanium Dioxide (TiO2) nanoparticles were synthesized by the precipitation method. The obtained products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). As synthesized TiO2 nanoparticles were used for the modification of carbon paste electrode (MCPE). Electrochemical determination of dopamine was carried out using phosphate buffer solution at pH 7.2. MCPE exhibit excellent electrochemical sensor for dopamine having high sensitivity and reproducibility. Potentially interfering compounds did not interfere for determination of DA at a surface of propose sensor in the optimum condition. The proposed sensor was successfully applied for the determination of DA in real samples such as DA in injections.

A novel all-solid-state (ASS) potentiometric poly vinyl chloride (PVC) membrane sensor is introduced, and to evaluate its applicability in the analyses of real samples it was used for monitoring of mercury ions in waste water samples. The ASS electrode is composed of a conductive composite of graphite and epoxy resin loaded with multi-walled carbon nanotubes (MWCNTs) acting as intermediary layer between an inner copper wire, and an outer thin PVC membrane which is coated on the conducting transducer. The optimal composition of the outer polymeric membrane was found to be 30% of PVC, 60% of nitro benzene (NB) as a plasticizer, 5% of an ionophore L, 2% of an ionic liquid, and 3% NaTPB. The resulting sensor showed a good Nernstian response of 29.4±0.3 mV/decade, in a rather wide range of 1.0×10-8-1.0×10-3 M of the mercury concentration and its detection limit was found to be as low as 3.2×10-9 M. The proposed electrode was also found to have good selectivity towards the target ion in the presence of a wide range of commonly occurring ionic species and was further used to determine the concentration of Hg2+ ions in waste water samples.

Calcium ferrite nanoparticles (CaFe2O4) were prepared by a solution based method using calcium chloride (CaCl2), Ferrous sulphate (FeSO4), dl serine and sodium hydroxide (NaOH) as a precipitant and the obtained precipitation was calcinated under 500 ºC for 4 h. The resulting material was characterized by using X-ray diffractometry (XRD), Energy dispersive spectroscopy (EDS) and Scanning electron microscopy (SEM). The CaFe2O4 NPs were used for the preparation of CaFe2O4 NPs/carbon paste electrode (CaFe2O4 NPs/CPE) and applied for the electrochemical investigation of dopamine (DA), uric acid (UA) and folic acid (FA) which exhibits good electrocatalytic activity for investigation of DA, UA and FA at physiological pH 7.4. The electrocatalytic currents increased linearly with an increase in DA, UA and FA concentration and the scan rate effect was studied. The modified electrode shows, overall electrode process is adsorption and diffusion controlled.

In this work, effect of accumulative roll bonding (ARB) process on the electrochemical behavior of pure copper in 0.01 M KOH solution were studied. Corrosion current density measured from potentiodynamic polarization plots, the passive film and charge-transfer resistance estimated with electrochemical impedance spectroscopy (EIS) and finally defect density drawn from Mott–Schottky analysis. Potentiodynamic polarization curves revealed that the higher number of cycles for specimens proceeds with the ARB process rather than annealing yield to lower corrosion current density. EIS results showed that as the number of ARB cycles increases, both passive film and the charge-transfer resistance increases. Mott–Schottky analysis revealed that with increasing the number of ARB cycles, the acceptor density of the passive films decreased. All electrochemical measurements showed that increasing the number of ARB cycles offer better conditions for forming the passive films.

A model of electrode reaction of solid compound that includes an insertion of cations from the solution is developed and the influence of concentration-dependent diffusion coefficient in cyclic voltammetry is investigated theoretically. Generally, the form of response does not change significantly, but in some cases the cathodic peak may split in two.

This paper describes determination of trace level of copper ions on a new type of modified glassy carbon paste electrode based on addition of different amount of Co-ferrites in glassy carbon paste (CoFeMGCPE). Co-ferrite nanoparticles with different amount of cobalt were synthesized and characterized using scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). A significant increase in current was achieved by introducing modifier in composition of the electrode in comparison with the bare glassy carbon paste electrode. Electrochemical parameters such as percentage of modifier, accumulation time and potential, pH and the optimized amount of cobalt in the ferrites were determined. The best voltammetric response was observed for Co0.5Fe0.5Fe2O4 when percentage of modifier was 3%. In acetate buffer solution, pH 4.5, thus prepared electrode displays selective detection toward copper ions, detection limit of 96 nM and it was successfully applied for the determination of copper ions in natural water samples, with satisfactory recovery.

Polyvinyl chloride (PVC) membrane sensor is described and characterized for the determination of a Benzodiazepine drug; bromazepam (BMZ). The sensor based on the use of the ion association complex of BMZ cation with tetraphenyl borate (BMZ-TPB) counter anion as ion exchange sites in the PVC matrix plasticized with dibutylsebathete (DBS) as a solvent mediator. The performance characteristics of thissensor were evaluated according to IUPAC recommendations; achieve a fast, stable and linear response for BMZ over the concentration range 10–6 to 10–2 M with slope of 44.13 mV per concentration decade. The direct potentiometric determination of BMZ using the proposed sensor gave average recovery of 100.05±0.66. The sensor is used for determination of BMZ in pharmaceutical formulations and in plasma. Validation of the method shows suitability of the proposed sensor for use in the quality control assessment of BMZ. The developed method was proved to be simple, accurate and precise when statistically compared with a reference HPLC method.