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This study aimed to remove carbamazepine from aqueous solutions, using functional silica phenylamine (SiBN), which is characterized and showed excellent chemical and thermal stability. Adsorbents based on silica were developed due to their unusually large surface area, homogenous pore structure, and well-modified surface properties, as silica sparked tremendous interest. It was determined to develop a novel silica adsorbent including phenylamine and amide (SiBCON). The adsorbents obtained were analyzed by various spectroscopy devices, including SEM, FT-IR and TGA analysis. The maximum removal rates for carbamazepine were 98.37% and 98.22% for SiBN and SiBCON, respectively, when optimized at room temperature, pH 9.0, initial concentration of 10 mg·L−1 and contact time of 15 min. Theoretical tools are widely used in the prediction of the power of interactions between chemical systems. The computed data showed that new amine modified silica is quite effective in terms of the removal of carbamazepine from aqueous solution. Calculation binding energies and DFT data showed that there is a powerful interaction between amine-modified silica and carbamazepine.

[EN] The concrete electrical resistivity is a prominent parameter in structural health monitoring, since, along with corrosion potential, it provides relevant qualitative diagnosis of the reinforcement corrosion. This study proposes a simple expression to reliable determine resistivity from the concrete electrical resistance (R-E) provided by the corrosion sensor of the Integrated Network of Sensors for Smart Corrosion Monitoring (INESSCOM) we have developed. The novelty here is that distinct from common resistivity sensors, the cell constants obtained by the proposed expression are intended to be valid for any sensor implementation scenario. This was ensured by studying most significant geometrical features of the sensor in a wide set of calibration solutions. This embedded-sensor approach is intended to be applicable for R-E measurements obtained both using potential step voltammetry (PSV, used in the INESSCOM sensor for corrosion rate measurement) and alternating current methods. In this regard, we present a simple protocol to reliably determine R-E, and therefore resistivity, from PSV measurements. It consists in adding a very short potentiostatic pulse to the original technique. In this way, we are able to easy monitor resistivity along with corrosion rate through a single sensor, an advantage which is not usual in structural health monitoring., This research was funded by the pre-doctoral scholarship granted to Jose Enrique Ramon Zamora by the Spanish Ministry of Science and Innovation, grant number FPU13/00911. Funding was also provided by the Spanish Ministry of Economy and Competitiveness under the national program for research, development and innovation geared to societal challenges; project number BIA2016-78460-C3-3-R. The research activity reported in this paper has been partially possible thanks to the project Voltammetric Electronic Tongue for Durability Control in Concrete funded by the Universitat Politecnica de Valencia, project number SP20180245.

A binary system composed of carbon dots (CDs) and N-doped CDs (N-CDs) embedded in an organic matrix was used for the analysis of cholesterol by MALDI (matrix-assisted laser desorption and ionization time-of-flight) mass spectrometry, as a model for detection of small, biologically relevant molecules. The results showed that both CDs are sensitive to the cholesterol and can be used either alone or in a binary system with 2,5-dihydroxybenzoic acid (DHB) to enhance the detection process. It was found that both COOH and NH2 groups on CDs surface contributed to the enhancement in the cholesterol detection by MALDI mass spectrometry in the presence of inorganic cations. Nevertheless, in the presence of NaCl, N-CDs led to a better reproducibility of results. It was due to the coexistence of positive and negative charge on N-CDs surface that led to a homogeneous analyte/substrate distribution, which is an important detection parameter. The enhancing effect of carbon dots was linked to a negative Gibbs energy of the complex formation between CDs, Na+, cholesterol and DHB, and it was supported by theoretical calculations. Moreover, upon the addition of CDs/N-CDs, such features as a low ionization potential, vertical excitation, dipole moment and oscillator strength positively affected the cholesterol detection by MALDI in the presence of Na+. © 2021 Elsevier Inc. This is accepted peer-reviewed version of the article: Houdová, D., Soto, J., Castro, R., Rodrigues, J., Pino-González, M. S., Petković, M., ... & Algarra, M. (2021). Chemically heterogeneous carbon dots enhanced cholesterol detection by MALDI TOF mass spectrometry. Journal of Colloid and Interface Science, 591, 373-383. DOI:[http://dx.doi.org/10.1016/j.jcis.2021.02.004]

We studied the possibility of detection of [Ru(η5-C5H5)(PPh3)2Cl] (abbreviated by RuCp) complex as a model system for Ru-based metallodrugs in human urine by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) without previous purification or removal of inorganic salts. Inorganic salts might prevent the detection of RuCp by MALDI-TOF MS, most likely through the increased number and intensity of background/organic matrix signals. This problem might be overcome by the acquisition of matrix-free spectra and the addition of nanoparticles, such as carbon dots, to the urine solution. Our results suggest that RuCp is easily detectable by MALDI-TOF MS in all acquisition conditions, with the CHCA matrix being the best for acquisition in phosphate-containing solutions, whereas in urine, DHB and matrix-free approach demonstrated the highest sensitivity, precision, and reproducibility. The sensitivity of matrix-free MALDI detection of RuCp could be increased by the addition of carbon dots to the urine. Based on theoretical calculations for all matrix/analyte combinations, the model for the interaction of RuCp with carbon dots was established, and higher sensitivity explained.

Electrochemical surface-enhanced Raman scattering (SERS) of the cruciform system 1,4-bis((E)-2-(yridine-4-yl)vinyl)naphthalene (bpyvn) was recorded on nanostructured silver surfaces at different electrode potentials by using excitation laser lines of 785 and 514.5 nm. SERS relative intensities were analyzed on the basis of the resonance Raman vibronic theory with the help of DFT calculations. The comparison between the experimental and the computed resonance Raman spectra calculated for the first five electronic states of the Ag2-bpyvn surface complex model points out that the selective enhancement of the SERS band recorded at about 1600 cm&minus, 1, under 785 nm excitation, is due to a resonant Raman process involving a photoexcited metal-to-molecule charge transfer state of the complex, while the enhancement of the 1570 cm&minus, 1 band using 514.5 nm excitation is due to an intramolecular &pi, &rarr, &pi, * electronic transition localized in the naphthalenyl framework, resulting in a case of surface-enhanced resonance Raman spectrum (SERRS). Thus, the enhancement of the SERS bands of bpyvn is controlled by a general chemical enhancement mechanism in which different resonance processes of the overall electronic structure of the metal-molecule system are involved.

