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Öğe Application of loop atomizer for environmental samples by flame atomic absorption spectroscopy(Pergamon-Elsevier Science Ltd, 1995) Gucer, S; Karagozler, AE; Demir, M; Ozdemir, NIntroduction of sample solutions into the flame atomic absorption spectroscopy (AAS) via electrically heated metal loops notably improves the detection limits of the technique. However, because of the low melting point of platinum (1772 degrees C) application of the loop technique is limited only to sufficiently volatile elements. In this work interference encountered with a Pt-loop atomizer is reviewed and chemical interference is found to be the most important factor limiting its applications. Therefore, a separation/enrichment step in the analytical scheme is needed not only for the enrichment of the analyte itself but also to ensure that the chemical form of the analyte in both standard and sample solutions is the same. Samples of soil extracts, fertilizers, waste water of domestic origin and air samples have been chosen to demonstrate the environmental application of the loop technique.Öğe Electrochemical poly(1,3-phenylenediamine) synthesis as enzyme immobilization media(John Wiley & Sons Inc, 1998) Ekinci, E; Ogunc, ST; Karagozler, AEElectrochemical polymerization of the 1,3-phenylenediamine in the presence of glucose oxidase with KCl aqueous electrolyte at a potential of 0.800 V versus Ag-AgCl produces adherent poly(1,3-phenylenediamine) containing enzyme (glucose oxidase) film on a platinum electrode. Polymeric sensor prepared in this one-step procedure can be used to determine hydrogen peroxide formed as the result of the enzymatic reaction between glucose and glucose oxidase in the presence of O-2. The amperometric responses of the resultant enzyme electrode to glucose were rapid, reaching steady-state values within 4-5 s, and there was a linear relationship between glucose concentration and obtained current up to 6 mM. Polymeric sensor was stable for more 3 months. The glucose selectivity of enzyme electrode was determined in the presence of some interfering substances, such as lactose, sucrose, urea, uric acid, paracetamol, and ascorbic acid. Also, the effects of buffer concentration, storage conditions, and temperature on the steady-state amperometric responses were studied. Moreover, the Arrhenius activation energy for the enzymatic reaction was calculated. (C) 1998 John Wiley & Sons, Inc.Öğe Electrochemical synthesis and optimization of poly(4-methoxyphenol) film as a sensor material(John Wiley & Sons Inc, 1998) Ozden, M; Ekinci, E; Karagozler, AEThis article describes that electrochemical polymerization of 4-methoxyphenol in the presence of enzyme glucose oxidase produces adherent polymeric films containing the active enzyme onto the surface of platinum electrodes. Polymeric electrodes prepared in this one-step procedure can be operated for the glucose determination. The effects of the electrochemical polymerization parameters (for example, concentrations of monomer, electrolyte, and enzyme; film thickness; and polymerization potential) on the electrode preparation and the effects of amperometric measurement parameters (for example, pH, temperature) on the amperometric responses to the glucose of the prepared electrodes were systematically investigated, and optimal values were determined. Furthermore, glucose specificity and storage stability of the enzyme electrode were investigated. (C) 1998 John Wiley & Sons, Inc.Öğe Electrochemical synthesis and sensor application of poly(1,4-diaminobenzene)(Elsevier Science Sa Lausanne, 1996) Ekinci, E; Karagozler, AA; Karagozler, AEThis paper describes a novel polymeric matrix, poly (p-phenylenediamine), as glucose oxidase entrapment media for amperometric glucose determination. The glucose sensor was constructed in a one-step procedure by anodic electropolymerization of p-phenylenediamine and concomitant incorporation of glucose oxidase at a potential of 0.7 V versus Ag/AgCl. Results show that the new glucose sensor has a linear range up to 6 mM, fast response time (less than 4 s) and high sensitivity. The specificity of the enzyme electrode for possible interfering species such as lactose, sucrose and urea was tested, and no discernible anodic signal was detected above the background current. Moreover, the effects of pH and temperature on the amperometric response were systematically investigated and the activation energy for enzymatic reaction was calculated as 41 kJ/mol. Also, the biosensor was found to be stable for more than 30 days.Öğe Investigation and comparison of the electrochemical behavior of some organic and biological molecules at various conducting polymer electrodes(Elsevier Science Bv, 1997) Erdogdu, G; Karagozler, AEElectrodes modified by the electrodepozition of conducting organic polymers such as poly(3-methylthiophene)(PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of some organic and biological molecules. The electrochemical behaviors of catechol, ascorbic acid, hydroquinone, dopamine, epinephrine, acetaminophen and p-aminophenol were examined by differential pulse voltammetry. The electrochemical behavior of these molecules at different electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of these compounds. Electrocatalytic 'efficiency' decreases in order of poly-3-methylthiophene, polypyrrole and polyaniline. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of most of the these compounds. The responses of the polymer electrode were 5-15 times larger as compared with those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 10(-8)-10(-9) M were achieved using the PMT, compared with 10(-6)-10(-8) M using platinum electrodes In the flow injection analysis, with increasing molecular weight of analyte molecules was to observe decreased peak heights. (C) 1997 Elsevier Science B.V.