Vlastimil Vyskočil

Mercury Electrodes–Possibilities and Limitations in Environmental Electroanalysis

Recent developments in the use of polarography and voltammetry at mercury electrodes in environmental analysis are reviewed and their combination with preliminary separation and pre-concentration using liquid or solid phase extraction is discussed. Attention is focused on ecotoxic nitrated polycyclic aromatic hydrocarbons, heterocyclic compounds, and pesticides. Advantages and limitations of mercury electrodes are critically evaluated and some recent applications of these techniques developed in our laboratory are given.

Adsorptive Stripping Voltammetry of Environmental Carcinogens

This review describes our recent results regarding adsorptive stripping voltammetric determination of submi- cromolar and nanomolar concentrations of various environmentally important chemical carcinogens using both traditional (hanging mercury drop electrode, carbon paste electrode) and non-traditional types of electrodes (solid amalgam elec- trodes, glassy carbon paste electrodes, carbon ink film electrodes, solid composite electrodes). The review concentrates on our own results in the context of the general development in the filed.

Voltammetric Determination of Carcinogenic Derivatives of Pyrene Using a Boron-Doped Diamond Film Electrode

Based on the study of voltammetric behavior of carcinogenic 1-nitropyrene (1-NP), 1-aminopyrene (1-AP), and 1-hydroxypyrene (1-HP), optimum conditions have been found for the determination of these analytes by differential pulse voltammetry (DPV) at a boron-doped diamond film electrode. The optimum medium was methanol-Britton–Robinson buffer (BR buffer) pH 3.0 (70:30) for 1-NP and 1-AP, and methanol-BR buffer pH 5.0 (70:30) for 1-HP. Concentration dependences of the DPV response were measured in the range 1 · 10−6–1 · 10−4 mol dm−3 (R = −0.9998) with the limit of detection (LOD) 3 · 10−7 mol dm−3 for 1-NP, 1 · 10−7–1 · 10−5 mol dm−3 (R = 0.9971) with LOD 6 · 10−8 mol dm−3 for 1-AP, and 1 · 10−7–1 · 10−5 mol dm−3 (R = 0.9934) with LOD 1 · 10−7 mol dm−3 for 1-HP. Simultaneous determination of 1-NP and 1-AP in a mixture was tested in the methanol-BR buffer pH 3.0 (70:30) medium as well. The content of 1-AP in the concentration range from 1 · 10−6 to 1 · 10−4 mol dm−3 had no effect on the sensitivity of the determination of 1-NP, and vice versa. Due to the close peak potentials of 1-AP and 1-HP, the direct determination of their mixture using voltammetric methods is impossible.

The Use of Silver Solid Amalgam Electrodes for Voltammetric and Amperometric Determination of Nitrated Polyaromatic Compounds Used as Markers of Incomplete Combustion

Genotoxic nitrated polycyclic aromatic hydrocarbons (NPAHs) are formed during incomplete combustion processes by reaction of polycyclic aromatic hydrocarbons (PAHs) with atmospheric nitrogen oxides. 1-Nitropyrene, 2-nitrofluorene, and 3-nitrofluoranthene as the dominating substances are used as markers of NPAHs formation by these processes. In the presented study, voltammetric properties and quantification of these compounds and of 5-nitroquinoline (as a representative of environmentally important genotoxic heterocyclic compounds) have been investigated using a mercury meniscus modified silver solid amalgam electrode (m-AgSAE), which represent a nontoxic alternative to traditional mercury electrodes. Linear calibration curves over three orders of magnitude and limits of determination mostly in the 10−7 mol L−1 concentration range were obtained using direct current and differential pulse voltammetry. Further, satisfactory HPLC separation of studied analytes in fifteen minutes was achieved using 0.01 mol L−1 phosphate buffer, pH 7.0 : methanol (15 : 85, v/v) mobile phase, and C18 reversed stationary phase. Limits of detection of around 1 · 10−5 mol L−1 were achieved using amperometric detection at m-AgSAE in wall-jet arrangement for all studied analytes. Practical applicability of this technique was demonstrated on the determination of 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, and 5-nitroquinoline in drinking water after their preliminary separation and preconcentration using solid phase extraction with the limits of detection around 1 · 10−6 mol L−1.