Gold nanoparticles (Au NPs) are widely used today in a broad range of applications like electronics, sensors, catalysis and especially in biomedicine. However, the increase in their use has raised concerns about the possible interactions in vivo and the unexpected responses inside humans and other living organisms. Analytical tools that are able to detect their presence in biological samples and also provide information about the presence of dissolved metal ions inside biological samples are, therefore, urgently needed for a proper understanding of the behaviour of these materials. In this work, an HPLC-ICP-MS technique for the determination of Au NPs was adapted to the analysis of tissues from Wistar rats after intraperitoneal injection of 10 nm Au NPs. This technique allows the detection of Au NPs and low-molecular Au species, permitting the detection and monitoring of potential degradation processes. Alkaline and enzymatic digestions were tested to solubilize the particles and to verify their stability during the extraction process. Enzymatic digestion with proteinase K over 14 h was found to be suitable for the extraction of the Au species with recovery rates of about 91%. Finally, the method was applied to the analysis of liver and spleen samples. Significant abundances of low-molecular Au species were detected (around 30%). This observation suggested that a degradation process played a pivotal role during the transport and accumulation of Au NPs that were intraperitoneally injected into Wistar rats.

[EN] This study was carried out to compare the results obtained using potential step voltammetry and linear sweep voltammetry with a rotating gold disc electrode (RDE), when models based on equivalent circuits (EC) were used. The results lead to an equivalent circuit model that allows us to interpret the electrochemical behavior of aqueous solutions containing Fe(CN)(6)(-4) and Fe(CN)(6)(-3). With this model, we determined the values of the electrical resistance of the medium (R-s) as well as its polarization resistance (R-p), and established correlations between these values and the kinetic parameters of the system. The proposal highlights the need to introduce a new component for modeling using EC, which we have called the electrochemical diode. (C) 2019 Elsevier Ltd. All rights reserved., The authors gratefully acknowledge the financial support of BIA2016-78460-C3-3-R, MAT2015-64139-C4-3-R and RTI2018-100910-B-C43 (MINECO/FEDER) projects. We would also like to extend our appreciation for the pre-doctoral FPU scholarships (University Teacher Training scholarship) granted to Ana Martinez Ibernon (FPU 16/00723) and Jose Enrique Ramon Zamora (FPU13/00911) by the Spanish Ministry of Science and Innovation.

Surface-enhanced Raman scattering of thiobenzoic acid and thiobenzamide have been recorded on three different silver colloids in order to find the chemical species responsible for the spectra and to detect differences in the adsorption with respect to their oxygen counterparts, benzoic acid and benzamide, respectively. Very significant and unexpected shifts of opposite sign between the Raman and SERS wavenumbers have been detected. By comparing the experimental and DFT calculated wavenumbers, it can be concluded that the acid is bonded to the metal as thiobenzoate through the sulfur atom with unidentate coordination. SERS spectra of thiobenzamide can be explained by assuming that it is adsorbed as azanion, like in the case of benzamide, linking to the metal through the sulfur and nitrogen atoms of the ionized thiocarboxamide group. In order to support these conclusions, B3LYP/LanL2DZ force field calculations for different complexes of silver cations with the thiobenzoate anion, the neutral thiobenzamide as well as its azanion have been carried out. Additionally, the 8a;?ring mode is the most enhanced band in the SERS of both adsorbates pointing to the participation of a metal-to-molecule resonant charge transfer mechanism.

This study demonstrates the feasibility of using a voltammetric electronic tongue to monitor effluent dissolved orthophosphate concentration in a struvite precipitation reactor. The electrochemical response of the electronic tongue to the presence of orthophosphate in samples collected from the effluent of the precipitation reactor is used to predict orthophosphate concentration via a statistical model based on Partial Least Squares (PLS) Regression. PLS predictions were suitable for this monitoring application in which precipitation efficiencies higher than 80% (i.e., effluent dissolved orthophosphate concentrations lower than 40 mg P-PO43- L-1) could be considered as indicator of good process performance. The electronic tongue consisted of a set of metallic (noble and non-noble) electrodes housed inside a stainless steel cylinder which was used as the body of the electronic tongue system. Fouling problems were prevented via a simple mechanical polishing of the electrodes. The measurement of each sample with the electronic tongue was done in less than 3 s. Conductivity of the samples only affected the electronic tongue marginally, being the main electrochemical response due to the orthophosphate concentration in the samples. Copper, silver, iridium and rhodium were the electrodes that exhibited noticeable response correlated with the dissolved orthophosphate concentration variations, while gold, platinum and especially cobalt and nickel were the less useful electrodes for this application. (C) 2016 Elsevier B.V. All rights reserved., Financial support from the Spanish Government (Project MAT2015-64139-C4-1), the Generalitat Valencia (Project PROME-TEOII/2014/047) is gratefully acknowledged. This research work was also possible thanks to FCC Aqualia participation in IN-NPRONTA 2011 IISIS IPT-20111023 project (partially funded by The Centre for Industrial Technological Development (CDTI) and supported by the Spanish Ministry of Economy and Competitiveness).

The effect of adsorbate concentration on the potential dependent SERS spectra of p-aminothiophenol (pATP) recorded on a silver electrode has been studied using NaClO4 as electrolyte. Multiconfigurational second-order perturbation calculations (MS-CASPT2) have been performed in order to help the analysis of the experimental results by computing resonance Raman spectra of selected structural models of the metal–adsorbate surface complex. In order to avoid as far as possible any photochemical reaction, a long wavelength exciting line of 785 nm is used in the experiments. It is found that the spectra are dependent on adsorbate concentration and dominated by a resonant charge transfer (CT) mechanism, where the charge is always transferred from the adsorbate to the metal. The relative SERS enhancements are due to Franck–Condon factors related to the CT process, and there are not intensified bands through Herzberg–Teller contributions. Furthermore, the Raman signals of the SERS recorded at low concentration aris...

