Národní úložiště šedé literatury Nalezeno 52 záznamů.  předchozí11 - 20dalšíkonec  přejít na záznam: Hledání trvalo 0.00 vteřin. 
Silver Solid Amalgam Electrodes as Perspective Tools for Sensitive Voltammetric Determinations of Food Azo Dyes Amaranth and Allura Red AC
Tvorynska, S. ; Barek, J. ; Josypčuk, Bohdan
In this paper, for the first time, the electrochemical behaviours of the food azo dyes Amaranth (E 123) and Allura Red AC (E 129) were investigated on two modifications of silver solid amalgam electrode, namely mercury meniscus modified, polished and compared with hanging mercury drop electrode using differential pulse voltammetry and direct current voltammetry. The effect of adsorption and the reduction mechanism on tested electrodes were described in detail. Measurements with amalgam electrodes showed good reproducibility, stability and high sensitivity. As a result, they were successfully applied for the determination of investigated azo dyes in different commercial drink samples.
Chování metalothieneinů a fytochelatinů na rtuťových a amalgámových elektrodách
Šestáková, Ivana ; Navrátil, Tomáš ; Josypčuk, Bohdan
Při použití elektrod AgSAE či CuSAE pro elektrochemická měření s metalothioneiny či fytochelatiny vznikají příslušné Ag-MT, Cu-MT, Ag-PC či Cu-PC komplexy. V čistých elektrolytech a pro nízké koncentrace analytů jsou odezvy lineárně závislé na jejich koncentraci, odezvu je možné zvýšit akumulací při vhodném potenciálu. Pro reálné vzorky je podstatný negativní vliv matrice, který může vést až k nutnosti přípravy nového povrchu a jeho aktivace pro každý jednotlivý záznam.
Electrochemical Measurements in Flow Systems on Silver Amalgam Tubular Detector Combined with Auxiliary Electrode
Josypčuk, Bohdan ; Barek, J. ; Josypčuk, Oksana
A new type of tubular detector (TD+AuxE) was proposed, fabricated, tested and compared\nwith a typical silver amalgam tubular detector developed earlier. Non-stop-flow differential\npulse voltammetric anodic stripping method (AS-DPV) and amperometric method in a\nglucose oxidase biosensor arrangement were tested. Both detectors were applied for AS-DPV\nmeasurements in flow systems for the first time. The proposed combination of tubular\ndetector with auxiliary electrode provides a much greater current response than the classic\narrangement with three individual electrodes. All relevant parameters (potentials of\naccumulation or detection, flow rate, analyte concentrations, shielding sleeve length, etc.)\nwere optimized for the developed TD+AuxE.
Electrochemical biosensors with flow-through enzymatic reactors
Josypčuk, Oksana ; Josypčuk, Bohdan
Twelve enzymatic biosensors with various silica powder reactors were fabricated and tested.\nExperiments with six silica materials showed that mesoporous silica SBA-15 was the best one\nin terms of covering by enzymes, sensitivity and lifetime of biosensors. The current response\nof the SBA15-glucose oxidase (GOx) sensor started to decrease only after 200-day testing.\nThe used amalgam tubular detector in a flow system allowed working at highly negative\npotentials. Statistical results of parallel measurements of model solutions with the fabricated\nbiosensors show their high accuracy and sensitivity. The proposed SBA15-GOx biosensor\nwas used for determination of glucose in commercial honey.
Voltammetry of Metallothioneins on Mercury Meniscus Modified Silver Solid Amalgam Electrode
Šestáková, Ivana ; Křivská, D. ; Josypčuk, Bohdan ; Nováková, Kateřina ; Navrátil, Tomáš
Peak of AgMT is formed on m-AgSAE from MT in alkaline media. The height of this peak is proportional to the MT concentration in range 37- to 301 ng /ml and can be increased with accumulation. In ammonia solution with Co(III) salt, apart from usual Brdička response at -1400 mV another, more positive catalytic system is observed, when formation of AgMT is allowed. This phenomenon has been confirmed by elimination voltammetry.
