Browsing by Author "Alpar, Nurcan"

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Grafen-modifiye Elektrotların İlaçlarda ve Gıda Örneklerinde İki Yeni Uygulaması. Bor-katkılı Elmas Elektrotla Kıyası
(2016) Levent, Abdulkadir; Çelebi, Metin; Yiğit, Aydın; Şentürk, Zühre; Yardım, Yavuz; Alpar, Nurcan
A Graphene-Based Electrochemical Sensor for the Individual, Selective and Simultaneous Determination of Total Chlorogenic Acids, Vanillin and Caffeine in Food and Beverage Samples
(Wiley-v C H verlag Gmbh, 2018) Yigit, Aydin; Alpar, Nurcan; Yardim, Yavuz; Celebi, Metin; Senturk, Zuehre
An electrochemical sensor based on the electrocatalytic activity of graphene (GR) was prepared, and used for the individual, selective and simultaneous determination of 5-O-Caffeoylquinic acid (5-CQA) that is major compound of chlorogenic acids in coffee, vanillin (VAN) and caffeine (CAF). The electrochemical behaviors of these compounds on GR modified glassy carbon electrode (GR/GCE) were investigated by cyclic voltammetry and square-wave adsorptive stripping voltammetry. By using stripping conditions after 30s accumulation under open-circuit voltage, the electrochemical oxidation peaks appeared at +0.53, 0.83 and 1.39V in phosphate buffer pH2.5, and good linear current responses were obtained with detection limits of 4.4x10(-9), 5.0x10(-7), and 3.0x10(-7)M for 5-CQA, VAN and CAF, respectively. The potential applicability of the proposed method was illustrated in commercial food and beverage samples.
Selective and Simultaneous Determination of Total Chlorogenic Acids, Vanillin and Caffeine in Foods and Beverages by Adsorptive Stripping Voltammetry Using a Cathodically Pretreated Boron-Doped Diamond Electrode
(Elsevier Science Sa, 2018) Alpar, Nurcan; Yardim, Yavuz; Senturk, Zuhre
The present study describes a convenient method for the selective and simultaneous determination of 5-O-Caffeoylquinic acid (5-CQA) that is major compound of chlorogenic acids (CGAs) in coffee, vanillin (VAN) and caffeine (CAF) at an unmodified boron-doped diamond (BDD) electrode using square-wave adsorptive stripping voltammetry. The effect of pretreatment (anodically or cathodically) of BDD electrode was investigated in detail on the stripping voltammetric performance for all compounds. Cathodic pretreatment was found to be best choice with respect to better peak potential separation and higher peak current intensity. Three very well-resolved and reproducible oxidative processes of 5-CQA, VAN and CAF were found at +0.68, 1.15 and 1.50 V (after 60 s accumulation under open-circuit voltage), respectively, in 0.1 M HNO3. Linear calibration plots were obtained for simultaneous determination of 5-CQA, VAN and CAF in the concentration ranges of 2.8 x 10(-6)-1.7 x 10(-4), 3.3 x 10(-6)-3.3 x 10(-4), and 5.2 x 10(-7)-2.1 x 10(-4) M, with detection limits of 4.0 x 10(-7), 3.8 x 10(-7), and 1.5 x 10(-7) M, respectively. The potential applicability of the proposed method was illustrated in commercial food and beverage samples. As far as it could be verified, the proposed analytical method is the first one based on the simultaneous determination of 5-CQA, VAN and CAF. (c) 2017 Published by Elsevier B.V.
Voltammetric Method for the Simultaneous Determination of Melatonin and Pyridoxine in Dietary Supplements Using a Cathodically Pretreated Boron-Doped Diamond Electrode
(Wiley-v C H verlag Gmbh, 2017) Alpar, Nurcan; Pinar, Pinar Talay; Yardim, Yavuz; Senturk, Zuehre
The simultaneous voltammetric determination of melatonin (MT) and pyridoxine (PY) has been carried out at a cathodically pretreated boron-doped diamond electrode. By using cyclic voltammetry, a separation of the oxidation peak potentials of both compounds present in mixture was about 0.47 V in Britton-Robinson buffer, pH 2. The results obtained by square-wave voltammetry allowed a method to be developed for determination of MT and PY simultaneously in the ranges 1-100 mu g mL(-1) (4.3x10(-6)-4.3x10(-4) mol L-1) and 10-175 mu g mL(-1) (4.9x10(-5)-8.5x10(-4) mol L-1), with detection limits of 0.14 mu g mL(-1) (6.0x10(-7) mol L-1) and 1.35 mu g mL(-1) (6.6x10(-6) mol L-1), respectively. The proposed method was successfully to the dietary supplements samples containing these compounds for health-caring purposes.
Voltammetric Sensing of Triclosan in the Presence of Cetyltrimethylammonium Bromide Using a Cathodically Pretreated Boron-Doped Diamond Electrode
(Taylor & Francis Ltd, 2018) Yardim, Yavuz; Alpar, Nurcan; Senturk, Zuhre
In the present study, a simple, cheap and sensitive electrochemical method based on a cathodically pretreated boron-doped diamond (CPT-BDD) electrode is described for the detection of triclosan with the cationic surfactant (cetyltrimethylammonium bromide, CTAB) media. The oxidation of triclosan was irreversible and exhibited an adsorption controlled process. The sensitivity of the adsorptive stripping voltammetric measurements was significantly improved with addition of CTAB. Using square-wave stripping mode, a linear response was obtained for triclosan determination in Britton-Robinson buffer solution at pH 9.0 containing 2.5 x 10(-4) M CTAB at around + 0.67 V (vs. Ag/AgCl) (after 30 s accumulation at open-circuit condition). The method could be used in the range of 0.01-1.0 mu g mL(-1) (3.5 x 10(-8)-3.5 x 10(-6) M), with a detection limit of 0.0023 mu g mL(-1) (7.9 x 10(-9) M). The feasibility of the proposed method for the determination of triclosan in water samples was checked in spiked tap water.