Manufactured TiO2 nanoparticles (TiO2 NPs) are nowadays widely present in products accessible to the mass market like paints, cosmetics or sunscreens. Despite the great increase in the use of these nanoparticles, until now their potential effects on the environment and biological systems have not been sufficiently studied. Reliable analytical methods are therefore required for better characterization of these emerging materials. We suggest the hyphenation of inductively coupled plasma-mass spectrometry (ICP-MS) with a separation technique like sedimentation field-flow fractionation (SdFFF) to obtain information related to the size and state of agglomeration of the investigated nanoparticles. In this work, initial experiments related to the on-line coupling of SdFFF to inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) have been conducted allowing the detection and separation of TiO2 NPs. The application of the ICP-MS/MS technology using a NH3 mass shift mode allowed the removal of the different molecular and isobaric interferences that complicate the reliable detection and quantification of Ti. Under optimised conditions, the achievable instrumental detection limits in matrix solutions were below 10 ng L−1 of Ti. The separation parameters of the SdFFF system were optimized using two commercially available model TiO2 NPs (nominal sizes: 21 and 50 nm). These materials were characterised concerning hydrodynamic diameters and the state of aggregation also using a multiangle light scattering (MALS) analysis detector. A transmission electron microscopy (TEM) technique was also applied to confirm the sizes and the shapes of the TiO2 NPs as well as the presence of aggregates. To demonstrate the applicability of the combination of SdFFF and ICP-MS/MS for the detection of TiO2 NPs at trace levels as well as to gain information about their hydrodynamic diameter and agglomeration state, the optimized method has been applied to the analysis of real water samples from a local lake in Germany.

[EN] The use of a voltammetric electronic tongue for the quantitative analysis of quality parameters in influent wastewater from a wastewater treatment plant (WWTP) that treats domestic and industrial wastewater is proposed. The electronic voltammetric tongue consists of a set of four noble electrodes (iridium, rhodium, platinum and gold) housed inside a stainless steel cylinder. These noble metals have high durability and are low maintenance-demanding, as required for developing future automated equipment. A pulse voltammetry study was conducted in 35 wastewater samples to determine ammonia (NH4+-N), nitrates (NO3--N), total phosphate (tot-P), soluble chemical oxygen demand (CODs) and conductivity. These parameters were also determined in these samples by routine analytical methods in the WWTP laboratory. A partial least squares (PLS) analysis was run to obtain a model to predict each parameter. Twenty-five samples were included in the calibration set and 10 in the validation set. Calibration and validation sets were selected randomly, except for the extreme values of each parameter, which were included in the calibration set. Variable selection was performed on the voltammetric data using Genetic Algorithms in the calibration data set for each parameter. The electronic tongue showed good predictive power to determine the concentrations of NH4+-N, NO3--N and tot-P and CODs., The financial support for this work was provided by the Spanish Ministry of Economy and Competitivity though Project e-TONGUE4WAT (IPT-2012-0069-310000) IN-NPACTO and by European Union FEDER funds. Financial support from the Spanish Government (Project MAT2012-38429-C04) and the Generalitat Valencia (Project PROMETEOII/2014/047) is also gratefully acknowledged.

[EN] The use of a voltammetric electronic tongue for the quantitative analysis of quality parameters in spring water is proposed here. The electronic voltammetric tongue consisted of a set of four noble electrodes (iridium, rhodium, platinum, and gold) housed inside a stainless steel cylinder. These noble metals have a high durability and are not demanding for maintenance, features required for the development of future automated equipment. A pulse voltammetry study was conducted in 83 spring water samples to determine concentrations of nitrate (range: 6.9-115 mg/L), sulfate (32-472 mg/L), fluoride (0.08-0.26 mg/L), chloride (17-190 mg/L), and sodium (11-94 mg/L) as well as pH (7.3-7.8). These parameters were also determined by routine analytical methods in spring water samples. A partial least squares (PLS) analysis was run to obtain a model to predict these parameter. Orthogonal signal correction (OSC) was applied in the preprocessing step. Calibration (67%) and validation (33%) sets were selected randomly. The electronic tongue showed good predictive power to determine the concentrations of nitrate, sulfate, chloride, and sodium as well as pH and displayed a lower R-2 and slope in the validation set for fluoride. Nitrate and fluoride concentrations were estimated with errors lower than 15%, whereas chloride, sulfate, and sodium concentrations as well as pH were estimated with errors below 10%., The authors gratefully acknowledge the Ministerio de Economia y Competitividad and FEDER, providing funds amounting to (sic)664.525,75 for the project "Desarrollo de sistemas basados en lenguas electronicas para el control y monitorizacion del ciclo integral del agua" INNPACTO. IPT-2012-0069-310000. Moreover, the authors gratefully acknowledge the Ministerio de Economia y Competitividad and FEDER (projects MAT2015-64139-C4-1-R (MINECO/FEDER), MAT2015-64139-C4-3-R (MINECO/FEDER)), the Generalitat Valenciana (project PROMETEOII/2014/047), and CIBER-BBN (NANOPROBE project) for their financial support.

A humid electronic nose device based on pulse voltammetry has been applied to detect nerve agentsimulants in gas phase. The humid electronic nose consists in a polypropylene piece which containsan array of eight metallic electrodes (i.e., Ir, Rh, Pt, Au Ag, Co, Cu and Ni) divided into two sets of fourworking electrodes housed inside a homemade steel cylinder, and a salt bridge connection to a referenceelectrode. The electrochemical system is fitted to a nylon membrane damped with a background solutionof sodium tetraborate 0.01 M by a second polypropylene piece. The PCA analysis demonstrated that thesystem is able to discern principal organophosphorous nerve agent mimics (DCP, DCNP and DFP) fromorganophosphorous derivatives and some other potential interferents. Besides, the PLS quantificationanalysis showed sound accuracy in the concentration prediction for DCNP in air, good linearity and alimit of detection (LOD) of some a few ppm., Financial support from the Spanish Government (project MAT2012-38429-004) and the Generalitat Valenciana (project PROMETEO/2009/016) is gratefully acknowledged. L.P. is grateful to the Universitat Politecnica de Valencia for her grant.

