Digitální knihovnaUPCE
 

03 (1997) Scientific papers, Series A

Permanentní URI k tomuto záznamuhttps://hdl.handle.net/10195/38113

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199721

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  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Contemporary trends in analytical electrochemistry. Assessment and prospects
    (Univerzita Pardubice, 1997) Kalvoda, Robert
    The aim of this article is to give, after a brief assessment of electroanalytical methods, an outlook on their future applications not only in usual or trivial chemical analysis but mainly in biosciences having the highest priority for us and the whole nature.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Biosensors based on carbon paste electrodes using immobilized dehydrogenase enzymes. An overview and trends
    (Univerzita Pardubice, 1997) Lobo-Castañón, Maria Jesus; Alvarez-Crespo, Suzana L.; Alvarez-Gonzalez, Maria Isabel; Saidman, Silvana B.; Miranda-Ordieres, Arturo José; Tunon-Blanco, Paulino
    Amperometric biosensors based on two different NADH catalytic systems are presented. Common to both types is the design strategy which consists in the direct mixing of the NAD' -dependent dehydrogenase enzymes and other modifying molecules with the carbon paste combined with physical barriers like dialysis membranes or conducting polymers. One type is based on the use of a redox mediator (the phenothiazine dye Toluidine Blue O) to make possible the electrocatalytic oxidation of the enzymatically produced NADH at potentials close to 0 V. The second type is based on the use of the electrochemically generated conducting polymers poly(o-aminophenol) (PAP) and poly(o­phenylenediamine) (PPD), which allow not only the immobilization of enzyme and cofactor at the electrode surface but also the amperometric detection of NADH at potentials as low as 0 V without other immobilized electron transfer mediators. An ethanol biosensor based on the first catalytic system and ethanol, lactate and glutamate sensors based on the second one are presented.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    The effect of various polyelectrolytes on alcohol oxidase/horseradish peroxidase/ferrocene modified carbon paste electrodes
    (1997) Larsson, Niklas; Gorton, Lo
    Two enzyme based alcohol biosensors were constructed by co-immobilizing alcohol oxidase and horseradish peroxidase into a carbon paste matrix. The effects of chemically modifying HRP, adding a mediator and different polyelectrolytes were examined, aiming at better operational stability when used in a flow injection system. The electrodes are characterized (sensitivity, detection limit, operational stability) when operated at an applied working potential of −50 mV vs. Ag/AgCl.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Determination of hydrogen peroxide with sensors based on heterogenous carbon materials modified with manganese dioxide
    (Univerzita Pardubice, 1997) Schachl, Klemens; Alemu, Hailemichael; Kalcher, Kurt; Ježková, Jitka; Švancara, Ivan; Vytřas, Karel
    Three different types of MnO2-modified electrodes were investigated on their electrochemical response towards hydrogen peroxide: a bulk-modified carbon paste electrode, a film-modified carbon paste electrode and a film-modified screen printed electrode. The sensors were characterized by voltammetric (cyclic voltammetry, linear sweep voltammetry) and amperometric methods (stationary and flow conditions). The best responses were obtained with a MnO2 film­modified screen printed carbon electrode which could be used as an electrochemical detector in flow injection analysis (FIA) using a NH3/NH4Cl buffer (0.2 M, pH 9.5) as a carrier. With FIA a detection limit (3σ) of 0.26 µg 1−1 could be achieved; the peak current was linear to the H2O2 concentration from 1 to 200.000 µg 1−1. The method could be successfully applied to the determination of H2O2 in various samples (cosmetic and medical products, rain water). With flow injection a sample frequency of 60 h−1 can be achieved.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Recent progress in the development of electrochemical carbon paste sensors
    (Univerzita Pardubice, 1997) Kalcher, Kurt; Schachl, Klemens; Švancara, Ivan; Vytřas, Karel; Alemu, Hailemichael
    In this review an overview is given of some recent trends in developing electrochemical sensors that are based on heterogeneous carbon materials. Their main characteristic is a usually non-conducting liquid or solid matrix, into which conductive carbon particles are embedded. Typical representatives of such types of sensors are carbon paste electrodes (CPE), solid carbon composite electrodes (CCE), and screen printed carbon electrodes (SPCE). Main emphasis in this article is put on summarizing trends and strategies of the development of carbon paste sensors during the past few years (365 references).
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Voltammetric determination of heavy metals in natural waters and biological samples by using a chemically modified carbon paste electrode
    (Univerzita Pardubice, 1997) Iliadou, Efterpi N.; Girousi, Stella T.; Voulgaropoulos, Anastasios N.; Vytřas, Karel
    The behaviour of copper, lead and cadmium was studied with a new chemically modified carbon paste electrode, with different supporting electrolytes (HCl, HClO4, H2SO4, NH3-NH4Cl). The optimum conditions for the determination of the above mentioned metals were studied either separately or simultaneously in mixtures of 2 or 3 of them. The method for their simultaneous determination was more sensitive after deposition of a mercury film "in situ" after addition of Hg(II). Detection limits are 5.00 µg l−1, 7.00 µg l−1, 2.00 µg l−1 for copper, cadmium and lead, respectively. The relative standard deviation at a concentration level of 6.00–7.50 ppb, varies within the range 5.00–8.00 % for 90 sec of preconcentration time. Copper, cadmium and lead were determined in synthetic as well as in natural samples by anodic stripping voltammetry (ASV).
