Yazar "Gokcel, H. Ismet" seçeneğine göre listele

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    Adsorption and deposition-assisted anodic stripping voltammetry for determination of antimony(III) in presence of hematoxylin on glassy carbon electrode
    (Elsevier Science Bv, 2017) Sezgin, Hanife Vardar; Dilgin, Yusuf; Gokcel, H. Ismet
    A validated simple, reliable and sensitive adsorptive anodic stripping voltammetric procedure is suggested for the accurate determination of antimony(III) on a glassy carbon electrode (GCE) in the presence of hematoxylin (HT), used as a chemical receptor in antimony analysis for the first time. Under optimized conditions, the plot of stripping peak current versus Sb(III) concentration showed two dynamic linear ranges, 1.0x10(-4) - 0.01 mu m (R-2 =0.9986) and 0.01 - 1.0 mu m (R-2 =0.9973) with a detection limit of 9.5x10(-11) mol (11.57 ng L-1). The RSD values of intra-day precision and inter-day precision (n =5) for 5.0x10(-7) mol L-1 Sb(III) were calculated as 1.63% and 2.27%, respectively, indicating that the proposed method has a good precision. Recoveries for Sb(III) in water samples were found to be between 97% and 102% for the 5.0x10(-7) mol L-1 Sb(III), proving the reliability and accuracy of the method proposed.
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    Adsorptive anodic stripping voltammetric determination of antimony(III) on a glassy carbon electrode using rivastigmine as a new chemical receptor
    (Elsevier Science Sa, 2015) Sezgin, Hanife Vardar; Gokcel, H. Ismet; Dilgin, Yusuf
    A very simple and sensitive adsorptive anodic stripping voltammetric method was developed for determination of antimony(III) on a glassy carbon electrode (GCE), using rivastigmine (RIV) as the chemical receptor. No study on the usage of antimony(III) for metal determination as a modifier/complexing agent/chemical receptor was found in the literature review. The proposed method is based on the accumulation of the Sb-RIV complex on GCE under stirring conditions using optimized accumulation potential and time following the recording of a differential pulse (DP) voltammogram in anodic direction. The calibration graph consisted of two linear segments of 5.0 x 10(-4)-0.5 mu M (i(p)(mu A) = 7.45C(Sb(III)) (mu M) + 0.05, R-2 = 0.9974) and 0.5-2.5 mu M (i(p)(mu A) = 10.45C(Sb(III)) (mu M) - 0.76, R-2 = 0.9959) with a detection limit of 7.1 x 10(-11) mol L-1. The RSD (n = 5, intra-day) for 1.0 x 10(-6) mol L-1 Sb(III) and 5.0 x 10(-7) mol L-1 Sb(III) were calculated as 1.53% and 2.62%, respectively. Inter-day precision (n = 5) was also calculated as 2.16% for 1.0 x 10(-6) mol L-1 Sb(III), indicating that the proposed method has good precision. The spiked water sample analyses were evaluated using the described method and a good recovery of Sb(III) was obtained with results in the range from 95.0% to 97.6%. (C) 2014 Elsevier B.V. All rights reserved.
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    Electrocatalytic Oxidation of NADH Using a Pencil Graphite Electrode Modified with Hematoxylin
    (Amer Scientific Publishers, 2012) Dilgin, Yusuf; Ertek, Bensu; Kizilkaya, Bayram; Dilgin, Didem Giray; Gokcel, H. Ismet
    In the present study, the electrocatalytic oxidation of reduced p-Nicotinamide Adenine Dinucleotide (NADH) was investigated using a pencil graphite electrode modified with hematoxylin (PGE/HMT). The PGE/HMT was prepared by adsorption of HMT on the PGE via immersion of bare PGE into 1.0 mM HMT solution (in methanol) for 60 s at room temperature. Cyclic voltammetric studies show that the peak potential of NADH oxidation shifts from +450 mV at bare PGE to +200 mV at PGE/HMT. The electrocatalytic currents obtained from the amperometric measurements at +200 mV versus Ag/AgCl/KClsat and pH 7.0 phosphate buffer solution containing 0.1 M KCl were linearly related to the concentration of NADH. The calibration graph consisted of two linear segments of 0.5-10 mu M and 10-300 mu M with a detection limit of 0.2 mu M (based on 3s(b), s(b) is the standard deviation of the blank response). The amperometric measurements exhibited that the response of the modified PGE/HMT towards the oxidation of NADH is reproducible, fast, sensitive and stable. Finally, the results obtained in the present study conclusively show that PGE modified with HMT can be effectively used to detect NADH.
