Carbon paste electrodes in electroanalytical chemistry

An overview is given dealing with the applications of carbon paste electrodes in equilibrium potentiometry as well as in electrochemical stripping analysis using both voltammetric and potentiometric modes. Various modifications of carbon pastes and carbon paste-based biosensors are also mentioned. The main emphasis in this article is directed at summarizing recent results of the authors’ research group during the past few years

Screen-Printed Carbon Electrodes Modified by Rhodium Dioxide and Glucose Dehydrogenase

The described glucose biosensor is based on a screen-printed carbon electrode (SPCE) modified by rhodium dioxide, which functions as a mediator. The electrode is further modified by the enzyme glucose dehydrogenase, which is immobilized on the electrode's surface through electropolymerization with m-phenylenediamine. The enzyme biosensor was optimized and tested in model glucose samples. The biosensor showed a linear range of 500–5000 mg L−1 of glucose with a detection limit of 210 mg L−1 (established as 3σ) and response time of 39 s. When compared with similar glucose biosensors based on glucose oxidase, the main advantage is that neither ascorbic and uric acids nor paracetamol interfere measurements with this biosensor at selected potentials

Voltammetric determination of cholecalciferol at glassy carbon electrode performed in water ethanol mixture

To confirm or disprove previous hypotheses, cyclic voltammetry of 0.5 mM cholecalciferol (vitamin D3) at glassy carbon electrode (GCE) and platinum disk electrode (PtE) in pure acetonitrile and water‑ethanol mixture at 50 mV·s‑1 has been used to investigate the oxidation mechanism. The oxidation occurs in two one-electrone steps. According to calculation of the highest electron density in cholecalciferol molecule which is evidently delocalized over carbon atoms of the three conjugated double bonds (C19, C10, C5-C8) points to part of the molecule involved in oxidation processes. An oxidation peak (at +0.925 V vs. Ag/AgCl) was used to develop direct voltammetric method based on differential pulse voltammetry for the vitamin D3 determination at GCE performed in 40% ethanol containing 0.1 M LiClO4. Under optimization of analytical procedure, it was found that a composition of the supporting electrolyte used significantly affects a current response of oxidation peak obtained. Satisfactory sensitivity was achieved in the 1:1 water‑ethanol mixture containing 0.05 M lithium perchlorate as as supporting electrolyte. The linear range for vitamin D3 determination was2.4 × 10-6 - 3.5 × 10-4 M with the detection limit of 8.0 × 10-7 M. This work demonstrates a fact that the GCE is suitable electroanalytical device for analysis of various food supplements and medicaments

Voltammetric Determination of the Herbicide Linuron Using a Tricresyl Phosphate-Based Carbon Paste Electrode

This paper summarises the results of voltammetric studies on the herbicide 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (Linuron), using a carbon paste electrode containing tricresyl phosphate (TCP-CPE) as liquid binder. The principal experimental conditions, such as the pH effect, investigated in Britton-Robinson buffer solutions (pH 2.0–7.0), the peak characteristics for the analyte of interest, or instrumental parameters for the differential pulse voltammetric mode were optimized for the method. As found out, the best electroanalytical performance of the TCP-CPE was achieved at pH 2.0, whereby the oxidation peak of Linuron appeared at ca. +1.3 V vs. SCE. The analytical procedure developed offers good linearity in the concentration range of 1.25–44.20 μg mL−1 (1.77 × 10−4–5.05 × 10−6 mol L−1), showing—for the first time—the applicability of the TCP-CPE for anodic oxidations in direct voltammetry (without accumulation). The method was then verified by determining Linuron in a spiked river water sample and a commercial formulation and the results obtained agreed well with those obtained by the reference HPLC/UV determination

The voltammetric behaviour of lead at a hand drawn pencil electrode and its trace determination in water by stripping voltammetry

This is the first reported the proof of concept application of pencil drawn electrodes (PDEs) for anodic stripping voltammetric determination of Pb2+ or any metal ion. PDEs offer advantages of economics, simplicity and rapid fabrication, affording a green alternative for the development of new devices. Cyclic voltammetric investigations of Pb2+ at these electrodes in 0.30 M acetic acid were characterised by a cathodic reduction peak on the initial negative scan resulting from the reduction of Pb2+ ions to Pb0. Anodic peaks obtained on the return positive scan showed that Pb had been deposited as a thin film on the PDE surface. The addition of Cl ions to this electrolyte improved the voltammetric behaviour and a supporting electrolyte of 0.30 M acetic acid containing 0.25 M KCl was found to be optimum. Investigations were made into the possibility of determining trace levels of Pb2+ by differential pulse anodic stripping voltammetry. The effect of accumulation potential and time were investigated and optimised. Three anodic stripping peaks were recorded resulting from the heterogeneous nature of the electrode surface. Using an accumulation potential of 1.1 V and an accumulation time of 200 s a bimodal calibration curve was recorded, with linear ranges between 80 to 330 ng/mL and 330 to 915 ng/mL. The theoretical detection limit (3σ) was calculated as 9.5 ng/mL. Pb2+ determinations on a drainage water sample gave a mean recovery of 100.9 % (%CV= 5.7 %) at a concentration of 166.1 ng/mL indicating the method holds promise for the determination of Pb2+ in such samples

Nový příspěvek kpotenciometrickým titracím aniontových tenzidů

Two novel approaches in ion-pair formationbased potentiometric titrations of anionic surfactants are presented. First, a new type of the low ohmic coated-wire ion-selective electrode is introduced; the polymeric membrane containing a plasticizer mixed with carbon powder. Second, didecyldimethylammonium chloride as the cationic titrant is for the first time proposed and applied, providing the titration curves with the highest potential jump.V článku jsou popsány možnosti potenciometrické indikace titrace aniontových tenzidů s využitím "coated-wire" iontově-selektivní elektrody