Metallic implants placed in humans exhibit wear and corrosion that result in the liberation of metal-containing by-products. In the case of titanium (Ti) containing implants, the metal containing debris may exist in a number of states, including metallic particles produced by mechanical wear and the products of metal corrosion in biological environments, such as the joints and surrounding fluids and tissues. In addition, these constituents may dissolve in both intracellular and extracellular solutions generating Ti ions. Both species, ions and nanoparticles, show different cellular toxicities. In this work we have evaluated the possible evolution of TiO2 nanoparticles (NPs) into soluble Ti metal ions by contact with biological fluids. For this aim, an in vitro study to address quantitative Ti solubilisation from TiO2 nanoparticles (with a diameter of 21 nm) after incubation with human serum at different concentrations has been conducted. Total Ti determination revealed low solubilisation rates ranging from 0.53 to 0.82% after just one week of incubation in the serum. The incubated serum was then subjected to speciation analysis by anion exchange liquid chromatography using an inductively coupled plasma mass spectrometer (ICP-MS) as an elemental detector for Ti monitoring. The obtained results revealed a significant increase in the Ti signal associated with the fraction of the protein transferrin and preferentially with one of the metal binding sites of the protein, the N-lobe. Thus, the effect of Ti at the cellular level has been evaluated by considering that it can be present either as ions or as nanoparticles using two different cells lines: human enterocytes HT29 and murine osteoblasts MC3T3. Significant toxicity was found at the highest concentration assayed (50 μg mL(-1)) for both Ti species (ions and NPs) and slightly higher for the ionic species at lower concentrations (1 and 10 μg mL(-1)).

An electronic tongue has been developed to monitor the presence of ammonium nitrate in water. It is based on pulse voltammetry and consists of an array of eight working electrodes (Au, Pt, Rh, Ir, Cu, Co, Ag and Ni) encapsulated in a stainless steel cylinder. In a first step the electrochemical response of the different electrodes was studied in the presence of ammonium nitrate in water in order to further design the wave form used in the voltammetric tongue. The response of the electronic tongue was then tested in the presence of a set of 15 common inorganic salts, i.e., NH4NO3, MgSO4, NH4Cl, NaCl, Na2CO3, (NH4)2SO4, MgCl2, Na3PO4, K2SO4, K2CO3, CaCl2, NaH2PO4, KCl, NaNO3, K2HPO4. A PCA plot showed a fairly good discrimination between ammonium nitrate and the remaining salts studied. In addition Fuzzy Art map analyses determined that the best classification was obtained using the Pt, Cu and Ni electrodes. Moreover, PLS regression allowed the creation of a model to correlate the voltammetric response of the electrodes with concentrations of ammonium nitrate in the presence of potential interferents such as ammonium chloride and sodium nitrate.

A new electronic tongue to monitor the presence of glyphosate (a non-selective systemic herbicide) has been developed. It is based on pulse voltammetry and consists in an array of three working electrodes (Pt, Co and Cu) encapsulated on a methacrylate cylinder. The electrochemical response of the sensing array was characteristic of the presence of glyphosate in buffered water (phosphate buffer 0.1 mol·dm-3, pH 6.7). Rotating disc electrode (RDE) studies were carried out with Pt, Co and Cu electrodes in water at room temperature and at pH 6.7 using 0.1 mol·dm-3 of phosphate as a buffer. In the presence of glyphosate, the corrosion current of the Cu and Co electrodes increased significantly, probably due to the formation of Cu2+ or Co2+ complexes. The pulse array waveform for the voltammetric tongue was designed by taking into account some of the redox processes observed in the electrochemical studies. The PCA statistical analysis required four dimensions to explain 95% of variance. Moreover, a two-dimensional representation of the two principal components differentiated the water mixtures containing glyphosate. Furthermore, the PLS statistical analyses allowed the creation of a model to correlate the electrochemical response of the electrodes with glyphosate concentrations, even in the presence of potential interferents such as humic acids and Ca2+. The system offers a PLS prediction model for glyphosate detection with values of 098, -2.3 ¿ 10-5 and 0.94 for the slope, the intercept and the regression coefficient, respectively, which is in agreement with the good fit between the predicted and measured concentrations. The results suggest the feasibility of this system to help develop electronic tongues for glyphosate detection. © 2012 by the authors; licensee MDPI, Basel, Switzerland., Financial support from the Spanish Government (Project MAT2009-14564-C04-01 and PCI-Mediterraneo A/024590/09/A/ 03044/10), the Generalitat Valenciana (Project PROMETEO/2009/016), the UPV (project PAID-05-10) and its Centre de Cooperacio al Desenvolupament (Programa ADSIDEO-COOPERACIO 2010) is gratefully acknowledged.

In order to monitor the chloride penetration processes, a potentiometric embedded thick-film sensor was developed. This paper includes the results of research on the characterization of Cl− sensors made of Ag/AgCl resistive pastes (materials, sensitivity and detection limit, reproducibility, reversibility and response time, long-term performance and reliability in the presence of interfering agents). Theoretical expressions have been developed to describe the potentiometric response including the presence of OH− and bromide ions. The study shows that thick-film sensors are able to monitor Cl− activity as a function of the redox potential. Sensors are also capable of providing reliable and continuous real-time information on phenomena related to the progress of the chloride penetration front in concrete specimens. These sensors are a promising tool because thick-film technology allows us to obtain miniaturized, low-cost, robust and stable long-term sensors for Cl− monitoring., The pre-doctoral scholarship granted to Roman Bataller Prats within the program "Formacion de Personal Investigador (FPI) 2012" from Universitat Politecnica de Valencia is gratefully acknowledged.