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    Electrocatalytic oxidation of NADH using a pencil graphite electrode modified with quercetin
    (Elsevier, 2013) Dilgin, Yusuf; Kizilkaya, Bayram; Dilgin, Didem Giray; Gokcel, H. Ismet; Gorton, Lo
    In the present study, the electrocatalytic oxidation of reduced beta nicotinamide adenine dinucleotide (NADH) was investigated using a pencil graphite electrode modified with quercetin (PGE/QH(2)). The PGE/QH(2) was prepared through two steps: (i) the pre-treatment of PGE at 1.40V vs. Ag vertical bar AgCl vertical bar KCl(sat.) in pH 7.0 phosphate buffer containing 0.1 M KCl for 60 s and (ii) adsorption of QH(2) on the PGE via immersion of PGE into a 1.0 mM QH(2) solution (in ethanol) for 60 s. Cyclic voltammetric studies show that the peak potential of NADH oxidation shifts from +500 mV at bare PGE to +300 mV at PGE/QH(2). The electrocatalytic currents obtained from amperometric measurements at +300 mV vs. Ag vertical bar AgCl vertical bar KCl(sat.) and in phosphate buffer solution at pH 7.0 containing 0.1 M KCl were linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 0.5 mu M to 100 mu M. The limit of detection was found to be 0.15 mu M. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.
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    Glassy carbon electrode modified with poly-Neutral Red for photoelectrocatalytic oxidation of NADH
    (Springer Wien, 2011) Dilgin, Didem Giray; Gligor, Delia; Gokcel, H. Ismet; Dursun, Zekerya; Dilgin, Yusuf
    A new approach is described for the photoelectrocatalytic oxidation of Reduced -Nicotinamide Adenine Dinucleotide (NADH). It is based on a glassy carbon electrode (GCE) modified with a film of poly-Neutral Red (poly-NR) that is obtained by electropolymerization. Electrochemical measurements revealed that the modified electrode displays electrocatalytic and photo-electrocatalytic activity towards oxidation of NADH. If irradiated with a 250-W halogen lamp, the electrode yields a strongly increased electrocatalytic current compared to the current without irradiation. Amperometric and photo-amperometric detection of NADH was performed at +150 mV vs. Ag/AgCl/KClsat and the currents obtained are linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 1.0 mu M to 1.0 mM for both methods. However, the slope of the current-NADH concentration curve of the photo-electrocatalytic procedure was 2-times better than that obtained without irradiation.
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    Photoelectrocatalytic determination of NADH in a flow injection system with electropolymerized methylene blue
    (Pergamon-Elsevier Science Ltd, 2011) Dilgin, Yusuf; Dilgin, Didem Giray; Dursun, Zekerya; Gokcel, H. Ismet; Gligor, Delia; Bayrak, Burcu; Ertek, Bensu
    It was firstly described that a glassy carbon electrode electropolymerized with methylene blue shows an efficient photoelectrocatalytic activity towards NADH oxidation in a phosphate buffer solution (pH 7.0). In order to perform the photoelectrocatalytic determination of NADH in a flow injection analysis (FIA) system, a home-made flow electrochemical cell with a suitable transparent window for the irradiation of the electrode surface was constructed. The currents obtained from the photoamperometric measurements in the FIA system at optimum conditions (flow rate of carrier solution, 1.3 mL min(-1): transmission tubing length, 10 cm; injection volume, 100 mu L; and constant applied potential, +150 mV vs. Ag/AgCl) were linearly dependent on the NADH concentration and linear calibration curves were obtained in the range of 1.0 x 10(-7)-2.0 x 10(-4) M. The detection limit was found to be 4.0 x 10(-8) M for photoamperometric determination of NADH. (C) 2010 Elsevier Ltd. All rights reserved.