Electrochemical Biosensors Based on Silver Solid Amalgam for Analysis in Flow Systems
Josypčuk, Oksana ; Barek, J. ; Josypčuk, Bohdan
In this contribution, the construction and preparation of 3 types of flow amperometric enzymatic biosensors based on silver solid amalgam (AgSA) were presented. Two of them consist of the tubular detector and enzymatic reactor of porous or powdered AgSA. The third biosensor was constructed using polished AgSA electrode. Reactors and polished AgSA electrodes were modified with thiols or chitosan and different enzymes were covalently immobilized by suitable techniques. Prepared biosensors were used for determination of ascorbic acid, glucose, hydrogen peroxide, catechol, pyrogallol, dopamine and sarcosine in model samples and in same cases in the real samples.
Unique Properties of Amalgam Electrodes
Josypčuk, Bohdan ; Josypčuk, Oksana
Depending on metal-mercury ratio and on the method of preparation amalgam can be: 1) solid compact; 2) paste; 3) liquid; 4) monocrystalline; 5) porous; 6) powdered. High potential of hydrogen overvoltage is observed on amalgam electrodes and it is comparable with one on Hg-electrodes. Another important benefit is the possibility to prepare amalgam electrode, detector or reactor of required size and shape. From amalgams have been prepared and tested many types of electrodes for batch and flow-through systems. The diversity of amalgam materials provides some unique electrochemical properties of electrodes, the most important of which are described in this paper.
Transport of Phytochelatin PC2 across Model Phospholipid Membrane
Šestáková, Ivana ; Nováková, Kateřina ; Josypčuk, Bohdan ; Navrátil, Tomáš
Using electrochemical cell with two compartments separated by phospholipid membrane on polycarbonate support, transport of phytochelatin PC2 by means of cell penetrating peptide TP10 and in lesser extent with Mastoparan X was confirmed with voltammetry. Formation of the membrane and transport was followed by electrochemical impedance spectroscopy.
Electrochemical Biosensors Based on Enzymatic Reactor with Amalgam Powder
Josypčuk, Bohdan ; Barek, J. ; Josypčuk, Oksana
Enzymatic reactor based on the powder of silver solid amalgam was suggested as the main part of biosensors in flow systems for the first time. 4-aminothiophenol, glutaraldehyde and enzyme were gradually bonded to the amalgam surface. Large surface of the fine amalgam particles maintains a big quantity of enzyme molecules. Biosensors were tested with enzymes ascorbate oxidase, glucose oxidase, catalase, tyrosinase and laccase. Electrochemical detection of the oxygen concentration change (for the first 3 enzymes) or the quinones concentration (tyrosinase and laccase) in the measured solution was done amperometrically by means of the tubular detector of silver solid amalgam. The current response of each biosensor was optimized with respect to the detection potential, the flow rate of the mobile phase, the injection volume and the enzymatic reactor volume. Under the found optimum conditions, concentration dependence and some statistical parameters of repeated measurements (relative standard deviation (RSD) for the studied enzymes was in the range 0.81 – 2.1 %) were measured. Biosensor with the ascorbate oxidase reactor was used for determination of ascorbic acid in the vitamin tablet Celaskon®. Results of the analysis were in good agreement with the contents of ascorbic acid declared by manufacturer and the RSD of these analyses was 2.0 %.
Construction and Application of Tubular Detector and Porous Flow-through Detector/Reactor of Silver Solid Amalgam for Electrochemical Measurements in Flow Systems
Josypčuk, Oksana ; Barek, J. ; Josypčuk, Bohdan
This paper presents the preparation and application of two new arrangements of silver solid amalgam (AgSA) electrodes for measurements in flow systems  tubular detector based on compact AgSA, and flow-through detector (or reactor) prepared from porous AgSA. Both electrodes were tested for electrochemical determinations of reducible inorganic (Cd2+, Zn2+) and organic (4-nitrophenol, lomustine) compounds under FIA with amperometric detection (Cd2+, Zn2+, 4-nitrophenol) and flow-DPV (lomustine). Furthermore, by combination of the porous reactor with immobilized enzyme and tubular detector the flow amperometric enzymatic biosensor was constructed for determination of glucose in a sample of honey and cholesterol and sarcosine in model samples.

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