Electronic equipment (IDM-1) especially designed for the application of voltammetric and impedometric electronic tongues is described. For impedance spectroscopy the equipment permits the generation of sinusoidal signals with a frequency in the range of 1 Hz to 1 MHz and programmable amplitude up to 1 Vpp. For voltammetry the IDM-1 equipment generates a sequence of up to 32 pulses with an amplitude that can be configured for each of the pulses in the range [-0.5; +0.5 V]. Voltammetric studies were performed using a total of eight working electrodes (i.e. Au, Pt, Ir, Rh, Ag, Cu, Ni, and Co) which were housed in a stainless steel cylinder used at the same time as both the body of the electronic tongue system and the counter/reference electrode. The width of the pulses can also be configured with a maximum value of 40 ms. The system consists of a software application that runs on a PC and electronic equipment. In order to test the capabilities of the designed system, impedometric and voltammetric measurements were carried out on five different commercial cola drinks (brands I-V). Three different waveforms were used in the voltammetric study (i.e. staircase, ascendant SAPV and descendant SAPV). The voltammetric response and the impedance phase and module values obtained were processed using PCA. A remarkable discrimination between all cola drinks was seen using the descendant waveform and a group of metal electrodes (Ni, Co, Cu, Ag). In contrast, impedance spectroscopy technique discriminated one brand (brand I) from the others. © 2012 Elsevier Ltd. All rights reserved., We thank MICINN (MAT2009-14564-C04-02) for a research fellowship.

This paper proposes a reasonable methodology for the design of pulse arrays applied in classification and quantification techniques based on the use of pulse voltammetric electronic tongues. As model problem we designed a procedure to predict levels of ferrocene, TCNQ and Ru(bipy)(3)(2+) using a voltammetric electronic tongue employing a set of noble electrodes; i.e. Au, Pt, Ir and Rh. Ferrocene, TCNQ and Ru(bipy)(3)(2+) have been selected as model compounds because these are molecules with well-defined redox processes. The electrodes were housed inside a stainless steel cylinder which was used as the body of the electronic tongue system. A SCE was used as reference electrode. An electrochemical study of the response of ferrocene TCNQ and Ru(bipy)(3)(2+) was carried out as a first step with the aim of characterise the redox processes in these compounds. Different samples containing ferrocene,TCNQ and Ru(bipy)(3)(2+) were prepared following an experimental design in which a system of three compounds/three levels was established. Multivariate analysis based on Partial Least Square (PLS) techniques was applied for data management and prediction models building. Several set of pulses were tested and a general procedure to their design for their use in voltammetric electronic tongues is discussed and proposed. (C) 2011 Elsevier B.V. All rights reserved., We thank the Spanish Government (projects MAT2009-14564-C04-01), Generalitat Valenciana (project PROMETEO/2009/016) for support. PCI-Mediterraneo A/024590/09/A/03044/10) and the UPV (project PAID-05-10) are gratefully acknowledged.

We report herein the use of a combined system for the analysis of the spoilage of wine when in contact with air. The system consists of a potentiometric electronic tongue and a humid electronic nose. The potentiometric electronic tongue was built with thick-film serigraphic techniques using commercially available resistances and conductors for hybrid electronic circuits; i.e. Ag, Au, Cu, Ru, AgCl, and C. The humid electronic nose was designed in order to detect vapours that emanate from the wine and are apprehended by a moist environment. The humid nose was constructed using a piece of thin cloth sewn, damped with distilled water, forming five hollows of the right size to introduce the electrodes. In this particular case four electrodes were used for the humid electronic nose: a glass electrode, aluminium (Al), graphite and platinum (Pt) wires and an Ag-AgCl reference electrode. The humid electronic nose together with the potentiometric electronic tongue were used for the evaluation of the evolution in the course of time of wine samples. Additionally to the analysis performed by the tongue and nose, the spoilage of the wines was followed via a simple determination of the titratable (total) acidity. © 2011 Elsevier B.V., We thank the Spanish Government (project MAT2009-14564-C04) and the Generalitat Valenciana (project PROME-TEO/2009/016) for support. Luis Gil-Sanchez also thanks the Universidad Politecnica de Valencia for support (Primeros Proyectos de Investigacion - PAID-06-09) and the Generalitat Valenciana (proyectos de I+D para grupos de investigacion emergentes - 2009/8650).

A method for predicting levels of sodium chloride, sodium nitrite and potassium nitrate in minced meat by using a combination of two different electrochemical methods; namely an electronic tongue (ET) based on pulse voltammetry and electrochemical impedance spectroscopy measurements is proposed here. The measurements with the voltammetric ET were carried out on both saline solutions (brines) and minced meat, whereas the impedimetric sensor was used only in minced meat. The addition of the salts was performed following an experimental design in which a system of three compounds/three levels was established. Multivariate analysis including Cross validation and Partial Least Square (PLS) techniques were applied for data management and prediction models building. A very good prediction of the concentration of chloride was achieved, whereas the prediction for the concentration of nitrate and nitrite can be considered as moderate.

The measurement of salt content in processed products still remains a problem to solve in the food industry due to the destructive nature of the conventional measurement methods. In this paper a method to assess salt content in food products such as cured ham or pork loin using impedance spectroscopy is presented. A low-cost system to carry out a punctual measurement of the impedance inside the food sample based on a non-destructive sensor was developed. The system includes an electronic equipment that allows the implementation of impedance spectroscopy and an electrode consisting of a coaxial needle. In order to validate the equipment, solutions with different salt concentrations were measured. The impedance modulus and phase values obtained for each frequency were processed using PLS; the results show a very good correlation between predicted and observed data. The same process was carried out on minced meat samples and again a good correlation was obtained. The PLS tool generated a model that permits prediction of salt levels in new meat samples.

