Renato Seeber

Analytical and spectroscopic characterization of humic acids extracted from sewage sludge, manure, and worm compost.

Humic acids extracted from sewage sludges, manure, and worm compost have been characterized by chemical and spec-troscopic methods. Meaningful differences in the composition were revealed by FT IR, 1H, 13C NMR, and visible spectroscopies. These differences allow a differentiation amomg the products depending on the source from which they were obtained. Humic acid extracted from sewage sludges contains the highest percentage of aliphatic carbon, associated with polysaccharides and proteinaceous structures, and has characteristics close to those of aquatic humic acids. On the other hand, humic acids from manure and worm compost are similar to the humic acids originating from soil.

Electrocatalytic properties of nickel(II) hydrotalcite-type anionic clay: application to methanol and ethanol oxidation

Abstract Glassy carbon electrodes modified with a [Ni/Al–Cl] hydrotalcite-type anionic clay have been studied with respect to the electrochemical oxidation of the Ni(II) centres. The oxidation of Ni(II) is quasi-reversible and the presence in the hydrotalcite lattice of nickel with mixed oxidation states increases the conductivity of the coverage strongly. It has been verified that these nickel redox systems may act as redox mediators for the oxidation of alcohol substrates (methanol and ethanol have been tested) which are not oxidised at the bare electrode in the potential window available. For both alcohols the height of the current responses in linear sweep voltammetry is roughly linear with varying concentration in solution up to a limit of ca. 3000 ppm, with a detection limit of 3–4 ppm.

WPTER: wavelet packet transform for efficient pattern recognition of signals

Abstract In the present work, we propose a novel algorithm based on the Wavelet Packet Transform (WPT) for pattern recognition of signals, which operates both feature selection and classification at the same time: Wavelet Packet Transform for Efficient pattern Recognition of signals (WPTER). The distinctive characteristics of WPTER with respect to the previously proposed algorithms for the WPT-based classification of signals consist mainly of two aspects: (1) a Classification Ability criterion is introduced into the procedure for selection of the best discriminant basis; (2) the signals are reconstructed in the original domain by using only the selected wavelet coefficients, which allow for chemical interpretation of the results. The algorithm was first tested on an artificial (simulated) set of signals, consisting of a number of subsequent peaks, partially overlapped to each other, with added noise and baseline drift, simulating a three-class system. Then, it was applied to a data set consisting of X-ray diffractograms on fired tiles subjected to different firing cycles, aiming at discriminating the different firing methods on the basis of the phase composition. In both cases, satisfactory classifications were achieved.

Electrochemical preparation and characterisation of bilayer films composed by Prussian Blue and conducting polymer

Abstract Preparation and electrochemical behaviour of bilayer films consisting of iron(III) hexacyanoferrate, well known as Prussian Blue, and of poly[4,4 ′ -bis(butylsulphanyl)-2,2 ′ -bithiophene], on a platinum electrode, are reported. The electrochemical features of the Prussian Blue/conducting polymer bilayer system are examined in aqueous and acetonitrile solutions. Cyclic voltammetric studies show that, in acetonitrile solvent, the inner layer Prussian Blue is electroactive to some extent, though the electrochemical response of the system is mainly accounted for by poly[4,4 ′ -bis(butylsulphanyl)-2,2 ′ -bithiophene] outer layer. On the other hand, in aqueous solution Prussian Blue exhibits good electroactivity. Under specific experimental conditions, the individual redox behaviour of each constituent of the bilayer is evidenced in the two solvents separately, i.e., that of PB and that of poly[4,4 ′ -bis(butylsulphanyl)-2,2 ′ -bithiophene] in aqueous and in organic solvent, respectively. However, interesting reciprocal influences are evident in the current/potential curves recorded under conditions which are discussed.

Electropolymerization of Tetrakis(o-aminophenyl)porphyrin and Relevant Transition Metal Complexes from Aqueous Solution. The Resulting Modified Electrodes as Potentiometric Sensors

The mechanism of electrogeneration of polyporphyrin from ortho-substituted phenylporphyrins, either free or complexing transition metals, is different when performed in aqueous solution from that operative in organic solvents, that has been reported in the literature. Polymerization occurs through the amino phenyl substituents, leading to a three dimensional ‘cage’ structure. The polymer is sensitive to morphology and nature of the surface it grows on. The mass deposited on a gold electrode was about 2 × 10–4 g/cm2. If the polymerization is performed under potentiodynamic conditions, the polymer forms essentially during the first scan, while no significant further growth is observed in subsequent potential cycles, from both free and metallated porphyrins. All polyporphyrin films, except the one obtained from CoTAPP, exhibit poor electrical conductivity, due to the three dimensional growth of the polymer chain that does not allow the necessary conjugation of π orbitals inside the macromolecules. On the other hand, interesting properties are shown by the unmetallated as well as by metallated polymer films as possible coverages for ‘coated wire’ ion selective electrodes. The results obtained with respect to different ions and, in particular, a selectivity study carried out on iodide ions are reported.

