Aleksander Ciszewski

Electrocatalytic oxidation of alcohols on glassy carbon electrodes electrochemically modified by conductive polymeric nickel(II) tetrakis(3-methoxy-4-hydroxyphenyl) porphyrin film

The electrocatalytic oxidation of methanol and other simple alcohols in alkaline solution at a nickel-based chemically modified glassy carbon electrode was investigated. As a modifier a conductive polymeric nickel(II) tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin film was used. The modified electrode was characterized by cyclic voltammetry, and its analytical utility was checked by using batch injection analysis.

Electrochemical detection of nitric oxide using polymer modified electrodes

Electrochemical sensors based on chemical surface modification are very attractive because they combine high sensitivity of amperometry with new dimensions of selectivity and stability provided by the surface modifier. This review shows a few strategies employed to facilitate the detection, determination and monitoring of nitric oxide using polymer modified electrodes. Conducting and nonconducting polymer films and composite films are considered. The most significant achievements reached in this field, during the last decade, are critically reviewed. The collected data are also presented in three tables.

Glassy carbon electrode modified by conductive, polymeric nickel(II) porphyrin complex as a 3D homogeneous catalytic system for methanol oxidation in basic media

Abstract The voltammetric behaviour in alkaline solution of a nickel-based chemically modified electrode (poly-NiTMHPP) prepared by oxidative electropolymerization of a nickel tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin for electro-oxidation of methanol was investigated by cyclic voltammetry and the rotating disk technique. The oxidation of methanol occurs at 0.61 V vs. SCE, where oxidation is not observed at the bare electrode. The dependence of the oxidation current on the methanol concentration and on the number of redox centres Ni(II)/Ni(III) is discussed. From the fact that the oxidation current increases with increasing film thickness it is evident that the electrocatalytic reaction occurs inside the polymer film. The system examined is a typical example of a redox polymer with 3D properties. It is also concluded that the reaction mechanism of methanol electro-oxidation is of the so-called “R” case, according to the concept of Saveant and Andrieux, i.e. a cross-exchange reaction is the limiting step.

Kinetics of electrocatalytic oxidation of formaldehyde on a nickel porphyrin-based glassy carbon electrode

Abstract Electrocatalytic oxidation of formaldehyde on a glassy carbon modified with electropolymerised films derived from tetrakis(4-hydroxy-3-methoxyphenyl)porphinato nickel(II) (THMPPNi(II)) was studied in 0.1 M NaOH on stationary and rotating electrodes by cyclic voltammetry and rotating disc amperometry, respectively. The data from rotating disc experiments were analysed according to Albery–Hillman theory. The findings showed that the poly-THMPPNi(II) behaves as an efficient electrocacalyst for the oxidation of formaldehyde with the cross-exchange reaction occurring throughout the layer at a low concentration of formaldehyde and for a thin modifier, i.e. the mediating process corresponds to the Lk kinetic case, with a change over to the LEk regime at higher substrate concentration or for thicker films.

A New Nafion‐Free Bipolymeric Sensor for Selective and Sensitive Detection of Nitric Oxide

An amperometric/voltammetric sensor for the determination of nitric oxide based on its oxidation on a glassy carbon (GC) electrode modified by polymerized nickel(II) tetrakis(4-hydroxy-3-methoxyphenyl)porphyrin (NiTHMPP) and additionally covered by polymerized eugenol (4-allyl-2-methoxyphenol) (PE) is described. Cyclic voltammetry was used to compare the performance of Nafion and PE as selective membranes for NO sensors. Our findings showed that the electrodes with PE can be successfully applied to NO detection either by DPV (oxidation peak appeared at +0.75 V vs. Ag/AgCl) or by amperommetry at +0.8 V. The electrodes were very sensitive to NO, with detection limit of 85 nM (S/N = 3), and at the same time were also very selective against ureate (> 104:1), ascorbate (> 5 × 103:1) and nitrite (>103:1). Moreover, PE coated electrodes, comparing with those with Nafion, displayed significantly better selectivity against positively charged species: dopamine (ca. 80:1) and epinephrine (ca. 150:1).

Preparation and General Properties of Chemically Modified Electrodes Based on Electrosynthesized Thin Polymeric Films Derived from Eugenol

Eugenol (4-allyl-2-methoxyphenol) was polymerized oxidatively by cyclic voltammetry at platinum and glassy carbon electrodes. It was found that at platinum the polymerization gives rise to a uniform, compact film which could serve as a permselective membrane for analytes of small molecular size. Applications of such films in selective detection of hydrogen peroxide and nitric monoxide were proposed. Monomer oxidation at glassy carbon resulted in less compact films. Interestingly, at higher potentials a porous structure containing large amount of unoxidized o-methoxyphenyl groups was created. This structure underwent electrochemical demethoxylation leading to the generation of redox active o-quinone functionalities when the modified electrode was cycled in acidic solution. A small amount of p- quinone functionalities was also generated. As could be anticipated the redox couples were capable of mediating electrochemical oxidation of ascorbic acid and NADH. Additionally polymeric eugenol-coated GC exhibited preconcentration capabilities towards dissolved metal cations. This effect was demonstrated on the electrochemical oxidation of preconcentrated Ce(III) and reduction of Cu(II).

Determination of thallium and lead in cadmium salts by anodic stripping voltammetry with addition of surfactants to suppress the cadmium peaks

Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at -0.74 V vs. SCE, in 0.1M EDTA solution: 10(-1)M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10(-2)M and 10(-5)M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between -0.50 and -0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium.

Hair analysis. Part 1: Differential pulse anodic stripping voltammetric determination of lead, cadmium, zinc and copper in human hair samples of persons in permanent contact with a polluted workplace environment

Prior to determination of Pb, Cd, Zn and Cu by differential pulse anodic stripping voltammetry microwave digestion has been evaluated for the decomposition of human hair samples using a HNO3H2O2 mixture. The efficiency of the decomposition, and the accuracy and precision of the proposed procedure was studied using a human hair standard. Hair samples were collected from the vertex of the scalps of donors who were employed in factories manufacturing lead-acid batteries, nickel-cadmium batteries and gas (petroleum) vending station workers. The results show that, in all cases, permanent contact with the polluted environment makes it possible to absorb very large amounts of lead or cadmium, simultaneously depressing zinc absorption. Results of a study on the content of the above elements in human hair of persons who had had no work place contact with these elements are also presented.

Hair analysis. Part 2. Differential pulse anodic stripping voltammetric determination of thallium in human hair samples of persons in permanent contact with lead in their workplace

Abstract The determination of thallium in human hair samples by differential pulse anodic stripping voltammetry after microwave digestion has been presented. Hair samples were collected from the vertex of the scalps of donors who were employed in factories manufacturing lead-acid batteries. The results show that permanent contact with an environment polluted by lead makes it possible to absorb very large amounts of thallium, which is present in this environment only as an impurity of lead. The study also shows that absorption of thallium by workers is a few times ‘better’ than that of lead.

Oxidation of Nitric Oxide at a Porphyrinic-Based SensorNew Results from Rotating Disk Experiments

An amperometric sensor for the determination of nitric oxide based on its oxidation on a glassy carbon electrode modified with electropolymerized vanillin porphyrin [tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin] film and Nafion is described. Our results show that the anodic oxidation of NO at the modified electrode is the result of a catalytic effect induced by the porphyrinic modifier, that acts as a 3D system. The effect of film thickness of both porphyrinic modifier and Nafion on the NO response is tested. The results of rotating disk electrode experiments are presented and a general mathematical model of the working sensor is also given.