[EN] An electronic tongue (ET) based on pulse voltammetry containing a set of eight metallic electrodes (Au, Pt, Ir, Rh, Cu, Co, Ni and Ag) encapsulated on a stainless steel cylinder has been used to discriminate and predict levels of nerve agent mimics in aqueous environments. Analysis including principal component analysis (PCA) and partial least square techniques (PLS) have been applied for data management and prediction models. A good discrimination from other organophosphorous derivatives was found for the nerve agent simulants diethyl-chlorophosphate (DCP) and diethyl-cyanophosphate (DCNP)., We thank the Ministerio de Ciencia y Tecnologia (project CTQ2006-15456-C04-01), and Universidad Politecnica de Valencia (project PAID-06-07-3243) for support. I.C. thanks the Universidad Politecnica de Valencia for a Doctoral Fellowship.

Based on the cross-sensitivity shown by certain metal electrodes for some anions in a liquid media, an array of five potentiometric electrodes (Au, Ag, Pt, Cu and Zn) has been used as an electronic tongue device for the recognition and prediction of common anions chloride, sulfate and bicarbonate in mineral waters. The recognition testing studies included measurements of potential (emf) on solutions of pure salts, mixtures of salt and some mineral waters. Predictions were performed by using partial least square. A good discrimination between different water samples by PCA analysis was found as well as an adequate prediction of the concentration of chloride and sulfate.

Electronic tongues were developed some ten years ago. These systems consist of an array of nonspecific sensors and a signal processing unit. The sensor signals are processed by pattern recognition methods which makes possible the extraction of specific properties from the sample. Depending on the calibration, attributes such as quality or taste can be determined. These systems also detect changes in the sample that they are not calibrated for which makes possible the detection of anomalous occurrences. Such sensor systems are suitable for process control and surveillance. Important factors are the sensitivity and stability, specifically the sensor's ability to respond to small changes and to provide true and reproducible readings over time. Problems with sensor stability are commonly referred to as drift. The major topic of this thesis is the improvement of long term stability for electronic tongues used in liquid process applications. Drift counteractions, such as renewal of the electrode surface by polishing, was compared with mathematical correction methods. Since drift is induced by the environment of the sensor, mathematical correctional actions must include reference samples and the induced drift must be identical between measurements. These conditions restrict and complicate the use of mathematical drift counteractions. It was found that mechanical polishing renewed the electrode surfaces, and that the induced drift was unique for each sample. The sample induced drift pattern can be treated as information from the sample, but only if the sensors are renewable in a repeatable way. Applications where polishing the electrode surfaces are necessary to obtain repeatable analyses are described, such as the detection of urea and measurements in corrosive environments such as wine. Electrochemical oxidation of urea in water is difficult to use for analytical purposes because of residues left on the electrode surface. An important result from this thesis is that mechanical cleaning of the electrodes between samples gives sensor signals that are both repeatable and proportional to the concentrations of urea and glucose. An experimental design was employed for optimal effect of the calibration of urea in the presence of glucose as a disturbance in the sample. The goal was to minimize the correlation between the two analytes. This made possible the prediction of both analyte concentrations. Wine is a complex sample to analyze with many sources of disturbances for electrochemical measurements. The carefully planned experiments and calibrations reported in this thesis minimized covariance and background effects. A method for prediction of bisulfite, histamine and ascorbic acid concentrations in wine was developed. The method was tested with spiked samples of white-, red-, rose-wines and even apple juice. The reproducibility of the measurements was excellent. Since polishing renewed the electrodes between measurements, a validation performed one month after the calibration was also predicted with good results. This demonstrated that the renewal of the electrodes eliminated special requirements for maintenance and storage of the sensor. Drinking water surveillance has been performed with an electronic tongue. The potential of using a voltammetric electronic tongue for multicomponent analysis of compounds in drinking water has been evaluated. By using such a non-selective sensor it was possible to detect anomalies without the need of a specific sensor for each type of event. The device can be calibrated for the most likely events, and it can also be used for sensing and alarm when exceptional events occur. The detection of surface active species like detergents is normally done by titration. An in-line sensor that could control the washing process by detecting the concentrations of detergents during the different steps in a wash cycle could enhance the performance of washing machines. An electronic tongue was used to predict concentrations of detergents in samples from different stages in the washing procedure. The tongue was compared with a much simpler conductivity meter, and due to the covariation of supporting electrolyte, both sensors were able to predict concentrations of ionic surfactants. The electronic tongue showed promising results in predicting also non ionic surfactants where the conductivity meter failed. The detection mechanism was probably due to shielding the electrode surface from electro active species in the samples.

We report on the development of an electronic tongue as potential tool for fish freshness determination. The studies were carried out following the evolution with time on fillet of cultured sea bream (Sparus Auratus). The electronic tongue consists of 16 potentiometric electrodes of the type metal, metal oxide and insoluble metal salts. Graphite was also used as electrode. Fish freshness indicators such as texture, pH, colour, microbial analysis, total volatile basic nitrogen (TVB-N) and biogenic amines were also determined versus time. The effectivity of the electronic tongue in the assessment of the evolution with time of fish fillets was evaluated. First the electronic tongue was used to classify samples according to time. Perceptron and adaptive resonance theory were used to discriminate between the data from different days. In a second step, the electronic tongue was used to predict the results obtained from chemical and biochemical analyses by building quantitative partial least square (PLS) models. A remarkable correlation was found between the electronic tongue formed by the 16 simple electrodes and parameters such as total biogenic amines, pH, TVB-N and microbial analysis with correlation coefficients larger than 0.98.

In the composition of commercial RuO 2 -containing resistive pastes there is also a significant amount of other electro-active metal oxides. Thus, when the pastes are used in the manufacture of thick-film electrodes, the electrochemical response is a complex contribution of all the electro-active metal oxides included in the paste composition. This is an attractive complex system whose electrochemical response has been studied and explained using a model based on surface activity changes of the solids involved in the redox processes. The developed model is able to describe the redox potential of the electrode as a function of the pH and explain the presence of certain anionic interferences.