Öğe Preparation and properties of polybenzidine film-coated electrode as an H2O2 selective polymeric material(Wiley, 1998) Ekinci, E; Ozden, M; Turkdemir, MH; Karagozler, AEBy means of electrochemical polymerization, polybenzidine-modified electrodes were prepared in an aqueous monomer solution at a potential of 0.7 V versus Ag/AgCl. The permselective character of the polybenzidine electrode prepared in a one-step procedure was examined for electroactive (ascorbic acid, oxalic acid, and hydrogen peroxide) and nonelectroactive (lactose, sucrose, and urea) species. Influence of the various parameters on the permselective properties of the polybenzidine membrane was systematically investigated and the optimal values for these parameters were determined. It has been found that polybenzidine membrane showed selective permeation for hydrogen peroxide while blocking the permeation of electroactive and nonelectroactive interferents through film. In brief, it is claimed that this polybenzidine film can be used as a coating material to prevent interferences in electrochemical biosensor applications. (C) 1998 John Wiley & Sons, Inc.Öğe The preparation and sensor application of poly(p-aminophenol)(Vch Publishers Inc, 1996) Ekinci, E; Karagozler, AA; Karagozler, AEAn amperometric biosensor for glucose based on a novel polymeric matrix is described. The sensor was prepared by electrochemical polymerization of p-aminophenol in the presence of glucose oxidase on Pt substrates in a KCl solution at a potential of 0.6 V (vs. Ag/AgCl). The chronoamperometric response of poly(p-aminophenol)-glucose oxidase biosensor to hydrogen peroxide formed as the result of enzymatic reaction was measured at a potential of 0.7 V (vs. Ag/AgCl) in PBS solution. It was shown that a biosensor prepared by this onestep procedure has a linear range up to 6 mM glucose, a response time less than 5 s and a lifetime around 15 days. The sensitivity of the electrode was superior to that of much publicized polypyrrole based glucose oxidase electrode. Also, the substrate selectivity of PAP/GOx electrode was tested for coexisting substances such as lactose, sucrose, urea, paracetamol, uric and ascorbic acid and no discernible anodic response was observed above the background current.Öğe Simplex optimization of reaction variables in the production of cobalt(III) acetate in a bipolar packed-bed reactor(Elsevier Science Bv, 1996) Sener, E; Karagozler, AE; Pekel, ATCobalt(III) acetate production in a bipolar-packed bed reactor was investigated in terms of conversion ratio of Co(II) acetate, current yield and energy consumption. An experimental optimization was performed on the conversion ratio by the use of a sequential simplex method; cell voltage, concentrations of Co(II) acetate and sodium acetate, water content of the solution, temperature and the Faraday number of charge per mole of Co(II) acetate were chosen as reaction variables. The maximum conversion ratio in 36 electrolyses was 71.6% which could not be further improved by changing the levels of the selected variables. A record of the other performance parameters showed that the conditions for the highest conversion ratio were also suitable for satisfactory current and energy yields.Öğe Synthesis and optimization of permselective polymer (polyindoline) film(Springer Verlag, 1998) Ozden, M; Ekinci, E; Karagozler, AEA polyindoline permselective polymer film was readily synthesized by an electrochemical polymerization of indoline in an aqueous solution of KCl at a potential of 0.4 V vs Ag/AgCl. The amperometric responses of the polyindoline film-coated platinum electrodes to electroactive (ascorbic acid, oxalic acid and hydrogen peroxide) and non-electroactive (lactose, sucrose and urea) substances were measured at a potential of 0.7 V. Effects of various variables such as film thickness, concentrations of monomer and electrolyte, and pH on the permselective behavior of the polymeric membrane were systematically investigated and the optimal values were determined. It was found that permselective polyindoline-coated electrodes prepared in this one-step procedure permitted hydrogen peroxide oxidation while it prevented interference due to oxidizable species such as ascorbic acid and oxalic acid. As a result, it is believed that this polymeric membrane, owing to its permselective character, can be used as the protective material in the construction of hydrogen peroxide-based biosensors.Öğe Voltammetric resolution of ascorbic acid and dopamine at conducting polymer electrodes(Marcel Dekker Inc, 1996) Erdogdu, G; Mark, HB; Karagozler, AEElectrochemical behavior of dopamine and ascorbic acid binary mixture was examined by cyclic voltammetry and the analysis of a each component was performed by differential pulse voltammetry. The electrochemical behavior of these molecules on poly-3-methylthiophene, polypyrrole, polyaniline electrodes were compared. The effects of electrolyte type and its pH, and the film thickness on the voltammetric resolution of these molecules were systematically examined. At all the modified electrodes both dopamine and ascorbic acid peaks shifted their positions to more negative potentials with increasing pH, difference between the positions remaining almost constant. Type of electrolyte seems to have an effect on ascorbic acid peak only at the poly-3-methylthiophene electrode. The effect of increasing film thickness was to observe increased peak heights.