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Voltammetric determination of titanium, vanadium, and molybdenum using a carbon paste electrode modified with cetyltrimethylammonium bromide
    (Univerzita Pardubice, 1997) Stadlober, Monika; Kalcher, Kurt; Raber, Georg
    Methods for the voltammetric determination of titanium, vanadium, and molybdenum using a carbon paste electrode modified in situ with cetyltrimethylammonium bromide (CTAB) are described. Titanium and vanadium are preconcentrated at the electrode surface via their anionic oxalate complexes from acidic solution at −1.2 and −0.9 V vs. the saturated calomel electrode. The accumulation process is due to in situ formation of an ion-exchanger at the electrode surface by adsorption of the surfactant, and to formation of ion-pairs or micellar congregates, since the concentration of CTAB is higher than the critical micellar concentration (CMC). Simultaneously during accumulation, titanium(IV)- and vanadium(V)-oxalates are reduced to their tri- and tetravalent states. The preconcentration of molybdenum(VI) was performed by adsorption and of ion-pairs of cetyltrimethylammonium and Mo(VI)-oxalates at a potential of −0.4 V. Molybdenum(VI)-oxalate is reduced to a mixed-valence compound of Mo(VI) and (V). Linear dependence of current on concentration exists in the ranges of 10 to 250 µg l−1 for titanium, 5 to 200 µg l−1 for vanadium, and 5 to 500 µg l−1 for molybdenum, when applying a preconcentration time of 1 min. The limit of detection (calculated as 3σ) is 0.1 µg l−1 Ti, 0.07 µg l−1 V, and 0.04 µg l−1 Mo with a deposition time of 10 min. The method presented in this report shows that CTAB is a suitable agent for modification of CPEs giving good reproducibility of results.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Voltammetric determination of ascorbic acid in foodstuffs using modified carbon paste electrodes
    (1997) Nováková, Marcela; Kalcher, Kurt; Schachl, Klemens; Komersová, Alena; Bartoš, Martin; Vytřas, Karel
    Application of differential pulse cathodic stripping voltammetry for determination of ascorbic acid in foodstuffs have been investigated using a carbon paste electrode modified by cobalt(II) phthalocyanine, which was found to facilitate its oxidation and to decrease the necessary overvoltage. The method showed a good linearity up to 70 ppm of ascorbic acid with a detection limit of 0.8 ppm. When applied to analyse the real samples (fruit juices), the results agreed well with those obtained by traditional titrimetric determination.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    Study of conditions for voltammetric determinations of iodine at carbon paste electrodes
    (Univerzita Pardubice, 1997) Konvalina, Jiří; Švancara, Ivan; Vytřas, Karel
    A method has been developed for the determination of iodine in the form of iodide at a carbon paste electrode (CPE) with tricresyl phosphate as a pasting liquid using differential pulse cathodic stripping voltammetry. The determination is based on the combined preconcentration mechanism of iodide anions from acidic media, probably forming ion-pairs with protonated molecules of a pasting liquid, then oxidizing to iodine at +0.7 V (vs. Ag/AgCl) and extracting onto a CPE. The detection limit of 30 µg l−1 was obtained. The procedure was successfully applied to analyse real samples of mineral water and table salts containing either iodide or iodate. The results were verified by means of reference methods, e.g. ICP-MS technique, recovery determinations and iodometric titrations.
  • Náhled
    ČlánekOtevřený přístuppeer-reviewedpublished
    New voltammetric methods for the determination of heavy metals using a montmorillonite modified carbon paste electrode
    (Univerzita Pardubice, 1997) Raber, Georg; Kalcher, Kurt; Stadlober, Monika
    A carbon paste electrode modified with the clay mineral montmorillonite (MM) has been used to develop methods for the voltammetric determinations of cadmium(II), lead(II), copper(II) and mercury(II). The CPE has been modified by a newly developed procedure by direct mixing of the clay mineral, swollen in 1M KCl solutions for 12 hours and dried at 100 °C with the carbon paste. The analytical methods are based on the ion exchange properties of montmorillonite (MM). Methodological parameters such as pH of the analyte solution, preconcentration time and dependence of the voltammetric signal on the concentration of the analyte are investigated; the influence of interferents is studied. The detection limits (3σ) are 160 ng l−1 for cadmium, 600 ng l−1 for lead, 430 ng l−1 for copper and 10 ng l−1 for mercury(II) applying a preconcentration time of 10 minutes. To show the applicability of the methods, environmental samples are investigated. Another topic of the work presented here is to model preconcentration of divalent cations under open circuit conditions. The applicability of a model described by Kalcher et al. is investigated with all ionic species in question. The results show that the congruence between experimental and modelled data is excellent. A comparison of equilibrium constants obtained from electrochemical experiments and calculated by the model and equilibrium constants obtained from batch experiments shows almost excellent correlation.