Topcu, Cihan; Coldur, Fatih; Caglar, Bulent; Ozdokur, K. Volkan; Cubuk, Osman

A novel solid-state electrochemical sensor based on a newly synthesized cross-linked copper(II) doped-copolymer and carbon nanotube material was developed for the direct determination of monohydrogen phosphate ions (HPO42−). The synthesized copolymers were characterized by FTIR, XPS, TG/DTG-DTA and SEM techniques. The sensor had a Nernstian slope:-30.7±0.4 mV/decade, linear concentrations range: 1.0×10−6 - 1.0×10−1 M, detection limit: 6.5×10−7 M, response time: 4 s and life time: 17 weeks. The sensor displayed constant potentials in the pH range 7.0-9.5. The sensor was successfully used as an indicator electrode in potentiometric titration and the direct determination of HPO42− in water samples.

Akoğulları, Seçil; Çιnar, Seda; Özdokur, Kemal Volkan; Aydemir, Tülin; Ertaş, Fatma Nil; Koçak, Süleyman

Present study describes the synthesis of mixed oxide films of manganese and vanadium by electrochemical pulsed deposition technique on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The film was further decorated with gold nanoparticles to enhance the reduction signal of dissolved oxygen in pH 5.17 acetate buffer solution. All of the electrochemical synthesized modified electrodes have been characterized with Scanning electron microscopy(SEM), High-resolution transmission electron microscopy (HRTEM), X-Ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD) techniques. The electrode obtained (AuNPs/MnOx−VOx/CNT/GCE) was utilized as a platform for glucose biosensor where the glucose oxidase enzyme was immobilized on the composite film with the aid of chitosan and an ionic liquid. The electrochemical performance of the biosensor was investigated by cyclic voltammetry and the relative parameters have been optimized by amperometric measurements in pH 5.17 acetate buffer solution. The developed biosensor exhibited a linear range for glucose between 0.1–1.0 mM and the limit of detection was calculated as 0.02 mM.

Özdokur, K. Volkan

Copper oxide decorated multi-walled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE) was prepared for determination of isoniazid (INZ) in various matrices. The electrochemical behavior of INZ was tested with the aid of Cyclic Voltammetry (CV) and quantitative experiments were performed by using Linear Sweep Voltammetry (LSV). Morphological and structural characterization of the modified electrode was performed by utilizing Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS) while electrochemical characterization was performed by using CV and Electrochemical Impedance spectroscopy (EIS). The proposed sensor exhibited well defined anodic peak at 0.30 V for INZ at pH 6.0 medium. Under the optimum conditions, a linear relation between INZ concentration and peak current was observed in the range of 2.0×10−7 to 5.0×10−5 M. Limit of detection was calculated as 1.0×10−8 M and repeatability and accuracy was found as 5.60 % and 91.0 % for 5.0 10−7 M INZ by using 3 successive measurement, respectively. Then, the analytic performance of the electrode developed was tested by analyzing commercial tablets, artificial human serum and urine samples. The results indicated that satisfactory recoveries was observed for all issue.

Özdokur, Kemal Volkan; Koçak, Çağrı Ceylan

A system of Pt nanoparticles and poly(ortho-phenylenediamine) film electrochemically deposited onto a glassy carbon electrode (GCE/PoPD/Pt) was fabricated. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and atomic force microscopy techniques were used to identify the surface characteristics of the composite electrode. The conductive polymers and Pt nanoparticles together resulted in a synergistic effect, and the new formed surface was highly active against polyphenolic structures. Rosmarinic acid (RA) and protocatechuic acid (PCA) are phenolic compounds found in plants, and they are used in many applications, particularly as pharmaceuticals. The GCE/PoPD/Pt was used for the simultaneous determination of RA and PCA in a pH 2.0 H2SO4 solution for the first time. The RA and PCA concentrations were determined using differential pulse voltammetry (DPV) and chronoamperometry. By the amperometry measurement, for RA and PCA, a linear relation was observed in the concentration ranges of 1–55 μmol L−1 and 1–60 μmol L−1, with detection limits of 0.5 μmol L−1 and 0.6 μmol L−1, respectively. In the simultaneous determination with DPV, the detection limits for both RA and PCA were calculated as 0.7 μmol L−1. The GCE/PoPD/Pt was successfully used for the simultaneous determination of RA and PCA in a real sample, and its accuracy was verified by high-performance liquid chromatography studies.

Coldur, Fatih; Andac, Muberra

A potentiometric flow injection system was adopted by using a Li+-selective electrode with improved selectivity for sensitive and selective determination of Li+ in human serum spiked samples. For the optimization of the offered flow injection system, multivariate method was utilized. Potentiometric characteristics of the system were investigated (linear range: 5.0×10-5-1.0×10-1molL-1, slope: 56.93mV per decade, detection limit: 3.4×10-5molL-1, sampling-rate: 40 injections per hour). The detection of Li+ in real serum samples was achieved. The obtained results for the spiked serum samples were in good agreement with IC results at 95% confidence level.