A new definition for the electrochemical cell constant in conductivity measurements is presented in this paper. Electrochemical Impedance Spectroscopy and DC pulses measurements have been carried out in non-Faradaic conditions in order to evaluate the effects of the cell geometry. The results obtained demonstrate that conductivity measurements are affected not only by the electrodes surface and separation but also by the cross section of the electrochemical cell. In order to obtain a linear behavior of the resistance versus the distance between electrodes, the cross section of the cell should be equal to the electrodes surface. Differences between the cell cross section and the electrodes surface produce a heterogeneous distribution of the electric field that causes the non-linear behavior for low values of the electrodes separation. This study shows that the reproducibility in electronic tongue and humid electronic nose measurements can be improved by designing an electrochemical cell structure that warrants a homogeneous distribution of the electrical field, which results in a reduction of the detection threshold in these types of system., Financial support from the Spanish Government (projects MAT2012-38429-C04-04 and IPT-2012-0069-310000) is gratefully acknowledged. The pre-doctoral scholarship granted to Roman Bataller Prats within the program "Formacion de Personal Investigador (FPI) 2012" from Universitat Politecnica de Valencia is gratefully acknowledged.

An electronic tongue for the qualitative analysis of aqueous solutions of salts hasbeen developed. The following set of electrodes was used: RuO 2 , Ag, and Cu in thick-filmtechnology and Au, Pb, Zn and Ni as small bars of the corresponding metal. The response ofthe designed “electronic tongue” was tested on a family of samples containing pure salt andcomplex mixtures. The electrodes were used as potentiometric un-specific sensors and thee.m.f. of each electrode in contact with a certain aqueous solution was used as input signalfor a PCA analysis. The study showed that the set of electrodes were capable to discriminatebetween aqueous solutions of salts basically by their different content in anions and cations(the anions SO 42- , Cl - , PO 4 H 2- , CO 3 H - , NO 3- and cations Na + and K + were studied). In orderto better analyze the basis for the discrimination power shown by the electronic tongue, aquantitative analysis was also envisaged. A fair estimation of the concentrations of thedifferent ions in the solutions studied appeared to be possible using this electronic tonguedesign.

We report here a general model for the description of the redox potential behaviour of certain electrodes in complex mixtures based on the study of redox process. The model has been developed theoretically and has also been experimentally verified. The model allows to state broad-spectrum equations which describe the behaviour of the potential of second and third order Faradic electrodes. Experimental verification of the model was carried out using common redox electrodes. The model was used to predict the redox behaviours in the following cases; (i) study of the potential variation of a Silver electrode as function of the pH, (ii) the redox potential of an Ag/AgCl electrode as function of the chloride concentration at different pH values, (iii) the potential of a Ag/AgBr electrode in the presence of certain amounts of chloride and (iv) the quantitative solid–solid transformation between AgBr and AgCl phases. There was found a remarkably good agreement between the experimental and theoretical values.

A set of sensors for water quality measurement has been developed. It consists of a multisensor designed to measure the following parameters: pH, temperature, dissolved oxygen, conductivity, redox potential and turbidity. The system has been built-up in thick-film technology, using when possible commercially available serigraphic pastes. The multisensor can be implemented in in situ portable or stationary instrumentation for water quality monitoring. The technology used in the multisensor implementation provides fundamental properties of miniaturization, reasonable precision and low cost. The complete system also includes electronic acquisition, signal conditioning and computing capabilities.

A new “electronic tongue” has been developed and used for the qualitative analysis of natural waters. Both wires and conducting surfaces in thick-film technology were used as potentiometric electrodes and the emf of each electrode in contact with a certain aqueous solution was used as input signal for a PCA analysis. An array containing the electrodes; RuO2 (with resistivities of 10 � /sq and 1 M� /sq), C, Ag, Ni, Cu, Au, Pt, Al, Sn, Pb and C (graphite) were used in a first approach. To test this “electronic tongue” design, a family of different natural waters were studied. These include seven mineral waters, tap water and osmotised water. Additionally, a qualitative analysis of the different waters was performed using fuzzy ARTMAP neural networks. The final system was successfully employed for the differentiation of the above mentioned waters with a success rate higher than 93%. © 2004 Elsevier B.V. All rights reserved.

A strategy for the rational design of a new optical sensor material for the selective recognition of long-chain carboxylates in water is presented. The approach relies on the combination of structure-property relationships to single out the optimal molecular sensor unit and the tuning of the sensing characteristics of an inorganic support material. A spacer-substituted 7-urea-phenoxazin-3-one was employed as the signaling moiety and a mesoporous trimethylsilylated UVM-7 (MCM-41 type) material served as the solid support. The sensor material shows the advantageous features of both modules that is absorption and emission in the visible spectral range, a fluorescence red-shift and enhancement upon analyte coordination, and the amplification of noncovalent (binding) and hydrogen-bonding (recognition) interactions in the detection event. Besides these basic results that are related to the design and performance of the sensor material, the paper discusses general aspects of amido-substituted phenoxazinone photophysics and addresses some general features of molecular anion recognition chemistry in aqueous vs nonaqueous media, utilizing steady-state and time-resolved optical as well as NMR spectroscopies. Detailed studies on potentially competing biochemical species and a first access to the schematic model of the response of the sensor material as obtained by a combination of fluorescence lifetime distribution analysis and Langmuir-type fitting of the gross binding constants complement the key issues of the paper.

