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    A New Redox Mediator (Cupric-Neocuproine Complex)-Modified Pencil Graphite Electrode for the Electrocatalytic Oxidation of H2O2: A Flow Injection Amperometric Sensor
    (Wiley-V C H Verlag Gmbh, 2020) Emir, Gamze; Dilgin, Yusuf; Apak, Resat
    This paper introduces the cupric-neocuproine complex ([Cu(Nc)(2)](2+)) as a new redox mediator for the electrocatalytic oxidation of H2O2. For this purpose, [Cu(Nc)(2)](2+) was modified onto a disposable pencil graphite electrode (PGE) surface by using Nafion (Nf) as a cation-exchange membrane for the effective adsorption of complex. The modified electrode was prepared by immersing Nf-adsorbed PGE into [Cu(Nc)(2)](2+) complex solution (0.40 mM of Cu2+ and 0.80 mM of Nc prepared at pH 4.76 in 0.10 M acetate buffer). SEM images and EDX spectra of electrodes were presented for the elucidation of their surface morphologies. Cyclic voltammetric results showed that H2O2 was electrocatalytically oxidized at [Cu(Nc)(2)](2+)/Nf/PGE, because both the increase in current and the potential shift to a more negative direction were observed for oxidation of H2O2 at [Cu(Nc)(2)](2+)/Nf/PGE in comparison to bare PGE. Then, the electrocatalytic activity of [Cu(Nc)(2)](2+)/Nf/PGE toward H2O2 oxidation was utilized for amperometric determination of H2O2 in flow injection analysis (FIA) system. Flow injection (FI) amperometric studies showed two linear calibration ranges (1.0-1000.0 mu M (R-2=0.9958) and 1000.0-10000.0 mu M (R-2=0.9902) with a detection limit of 0.4 mu M H2O2 which is considered good for electroanalytical determinations, especially for electrocatalytic oxidation. To test the applicability of the developed FI amperometric hydrogen peroxide sensor, H2O2 contents of some relevant samples were determined.
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    A novel flow injection amperometric method for sensitive determination of total antioxidant capacity at cupric-neocuproine complex modified MWCNT glassy carbon electrode
    (Springer Wien, 2022) Ayaz, Selen; Uzer, Aysem; Dilgin, Yusuf; Apak, Resat
    A novel amperometric method is presented for the determination of total antioxidant capacity in flow injection analysis (FIA) system using copper(II)-neocuproine complex modified on Nafion-functionalized multi-walled carbon nanotube-glassy carbon electrode ([Cu(Ncp)(2)(2+)]/Nf@f-MWCNT/GCE). Cyclic voltammetric studies showed that the modified electrode exhibits a very well-formed reversible redox couple for Cu(II)-/Cu(I)-complex. In addition, the [Cu(Ncp)(2)(2+)]/[Cu(Ncp)(2)(+)] redox pair shows very good electrocatalytic activity towards the oxidation of polyphenolic compounds (PPhCs) such as trolox, catechin, and quercetin due to the enhancement of the anodic peak current of the redox couple in the presence of these analytes. This electrocatalytic oxidation current at the [Cu(Ncp)(2)(2+)]/Nf@f-MWCNT/GCE was used for flow injection (FI) amperometric determination of PPhCs. FI amperometric-time curves recorded under optimized conditions (applied potential: + 0.6 V vs. Ag/AgCl/KCl(0.10 M), flow rate: 2 mL/min) showed that the proposed electrode had a wide linear range (LR) with a very low detection limit (LOD) for PPhCs. LR and LOD were 0.5-800 and 0.2 mu M for trolox, respectively and 0.50-250 and 0.14 mu M, respectively, for both quercetin and catechin. This sensitive method was successfully applied to the amperometric measurement of total antioxidant capacity (TAC) of some herbal teas, giving compatible results with the spectrophotometric CUPRAC method. The proposed method gave higher rank to fast-reacting antioxidants; it was equally precise but had a wider linear range and lower LOD than the spectrophotometric CUPRAC assay (e.g., LOD for ascorbic acid and gallic acid were 0.07 and 0.08 mu M, respectively), and similar electroanalytical methods using the CUPRAC reagent.
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    Flow injection amperometric determination of hydrazine at a cupric-neocuproine complex/anionic surfactant modified disposable electrode
    (Elsevier, 2020) Ayaz, Selen; Dilgin, Yusuf; Apak, Resat
    Hydrazine (N2H4) is a hazardous chemical widely used as rocket propellant and industrial intermediate, therefore its sensitive and accurate analysis in environmental samples is very important. In this study, a new approach for flow injection amperometric detection of N2H4 is proposed based on its electrocatalytic oxidation at a bis(neocuproine)copper (II) chelate complex/sodium dodecyl sulfate-modified graphite pencil electrode (Cu (II)-Ncp/SDS/GPE). The proposed electrode was prepared by consecutive adsorption of anionic surfactant (SDS) and Cu(II)-Ncp onto pencil leads and the surface morphologies of electrodes prepared were elucidated by recording of their SEM images. Cyclic voltammograms (CVs) showed that Cu(II)-Ncp exhibited an excellent redox mediator property for the electrocatalytic oxidation of N2H4, because oxidation potential of N2H4 at bare GPE shifted to more negative direction with the use of Cu(II)-Ncp/SDS/GPE. Then, flow injection (FI) electroanalysis of N2H4 was performed by utilizing the electrocatalytic oxidation of N2H4 at Cu(II)-Ncp/SDS/GPE. A wide linear range (0.25-250 mu M) with a limit of detection (LOD) of 0.07 mu M and a sensitivity of 262 mu AmM(-1)cm(-2) were obtained for the FI amperometric detection of N2H4. Satisfactory recoveries were obtained for N2H4 detection in water samples, showing that this method can be accurately applied to real water samples.
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    Introductory Note to the Special Issue of Analytical Letters for the International Conference: 10th Aegean Analytical Chemistry Days (AACD 2016)
    (Taylor & Francis Inc, 2018) Apak, Resat; Dilgin, Yusuf; Arda, Aysem
    This special issue of 'Analytical Letters' is devoted to selected papers based on contributions from the 10th Aegean Analytical Chemistry Days (AACD 2016) International Meeting. The first AACD Meeting was held in Izmir-Turkey in 1998 for enhancing the scientific collaboration of analytical chemists from Aegean countries primarily comprising Turkey and Greece, but these series of conferences later evolved into a successful international event covering the entire field of analytical chemistry practiced in almost all countries. Selected papers from most of these conferences were published in the special issues of reputable journals. Specifically in this special edition, the authors have extended their conference proceedings papers and added their latest experimental results. The papers have undergone the standard review process. The AACD 2016 Conference, providing a forum among analytical chemistry researchers from many different countries, was held in eanakkale, jointly hosted by Eanakkale Onsekiz Mart University (COMU) and Istanbul University (IU). AACD 2016 combined invited lectures, parallel oral sessions and poster presentations, altogether comprising 14 invited lectures, 45 contributed oral presentations and 343 posters, and three company presentations. The selected best 40 posters were orally presented for 5 min at the 'flash poster presentation' session. The Conference Organizers are thankful to the AACD Continuation Committee, invited speakers and all presenters, authors and reviewers who were willing to share their expertise with us by submitting/reviewing the valuable contributions to this special issue, and finally to the Chief Editor of 'Analytical Letters' and Taylor & Francis who handled the complete review process.