Bensu Ertek

Amperometric determination of sulfide based on its electrocatalytic oxidation at a pencil graphite electrode modified with quercetin

This study describes a new approach for the investigation of electrocatalytic oxidation of sulfide using a pencil graphite electrode modified with quercetin (PGE/QH(2)). Adsorption procedure was used for the preparation of the modified electrodes. It was observed that PGE/QH(2) showed a significant electrocatalytic activity toward sulfide oxidation. Cyclic voltammetric studies show that the peak potential of sulfide shifts from +450 mV at bare PGE to +280 mV at PGE/QH(2). The electrocatalytic currents obtained from amperometric measurements at +300 mV vs. Ag/AgCl/KCl(sat) and at pH 8.0 BR buffer solution containing 0.1M NH(4)Cl were linearly related to the concentration of sulfide. The calibration graph consisted of two linear segments of 1-20 μM and 20-800 μM with a detection limit of 0.3 μM (based on 3s(b)). The proposed method was successfully applied to the determination of sulfide in waste waters and was compared with the spectrophotometric method.

Differential pulse voltammetric determination of eugenol at a pencil graphite electrode

In this study, the electrochemical behavior of eugenol, a widely used herbal drug, was investigated at a pencil graphite electrode (PGE). A low-cost, disposable, sensitive and selective electrochemical sensor is proposed for the determination of eugenol by recording its differential pulse voltammograms in Britton-Robinson buffer solution containing 0.1 M KCl with pH of 2.0 at the PGE. The PGE displayed a very good electrochemical behavior with significant enhancement of the peak current compared to a glassy carbon electrode. Under experimental conditions, the PGE had a linear response range from 0.3 μM to 50.0 μM eugenol with a detection limit of 0.085 μM (based on 3S(b)). Relative standard deviations of 2.4 and 4.8% were obtained for five successive determinations of 30.0 and 5.0 μM eugenol, respectively, which indicate acceptable repeatability. This voltammetric method was successfully applied for the direct determination of eugenol in real samples. The effect of various interfering compounds on the eugenol peak current was also studied.

Photoelectrochemical glucose biosensor based on a dehydrogenase enzyme and NAD+/NADH redox couple using a quantum dot modified pencil graphite electrode

A simple, disposable and economical modified electrode was prepared by electrodeposition of hybrid quantum dots (ZnS–CdS) onto a pencil graphite electrode (PGE) surface and subsequent immobilization of glucose dehydrogenase (GDH) onto the quantum dot modified electrode (GDH/ZnS–CdS/PGE). The prepared electrode was effectively used for the photoelectrochemical determination of glucose in a flow injection analysis (FIA) system using a new home-made flow cell which was designed for PGEs for the first time. Results from the cyclic voltammetric and FI amperometric measurements revealed that the GDH/ZnS–CdS/PGE is capable of signaling photoelectrocatalytic activity involving NADH when the surface of the GDH/ZnSr–CdS/PGE is irradiated with a light source with a fiber optic cable (250 W halogen lamp). The currents of NADH produced by the enzymatic reaction in the photoamperometric FIA system under optimized conditions (carrier stream: 0.1 M phosphate buffer solution (pH 7.0) containing 1.0 M KCl and 10.0 mM NAD+, applied potential: +0.8 V vs. Ag/AgCl/KCl(sat.); flow rate: 0.6 mL min−1, sample loop: 100 μL; transmission tubing length: 10 cm) were linearly correlated with the glucose concentration. Calibration curves were obtained for glucose concentrations within a range from 0.2 to 8.0 mM. The detection limits were found to be 0.09 and 0.05 mM for the amperometric and photoamperometric methods, respectively. The relative standard deviations (n = 7) for 0.5 mM glucose were 4.5% and 3.5% from the photoamperometric and amperometric results respectively. The photoelectrochemical biosensor was applied to real samples successfully. The results with this biosensor showed good selectivity, repeatability and sensitivity for monitoring glucose in amperometric and photoamperometric FIA studies.

Voltammetric Determination of Tannic Acid in Beverages using Pencil Graphite Electrode

Vu D.L., Ertek B., Dilgin Y., Cervenka L. (2015): Voltammetric determination of tannic acid in beverages using pencil graphite electrode. Czech J. Food Sci., 33: 72-76. The pretreated pencil graphite electrode (Pre-PGE) prepared by a chronoamperometry technique was applied for the determination of tannic acid using anodic stripping differential pulse voltammetry. The currents obtained from voltammetry measurements at optimum conditions were linearly correlated with the concentration of tannic acid. Calibration curve was obtained for tannic acid in the concentration range of 5.0-500 × 10 -9 mol/l. The limit of detec - tion was found to be 1.5 × 10 -9 mol/l. The content of tannic acid in beverage samples determined with Pre-PGE was in good agreement with that obtained by the standard spectrophotometric method.

Photoamperometric flow injection analysis of glucose based on dehydrogenase modified quantum dots-carbon nanotube nanocomposite electrode

In this work, a core-shell quantum dot (QD, ZnS-CdS) was electrodeposited onto multiwalled carbon nanotube modified glassy carbon electrode (ZnS-CdS/MWCNT/GCE) and following glucose dehydrogenase (GDH) was immobilized onto QD modified electrode. The proposed electrode (GDH/ZnS-CdS/MWCNT/GCE) was effectively used for the photoelectrochemical biosensing of glucose in flow injection analysis (FIA) system using a home-made flow cell. Results from cyclic voltammetric and FI amperometric measurements have revealed that GDH/ZnS-CdS/MWCNT/GCE is capable of signaling photoelectrocatalytic activity toward NADH when the surface of enzyme modified electrode was irradiated with a light source (250W Halogen lamp). Thus, photoelectrochemical biosensing of glucose was monitored by recording current-time curve of enzymatically produced NADH at optimized conditions. The biosensor response was found linear over the range 0.010-2.0mM glucose with detection limits of 6.0 and 4.0μM for amperometric and photoamperometric methods, respectively. The relative standard deviations (n=5) for 0.5mM glucose were 5.8% and 3.8% for photoamperometric and amperometric results, respectively. The photoelectrochemical biosensor was successfully applied to the real samples. The results with this biosensor showed good selectivity, repeatability and sensitivity for monitoring glucose in amperometric and photoamperometric FIA studies.

Determination of anti-cancer drug emodin using a silica-gel-modified carbon paste electrode

In this paper, a silica-gel-modified carbon paste electrode (Si-gel/CPE) was used to determine the anti-cancer drug emodin by anodic stripping differential pulse voltammetry (ASDPV). The effects of the silica-gel content, the pH of the supporting electrolyte, and the scan rate on the oxidation current of emodin were investigated. The oxidation currents of emodin obtained from ASDPV measurements were linearly correlated with the concentration in the range of 5.0 × 10-9 to 300.0 × 10-9 mol L-1. The limit of detection was determined to be 1.5 × 10-9 mol L-1. The current method was successfully applied to determine emodin in a knotweed root sample, with recovery rate of 92.5% to 98.3%.