Polythiophenes and polythiophene-based composites in amperometric sensing

AbstractThis overview of polythiophene-based materials provides a critical examination of meaningful examples of applications of similar electrode materials in electroanalysis. The advantages arising from the use of polythiophene derivatives in such an applicative context is discussed by considering the organic conductive material as such, and as one of the components of hybrid materials. The rationale at the basis of the combination of two or even more individual components into a hybrid material is discussed with reference to the active electrode processes and the consequent possible improvements of the electroanalytical performance. In this respect, study cases are presented considering different analytes chosen among those that are most frequently reported within the classes of organics and inorganics. The use of a polythiophene matrix to stably fix biological elements at the electrode surface for the development of catalytic biosensors and genosensors is also discussed. Finally, a few possible lines along which the next research in the field could be fruitfully pursued are outlined. Furthermore, the work still to be done to exploit the possibilities offered by novel products of organic synthesis, even along paths already traced in other fields of electrochemistry, is discussed. Prototypical voltammetric responses obtained in a solution of two analytes on: bare electrode (left); polythiophine-based coated electrode (right).

Oxidation potentials of electrolyte solutions for lithium cells

Abstract The oxidation potentials, E ox , of several solutions of interest for nonaqueous Li cells have been measured by linear sweep voltammetric experiments. A correlation is found between E ox and the basicity of the solvents, expressed by their donor numbers (DN). Esters and sulfones have higher resistance to oxidation than ethers, which possess the highest DN values. All solutions have E ox > 4 V vs Li/Li + . However, some reactivity between positive electrodes and solutions has been observed below this potential.

Polythiophene Derivative Conducting Polymer Modified Electrodes and Microelectrodes for Determination of Ascorbic Acid. Effect of Possible Interferents

Conventional-size electrodes and microelectrodes coated by electrogenerated poly[4,4′-bis(butylsulfanyl)-2,2′-bithiophene] have been tested with respect to the electrocatalytic oxidation of a particularly interesting analyte, i.e., ascorbic acid, in different concentrations of phosphate buffer, aqueous solution. Linear sweep and cyclic voltammetry have been used and the quantities related to the analyte concentration were the peak current and the diffusion (t−1/2) deconvoluted peak current in the case of conventional-size and of microelectrode, respectively. Fairly good linear correlation could be found; a particularly wide linearity range was obtained by working with the microelectrode. It showed to give good results also at a very low (10−4 M) phosphate buffer-supporting electrolyte concentration. The actual interference on the analysis of compounds often coupled with ascorbic acid in natural or pharmaceutical products has been studied.

Development of Quantitative Structure−Property Relationships Using Calculated Descriptors for the Prediction of the Physicochemical Properties (nD, ρ, bp, ε, η) of a Series of Organic Solvents

Quantitative structure−property relationship (QSPR) models were derived for predicting boiling point (at 760 mmHg), density (at 25 °C), viscosity (at 25 °C), static dielectric constant (at 25 °C), and refractive index (at 20 °C) of a series of pure organic solvents of structural formula X−CH2CH2−Y. A very large number of calculated molecular descriptors were derived by quantum chemical methods, molecular topology, and molecular geometry by using the CODESSA software package. A comparative analysis of the multiple linear regression techniques (heuristic and best multilinear regression) implemented in CODESSA, with the multivariate PLS/GOLPE method, has been carried out. The performance of the different regression models has been evaluated by the standard deviation of prediction errors, calculated for the compounds of both the training set (internal validation) and the test set (external validation). Satisfactory QSPR models, from both predictive and interpretative point of views, have been obtained for all...

Amperometric sensors based on poly (3,4-ethylenedioxythiophene)-modified electrodes: Discrimination of white wines

The voltammetric responses on selected white wines of different vintages and origins have been systematically collected by three different modified electrodes, in order to check their effectiveness in performing blind analysis of similar matrices. The electrode modifiers consist of a conducting polymer, namely poly(3,4-ethylenedioxythiophene) (PEDOT) and of composite materials of Au and Pt nanoparticles embedded in a PEDOT layer. Wine samples have been tested, without any prior treatments, with differential pulse voltammetry technique. The subsequent chemometric analysis has been carried out both separately on the signals of each sensor, and on the signals of two or even three sensors as a unique set of data, in order to check the possible complementarity of the information brought by the different electrodes. After a preliminary inspection by principal component analysis, classification models have been built and validated by partial least squares-discriminant analysis. The discriminant capability has been evaluated in terms of sensitivity and specificity of classification; in all cases quite good results have been obtained.