No abstract

Electrochemical behavior of disopyramide (DPA) and optimum conditions to its quantitative determination were investigated using voltammetric methods. Some electrochemical parameters such as diffusion coefficient, surface coverage of adsorbed molecules, electron transfer coefficient, standard rate constant and number of electrons were calculated using the results of cyclic and square-wave voltammetry. All studies were based on the quasi-reversible and adsorption-controlled electrochemical reduction signal of DPA at about -1.60 V vs Ag|AgCl at pH 10.0 in Britton-Robinson buffer. This adsorptive character of molecule was used to develop fully validated, new, rapid, selective and simple square-wave cathodic adsorptive stripping voltammetric (SWCAdSV) method to the direct determination of DPA in pharmaceutical dosage forms and biological samples without time-consuming steps prior to drug assay. Peak current of electrochemical reduction of DPA was found to change linearly with the concentration in the range from 7.15 × 10 -8 mol l -1 (0.024 mg l -1 ) to 1.43 × 10 -6 mol l -1 (0.49 mg l -1 ). Limit of detection (LOD) and limit of quantification (LOQ) were found to be 5.65 × 10 -8 mol l -1 (0.019 mg l -1 ) and 1.88 × 10 -7 mol l -1 (0.064 mg l -1 ), respectively. The method was successfully applied to assay the drug in tablets, human serum and human urine with good recoveries at about 100%.

A comparison of the analytical characteristics of two tyramine biosensors, based on graphene oxide (GRO) and polyvinylferrocene (PVF) modified screen‐printed carbon electrodes (SPCE), is reported. Diamine oxidase (DAOx) or monoamine oxidase (MAOx) was immobilized onto the PVF/GRO modified SPCE to fabricate the biosensors. Surface characteristics and electrochemical behaviour of the modified SPCEs were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and cyclic voltammetry (CV). Electrode surface composition and experimental variables such as pH and working potential were optimized in order to ensure a high performance. Under optimum experimental conditions, both DAOx/PVF/GRO/SPCE and MAOx/PVF/GRO/SPCE biosensors exhibited wide linear dynamic ranges for tyramine from 9.9×10−7 to 1.2×10−4 M and from 9.9×10−7 to 1.1×10−4 M, respectively. MAOx/PVF/GRO/SPCE biosensor showed higher sensitivity (11.98 μA mM−1) for tyramine determination than the DAOx/PVF/GRO/SPCE biosensor (7.99 μA mM−1). The substrate specifity of the biosensors to other biogenic amines namely histamine, putrescine, spermine, spermidine, tryptamine, β‐phenylethylamine and cadaverine was also investigated. The developed biosensors were successfully used for tyramine determination in cheese sample.

Amperometric lactate biosensor based on a carbon paste electrode modified with benzo[c]cinnoline and multiwalled carbon nanotubes is reported. Incorporation of benzo[c]cinnoline acting as a mediator and multiwalled carbon nanotubes providing a conduction pathway to accelerate electron transfer due to their excellent conductivity into carbon paste matrix resulted in a high performance lactate biosensor. The resulting biosensor exhibited a fast response, high selectivity, good repeatability and storage stability. Under the optimal conditions, the enzyme electrode showed the detection limit of 7.0×10−8 M with a linear range of 2.0×10−7 M–1.1×10−4 M. The usefulness of the biosensor was demonstrated in serum samples.

The electrochemical properties of montelukast sodium (MKST) at zinc oxide nanoparticles modified carbon paste electrode were investigated by cyclic voltammetry and square wave voltammetry. All studies were based on the irreversible and adsorption-controlled electrochemical reduction signal of montelukast sodium at about -0.7 vs. Ag/AgCl at pH 2.3 in methanol-Britton-Robinson buffer mixture. This adsorptive character of the molecule was used to develop a novel, validated, rapid, selective and simple square wave cathodic adsorptive stripping voltammeric method for the direct determination of montelukast sodium in pharmaceutical and biological fluids without time-consuming steps prior to drug assay. Peak current of electrochemical reduction of montelukast sodium was found to vary linearly with the concentration in the range from 1.0 × 10 -8 to 1.28 × 10 -6 mol L -1 . In this method, limit of detection was found to be 7.7 × 10 -9 mol L -1 . The method was applied to determine the content of MKST tablet and spiked human serum.

2-[(8-Hydroxyquinoline-5-yl)azo]benzo[c]cinnoline (HQAB) was prepared and characterized by elemental analysis, MS, FTIR and 1 H NMR techniques. The electrochemical reduction of HQAB has been investigated by cyclic voltammetry, chronoamperometry and controlled potential electrolysis at mercury pool electrode in the pH range 3.5-9.4. The number of electrons transferred in the electrode reaction, diffusion coefficients and standart rate constants were calculated. In acidic medium, cyclic voltammograms display four cathodic peaks, with the total exchange of 6 e -and 6 H + . By contrast, the reverse scan displays two anodic peaks. Constant potential electrolysis at -1.0 V and TLC analysis of the product reveals that the reduction of azo group (in the bridge) in HQAB does not stop at the hydrazo stage but goes further through the cleavage of -NH-NH-linkage to give amino compounds as the final products. The voltammograms recorded in basic medium exhibit two cathodic peaks corresponding to 4 e -, 4 H + and two reverse anodic peaks, and thus the reduction stopped at hydrazo stage. A tentative mechanism for the reduction has been suggested.Azo dyes are perhaps, among the most extensively studied classes of organic compounds both from theoretical and practical viewpoints. The major reason for this is that their widespread use as chromophoric and metallochromic reagents 1-3 , colorants 4-8 , non-linear optic materials 9-12 , photosensitizers 13-15 and metal sensors [16][17][18] . An azo dye bearing the 8-hydroxyquinoline and benzo[c]cinnoline moieties would be expected to display, apart from the general characteristics of the azodyes, behaviors reminiscent to both compounds. Azo dyes attached to 8-hydroxyquinoline

A comparison of the analytical performances of four different (bio)sensor designs in H2O2 determination is discussed. The (bio)sensor designs developed were based on the use of (i) multiwalled carbon nanotubes (MWCNT), zinc oxide nanoparticles (ZnONP), prussian blue (PB); (ii) MWCNT, ZnONP, PB and ionic liquid (IL); (iii) MWCNT, ZnONP and horseradish peroxidase (HRP) and (iv) MWCNT, ZnONP, HRP and IL modified glassy carbon electrode (GCE). A performance comparison of (bio)sensors showed that the one based on HRP/IL‐MWCNT‐ZnONP/GCE showed the best analytical characteristics with a linear dynamic range of 9.99×10−8–7.55×10−4 M, detection limit of 1.37×10−8 M and sensitivity of 17.00 μA mM−1.

No abstract