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    Öğe
    Flow injection photoamperometric investigation of ascorbic acid using methylene blue immobilized on titanium phosphate
    (Taylor & Francis Inc, 2006) Dilgin, Y; Nisli, G
    Methylene blue (MB) was incorporated into titanium phosphate (TiP) after pretreatment of TiP with the gas, n-butyl amine. The dye is strongly retained and not easily leached from the layered host matrix. The adsorbed MB on TiP was used to prepare modified carbon paste electrodes (MCPE), which were studied voltammetrically and in amperometric flow injection (FI) mode for the electrocatalytic oxidation of ascorbic acid (AA). The electrochemical behavior of the immobilized dye was investigated with cyclic voltammetry, at a pH 7.0 phosphate buffer containing 0.5 M KCl, at different potential scan rates. The MB immobilized on the support underwent a quasi-reversible electrochemical redox reaction. A homemade flow-through electrochemical cell with a suitable transparent window for irradiation of the electrode surface was constructed and used for amperometric FI studies. The photoamperometric-FI conditions were optimized for sensitivity and reproducibility at a flow rate of 1.5 mL/min, a transmission tubing length of 25 cm, a sample injection volume of 100 mu L, and a constant applied potential of +100 mV vs. SCE. The calibration curve for AA was linear over the concentration range from 1.0x10(-6) to 2.5x10(-5) mol l(-1) for both amperometric and photoamperometric studies. But the slope of the photoelectrocatalytic FIA procedure was improved about 52% compared with those obtained without irradiation. The results obtained for AA determination in some pharmaceutical products are in good agreement with those obtained using the procedure involving the reaction between triiodide and AA.
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    Öğe
    Fluorimetric determination of Ascorbic Acid in Vitamin C tablets using methylene blue
    (Pharmaceutical Soc Japan, 2005) Dilgin, Y; Nisli, G
    In this study, a simple and sensitive fluorimetric method was described for the determination of Ascorbic Acid (AA). The procedure is based on the reaction between AA and Methylene Blue (MB). The fluorescence intensity of NIB was measured at excitation and emission of 664 and 682 nm, respectively. MB concentration was decreased as a function of decreasing fluorescence intensity due to forming colorless form of MB (Leuco-MB) in the reaction between AA and NIB. A linear relationship was obtained between the decreasing fluorescence intensity and the concentration of AA in the range of 3.0x10(-7)-6.0x10(-6) mol(.)l(-1). The detection limit was 2.5x10(-7) mol(.)l(-1). The proposed method was applied successfully for the determination of AA in Vitamin C tablets.
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    Öğe
    Photoelectrochemical investigation of methylene blue immobilised on zirconium phosphate modified carbon paste electrode in flow injection system
    (Elsevier Science Bv, 2005) Dilgin, Y; Dursun, Z; Nisli, G; Gorton, L
    The adsorption of methylene blue (MB) onto zirconium phosphate (ZrP) was studied and the adsorption capacity value and isotherms were determined. The adsorption capacity of ZrP was increased after being exposed to gas phase n-butyl amine. The adsorbed MB on ZrP was used as a modifier material in carbon paste electrode (MCPE), which in turn was used in voltammetric investigations and flow injection (FI) amperometric determination of ascorbic acid (AA). A quasi-reversible electrode reaction of adsorbed MB was exhibited. A home made flow-through electrochemical cell with a suitable transparent window for irradiation of the electrode surface was constructed and used for amperometric FI studies. The photoamperometric-FI conditions were optimised as 1.5 mL min(-1) flow rate, a 25 cm transmission tubing length, a 100 mu L injection volume, and a constant applied potential of +100 mV versus SCE. The calibration curve for AA was linear over the concentration range from 1.0 x 10(-6) to 4.0 x 10(-5) M. The relative standard deviation of four replicate injections of 3.0 x 10(-5) M AA was 1.2 %. The results obtained for AA determination in pharmaceutical products are in good agreement with those obtained using the procedure involving the reaction between triiodide and AA. (c) 2005 Elsevier B.V. All rights reserved.