Electrochemical DNA biosensor for detection of DNA damage induced by hydroxyl radicals

A simple electrochemical DNA biosensor based on a glassy carbon electrode (GCE) was prepared by adsorbing double-stranded DNA (dsDNA) onto the GCE surface and subsequently used for the detection of dsDNA damage induced by hydroxyl radicals. Investigation of the mutual interaction between hydroxyl radicals and dsDNA was conducted using a combination of several electrochemical detection techniques: square-wave voltammetry for direct monitoring the oxidation of dsDNA bases, and cyclic voltammetry and electrochemical impedance spectroscopy as indirect electrochemical methods making use of the redox-active indicator [Fe(CN)6]4-/3-. Hydroxyl radicals were generated electrochemically on the surface of a boron-doped diamond electrode and chemically (via the Fentons reaction or the auto-oxidation of Fe(II)). The extent of dsDNA damage by electrochemically generated hydroxyl radicals depended on the current density applied to the generating electrode: by applying 5, 10, and 50mAcm-2, selected relative biosensor responses decreased after 3min incubation from 100% to 38%, 27%, and 3%, respectively. Chemically generated hydroxyl radicals caused less pronounced dsDNA damage, and their damaging activity depended on the form of Fe(II) ions: decreases to 49% (Fentons reaction; Fe(II) complexed with EDTA) and 33% (auto-oxidation of Fe(II); Fe(II) complexed with dsDNA) were observed after 10min incubation.

DNA-based biosensors with external Nafion and chitosan membranes for the evaluation of the antioxidant activity of beer, coffee, and tea

AbstractNovel electrochemical DNA-based biosensors with outer-sphere Nafion and chitosan protective membranes were prepared for the evaluation of antioxidant properties of beverages (beer, coffee, and black tea) against prooxidant hydroxyl radicals. A carbon working electrode of a screen-printed three-electrode assembly was modified using a layer-by-layer deposition technique with low molecular weight double-stranded DNA and a Nafion or chitosan film. The membrane-covered DNA biosensors were initially tested with respect to their voltammetric and impedimetric response after the incubation of the beverage and the medium exchange for the solution of the redox indicator [Fe(CN)6]3−/4−. While the Nafion-protected biosensor proved to be suitable for beer and black tea extracts, the chitosan-protected biosensor was successfully used in a coffee extract. Afterwards, the applicability was successfully verified for these biosensors for the detection of a deep degradation of the surface-attached DNA at the incubation in the cleavage agent (hydroxyl radicals generated via Fenton reaction) and for the evaluation of antioxidant properties of coffee and black tea extracts against prooxidant hydroxyl radicals. The investigation of the novel biosensors with a protective membrane represents a significant contribution to the field of electrochemical DNA biosensors utilization.

Bismuth film electrode at a silver solid amalgam substrate as a new tool for voltammetric determination of electrochemically reducible organic compounds

New type of bismuth film electrode prepared by electrodeposition of bismuth film on a silver solid amalgam substrate (BiF-AgSAE) was tested as a sensor for voltammetric determination of electrochemically reducible organic substances using 2-amino-6-nitrobenzothiazole (ANBT) as a model analyte. Using the optimized conditions (a 9:1 (v/v) mixture of aqueous Britton-Robinson buffer solution (pH 10.0) and methanol), the limits of quantification are 0.16 μmol L(-1) for direct current voltammetry (DCV) and 0.22 μmol L(-1) for differential pulse voltammetry (DPV). The obtained calibration dependences are linear in the concentration range from 0.2 to 100 μmol L(-1) and the practical applicability of the newly developed electrode for the direct determination of ANBT in tap and mineral water model samples was confirmed in the concentration range from 0.2 to 10 μmol L(-1).

