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    Carbonaceous Materials-12: a Novel Highly Sensitive Graphene Oxide-Based Carbon Electrode: Preparation, Characterization, and Heavy Metal Analysis in Food Samples
    (Springer, 2016) Yavuz, Samet; Erkal, Asli; Kariper, Ishak Afsin; Solak, Ali Osman; Jeon, Seungwon; Mulazimoglu, Ibrahim Ender; Ustundag, Zafer
    Graphene oxide (GO) was covalently attached to glassy carbon (GC) electrode (GC-O-GO) for fabricating nanosensors to determine trace Pb2+ and Cd2+ using differential pulse anodic stripping voltammetry (DPASV). Surface characterization of the nanofilm-covered electrode was performed via electrochemical cyclic voltammetry (CV), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) techniques. Surface pKa of the GO covalent attached GC (GC-O-GO) was calculated via CV. Under optimal conditions, a linear response was found for Pb2+ and Cd2+ in the range from 1 x 10(-8) to 1 x 10(-12) M. The limit of detections (LODs) of Pb2+ and Cd2+ were 0.25 pM and 0.28 pM, respectively. The method shows good reproducibility, and stability was successfully applied to measure Pb2+ and Cd2+ levels in rice, soya, milk, and tap water samples, with good agreement with those obtained by the standard inductively coupled plasma optical emission spectrometry (ICP-OES) method. The method was evaluated by application with the simultaneous determination of the ions in food samples (n = 6) using the standard addition method. The recoveries of the Pb2+ and Cd2+ were up to 98 %.
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    Isophtalic acid terminated graphene oxide modified glassy carbon nanosensor electrode: Cd2+ and Bi3+ analysis in tap water and milk samples
    (Taylor & Francis Inc, 2017) Albayrak, Isa; Erkal, Asli; Yavuz, Samet; Kariper, Ishak Afsin; Mulazimoglu, Ibrahim Ender; Ustundag, Zafer
    In this study, graphene oxide was derivative with 5-aminoisophtalic acid by amidization reaction. The nanomaterial in suspension was denoted as graphene oxide-isophtalic acid. The graphene oxide-isophtalic acid suspension was covered on the glassy carbon electrode surface under the infrared lamb. The graphene oxide was characterized with transmission electron microscopy and x-ray diffraction. Surface characterization of the glassy carbon/graphene oxide-isophtalic acid was performed with x-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The ultrasensitive nanoplatform for the simultaneous electrochemical square-wave anodic stripping voltammetry assay of Bi3+ and Cd2+ in aqueous solution has been developed on the glassy carbon/graphene oxide-isophtalic acid. The linearity range of Bi3+ and Cd2+ were 1.0x10(-8) - 1.0x10(-12) M (S/N = 3). The responses of species were practically unaltered with the increase of various species concentration. The detection limits of Cd2+ and Bi3+ were determined as 8.1x10(-13) M and 1.06x10(-13) M, respectively. The electrode performance was checked with tap water and commercially milk samples.