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    Photoelectrocatalytic oxidation of NADH in a flow injection analysis system using a poly-hematoxylin modified glassy carbon electrode
    (Elsevier Advanced Technology, 2010) Dilgin, Didem Giray; Gligor, Delia; Gokcel, H. Ismet; Dursun, Zekerya; Dilgin, Yusuf
    A stable electroactive thin film of poly-hematoxylin (poly-HT) was successfully prepared on a glassy carbon electrode (GCE) surface by recording successive cyclic voltammograms of 0.3 mM HT, in a phosphate buffer solution (pH 7.0) containing 0.1 M NaNO3, in the potential range of -0.5 to +2.0 V vs. Ag/AgCl. The deposition of HT on GCE surface can be explained through the electropolymerization process. This poly-HT modified electrode exhibited a good electrocatalytic activity towards the NADH oxidation in a phosphate buffer solution (pH 7.0), and led to a significant decrease in the overpotential by more than 320 mV compared with the bare GCE. In order to perform the photoelectrocatalytic determination of NADH in a flow injection analysis (FIA) system, a home-made flow electrochemical cell with a suitable transparent window for irradiation of the electrode surface was constructed. Flow rate of carrier solution, transmission tubing length, injection volume and applied potential for the amperometric and photoamperometric FIA studies were optimized as 1.3 mL min(-1),10 cm, 100 mu L and +300 mV vs. Ag/AgCl, respectively. The currents obtained from amperometric and photoamperometric measurements in FIA system at optimum conditions were linearly dependent on the NADH concentration and linear calibration curves were obtained in the range of 1.0 X 10(-7)-1.5 X 10(-4) M and in the range of 1.0 x 10(-7)-2.5 X 10(-4) M NADH, respectively. The relative standard deviation (RH)) of six replicate injections of 6.0 x 10(-5) M NADH was calculated as 2.2% and 4.3% for the amperometric and the photoamperometric method, respectively. The limit of detection was found to be 3.0 x 10(-8) M for the photoamperometric determination of NADH. (C) 2010 Elsevier B.V. All rights reserved.
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    Photoelectrochemical glucose biosensor in flow injection analysis system based on glucose dehydrogenase immobilized on poly-hematoxylin modified glassy carbon electrode
    (Royal Soc Chemistry, 2015) Dilgin, Didem Giray; Gokcel, H. Ismet
    In this study, a photoelectrochemical glucose biosensor is presented, comprising electropolymerized hematoxylin film on poly-amidoamine (PAMAM) dendrimers adsorbed on glassy carbon electrode (polyHT/PAMAM/GCE). After immobilization of glucose dehydrogenase (GDH) onto the poly-HT/PAMAM/GCE, photoelectrochemical biosensing of glucose was investigated using cyclic voltammetry and amperometry in a flow injection analysis (FIA) system dependent on the NAD+/NADH redox coupledehydrogenase enzyme. The linear range was from 1 x 10(-5) M to 1 x 10(-3) M with a sensitivity of 0.76 mu A mM(-1) and detection limit of 3.0 mM without irradiation in the FIA system. After irradiation, the linear range was from 5 x 10(-6) M to 1 x 10(-3) M with a sensitivity of 1.90 mu A mM(-1) and a detection limit of 1.5 mM. Comparing the results obtained from irradiation of the electrode surface with those from the reaction without irradiation, the sensitivity and the detection limit increased around 2.5- and 2.0-fold, respectively. The photoelectrochemical biosensor showed good performance with high upper detection limit, acceptable repeatability, and selectivity, providing a rapid alternative method for monitoring biomolecules and extending photoelectrochemical determination in the FIA system. The proposed electrochemical and photoelectrochemical biosensor was successfully applied to determination of glucose in real samples. The results obtained from this study provide a basis for future studies in these directions.