Voltammetric Determination of 5-nitroindazole using a Bismuth Bulk Electrode

ABSTRACT A rapid simple fabrication method for the bismuth bulk working electrode is reported using a Pasteur pipette tip filled with molten bismuth to form a disk. The applicability of the newly developed electrode was verified by differential pulse voltammetric determination of 5-nitroindazole, which is a reagent for organic synthesis. The 5-nitroindazole shows high toxicity against parasites from the Trypanosomatidae family and it is a proven mutagen for bacterial cultures. A Britton-Robinson buffer of pH 8.0 was chosen as the optimal medium for this determination. The calibration curve was measured from 2 to 100 micromoles per liter (r = −0.9989) with limits of detection and quantification of 0.20 and 0.67 micromole per liter, respectively. The developed method was successfully applied for the analysis of drinking and river water.

Determination of Methyl Violet 2B using Polarographic and Voltammetric Methods at Mercury Electrodes

ABSTRACT Direct current tast polarography and differential pulse polarography at a dropping mercury electrode and direct current voltammetry, differential pulse voltammetry, and differential pulse adsorptive stripping voltammetry at a hanging mercury drop electrode were employed for the electrochemical characterization and determination of methyl violet 2B in buffered aqueous media and model water samples. The optimum medium for all techniques was 0.04 mole per liter Britton-Robinson buffer at pH 4.0. The limits of quantification for methyl violet 2B were 1.7 micromole per liter (direct current tast polarography at the dropping mercury electrode), 0.16 micromole per liter (differential pulse polarography at the dropping mercury electrode), 65 nanomoles per liter (direct current voltammetry at the hanging mercury drop electrode), and 45 nanomoles per liter (differential pulse voltammetry at the hanging mercury drop electrode). The lowest limit of quantification of 13 nanomoles per liter was obtained using differential pulse adsorptive stripping voltammetry at the hanging mercury drop electrode with an accumulation potential of −500 millivolts and an accumulation time of 600 seconds. The optimized conditions were employed for the determination in drinking (limit of quantification of 40 nanomoles per liter) and river (limit of quantification of 20 nanomoles per liter) water.

Voltammetric determination of trace amounts of diacetyl at a mercury meniscus modified silver solid amalgam electrode following gas-diffusion microextraction

A new approach was developed for the determination of trace amounts of diacetyl in food products using gas-diffusion microextraction (GDME) and subsequent detection by differential pulse voltammetry (DPV) at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE). Diacetyl is a vicinal diketone responsible for the buttery aroma in many fermented foods and beverages. Its determination is important not only for evaluation of the final product quality (note of mention: health related concerns were associated with continuous diacetyl exposure) but also to monitor fermentation. GDME, a technique combining gas-diffusion and microextraction, particularly aimed to volatile and semi-volatile analytes, seemed the best way to selective extract diacetyl. A solution of 0.05% o-phenylenediamine (OPDA) prepared in a Britton-Robinson buffer (pH 5.0) was chosen as the extracting solution. This solution simultaneously extracts, pre-concentrates and derivatizes diacetyl to 2,3-dimethylquinoxaline (DMQ), enhancing the extraction selectivity and making the analyte electroactive. After finding the optimum conditions for the extraction process (10min at 60°C with 1.0mL of OPDA at pH 5.0), the DPV measurements at the m-AgSAE were conducted with a scan rate of 7mVs-1, a modulation amplitude of 50mV and a modulation time of 100ms. Under these conditions, the resulting DMQ could be easily measured at a potential of -0.6V vs. Ag|AgCl (3molL-1 KCl). The amalgam electrode keeps the advantages of classic mercury electrodes, like high sensitivity, while being environmentally friendly. The GDME/m-AgSAE produced suitable method features for the determination of low amounts of diacetyl (as DMQ) in alcoholic beverages, and in fact, to the best of our knowledge, the limit of quantification of 0.18µgL-1 is one of the lowest reported in literature.