Browsing by Author "Keskin, E."

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Electrochemical Determination of Norepinephrine by Adsorptive Stripping Voltammetry Using a Bare Boron-Doped Diamond Electrode
(Editura Academiei Romane, 2019) Keskin, E.; Yardim, Y.; Levent, A.; Şentürk, Z.
A boron-doped diamond electrode was used for the first time for sensitive and selective analysis of norepinephrine (NE) using square wave voltammetry (SWV) technique. NE displayed one well-defined, irreversible and adsorption-controlled oxidation peak at about +0.85 V (vs. Ag/AgCl) in Britton-Robinson buffer (BR, 0.1 M, pH 2.0) using cyclic voltammetry (CV) technique. The effect of supporting electrolyte, solution pH and instrumental variables on oxidation peak current were optimized. In optimal experiment conditions, it was found that there was an excellent correlation between oxidation peak current and NE concentration in the range of 1 to 100 μg mL-1 (4.9×10-6 M-4.9×10-4 M) with a detection limit of 0.254 μg mL-1 (1.2×10-6 M) in 0.1 M BR buffer (pH 2.0) solution employing square-wave stripping mode. The developed technique can be used for the quantification of NE in the pharmaceutical formulation with acceptable recoveries. © 2020 Elsevier B.V., All rights reserved.
Voltammetric Studies on the Potent Carcinogen, 7,12-Dimethylbenz[a]anthracene: Adsorptive Stripping Voltammetric Determination in Bulk Aqueous Forms and Human Urine Samples and Detection of Dna Interaction on Pencil Graphite Electrode
(Elsevier, 2010) Yardim, Y.; Keskin, E.; Levent, A.; Ozsoz, M.; Senturk, Z.
7,12-Dimethylbenz[a]anthracene (DMBA), is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a very potent carcinogen. Initially, the electrochemical oxidation of DMBA at the glassy carbon and pencil graphite electrodes in non-aqueous media (dimethylsulphoxide with lithium perchlorate) was studied by cyclic voltammetry. DMBA was irreversibly oxidized in two steps at high positive potentials, resulting in the ill-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure on disposable pencil graphite electrode in aqueous solutions over the pH range of 3.0-9.0. The response was characterized with respect to pH of the supporting electrolyte, pre-concentration time and accumulation potential. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in acetate buffer, pH 4.8 at +1.15V (vs. Ag/AgCl)(a pre-concentration step being carried out at a fixed potential of +0.60 V for 360 s). The process Could be used to determine DMBA concentrations in the range 2-10 nM, with an extremely low detection limit of 0.194 nM (49.7 ng L-1). The applicability to assay of spiked human urine samples was also illustrated. Finally, the interaction of DMBA with fish sperm double-stranded DNA based on decreasing of the oxidation signal of adenine base was studied electrochemically by using differential pulse voltammetry with a pencil graphite electrode at the surface and also in solution. The favorable signal-to-noise characteristics of biosensor resulted in low detection limit (ca. 46 nM) following a 300-s interaction. These results displayed that the electrochemical DNA-based biosensor could be used for the sensitive, rapid. simple and cost effective detection of DMBA-DNA interaction. (C) 2009 Elsevier B.V. All rights reserved.