The new cyclic aza-oxa-cycloalkane 7,13-bis(n-octyl)-1,4,10-trioxa-7,13 diazacyclopentadecane (L1) has been synthesised, characterized and its interaction with anionic surfactants studied. Protonation constants of L1 and stability constants of L1 with lauryl sulfate, sulfate and phosphate were determined by potentiometric titration in 1,4-dioxane:water (70:30, v/v, 0.1 mol dm−3 KNO3, 25 °C). L1 forms stable complexes with lauryl sulfate in a wide pH range. Different PVC-membrane anionic surfactant-selective electrodes were prepared using L1 as ionophore and o-nitrophenyl octyl ether (NPOE), bis(2-ethylhexyl) sebacate (BEHS) or dibutyl phthalate (DBP) as plasticizers. The PVC-based membrane electrode containing L1 as carrier and NPOE as plasticizer (electrode E1) showed a Nernstian response with a slope of 57.7 ± 0.2 mV per decade over a range of lauryl sulfate concentration from 3.3 × 10−6 to 6.7 × 10−3 M with a detection limit of 2.2 × 10−6 M. For the sake of comparison, a PVC-based membrane electrode containing L1, NPOE and tetra-n-octylammonium bromide as cationic additive (electrode E2) was also prepared and studied. Selectivity coefficients for different anions with respect to lauryl sulfate were calculated. Electrode E1 showed remarkably better selectivity coefficients than electrode E2, probably due to favourable interaction of lauryl sulfate with L1. Electrode E1 was used for the determination of anionic surfactants in several mixtures, and the results obtained were compared to those found using a commercially available electrode.

A general model concerning the role of the electrode potential on the charge-transfer enhancement mechanism of SERS is proposed, justifying the existence of a parameter ‚ which reduces the effectiveness of the electrode potential in order to shift the excited charge-transfer level. This explains the observed deviation of ‚ from the unity, and allows for relating the intensity/electrode-potential (SERS -CT) profiles of similar adsorbates with the respective electron affinities. The SERS of pyridine, pyrazine and methylpyrazines have been recorded on silver, being found that the electrode potential in the maximum of the SERS-CT profiles shifts toward more negative values as the number of methylsubstituents attached to the pyrazine ring increases. This result has been explained on the basis of the relative stability of the radical anions given that a correlation between those shifts and the calculated ab initio vertical transition energies between the neutral molecules and their respective radical anions can be established. This confirms the participation of a resonant charge-transfer mechanism in the SERS as well as the usefulness of this technique to gain insight into the electronic properties of the doublet states of the here studied molecules.

The surface-enhanced Raman scattering (SERS) spectra of 4-methylpyridine (4-MP) have been recorded at different electrode potential versus saturated Ag/AgCl/KCl reference electrode. By comparing the relative intensity of the SERS with the Raman spectrum of the aqueous solution it is possible to determine that 12, 6a, δ(CH) and especially 8a modes are strongly enhanced. In this work, it is demonstrated that these vibrations are closely related to Franck–Condon factors of a resonant photoinduced charge transfer (CT) mechanism similar to a resonance Raman (RR) process. The theoretically calculated ΔQ displacements represent the differences between geometries of the potential energy minima of the states involved in the resonant process, allowing to calculate the relative intensities in RR from the Peticolas’ equation. These calculated intensities are in a perfect agreement with the experimental behavior.

The surface-enhanced Raman scattering spectra of 2,6-dimethylpyridine have been recorded on silver at different electrode potentials. The main feature of these spectra is the strong enhancement of the band corresponding to the 8a mode when the electrode potential becomes more negative. This enhancement has been discussed on the basis of a resonant charge transfer (CT) mechanism by using a methodology based on the analysis of the ab initio optimized equilibrium structures of the electronic states involved in the CT resonant process namely: the ground electronic states of the neutral molecule and its radical anion.

The ligand 1,4,8-tri(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L1) containing pendant octyl groups has been synthesised. L1 is a tetraazamacrocycle derived from the well-known cyclam unit, and the Ni2+ and Co2+ complexes, [Ni(L1)]2+ and [Co(L1)]2+, have been isolated and characterised. The ability of the nickel(II) and cobalt(II) complexes to act as anion receptors has been studied by using them as ionophores in membrane-based ion-selective electrodes (ISEs). The PVC membrane containing the complex [Ni(L1)]2+ and 2-nitrophenyloctylether as plasticizer shows a Nernstian response against iodide in a concentration range from 1×10−1 to 4×10−5 M I− with a detection limit of 1.6×10−5 M I− and a slope of 58.6 mV/pI− at pH 7 (25 °C). In comparison, the electrode containing [Co(L1)]2+ as ionophore gave a sub-Nernstian slope and a low lifetime. A comparison between the iodide-selective electrode containing [Ni(L1)]2+ and other reported iodide-selective electrodes is also reported.

Surfaced-enhanced Ramon scattering (SERS) spectra of pyrazine are analyzed on the basis of the properties of the electronic states of the metal-adsorbate surface complex. Ab initio CIS calculations have been carried out for the Ag2-pyrazine complex, which have enabled us to find two excited singlets, namely CT0;1B1 and CT1;1A2, with properties quite similar to those of the pyrazine radical anion in its electronic 2B3u and 2Au states, respectively, and with energies falling in the range of the exciting photons usually employed in Raman spectroscopy. SERS spectra of pyrazine are compatible with a resonance Raman enhancement mechanism involving electronic transitions between the ground state S0;1A1 and both CT levels of the surface complex.

The observed shifts of the vibrational SERS frequencies with respect to those of the Raman spectrum of pyrazine have allowed us to conclude that the molecule adsorbs to the metal through the unshared electron pair of one of the nitrogen atoms. The same conclusion is reached by observing the behavior of the molecular vibrations when the electrode potential is changed. Only one type of molecules has been found with orientation perpendicular to the metal surface in the whole range of potentials studied. These conclusions are supported by the comparison of the experimental data with the ab initio results obtained for the vibrational frequencies of pyrazine isolated and coordinated to several conveniently selected silver clusters.

Ammonia (NH4 N) and orthophosphate (PO4 P) quantification in wastewater treatment plants is important due to their implication in the eutrophication process. A voltammetric electronic tongue as a tool for the prediction of ammonia and orthophosphate concentrations from influent and effluent wastewater is proposed herein. An electrochemical study of the response of the ammonium and orthophosphate ions was performed in order to design a suitable waveform for each electrode. Partial Least Squares analysis was used to obtain a correlation between the data from the tongue and the concentrations of ammonia and orthophosphate measured in the laboratory showing good predictive power., Financial support from the Spanish Government (Project MAT2012-38429-C04-01) and the Generalitat Valencia (Project PROMETEO/2009/016) is gratefully acknowledged.

Recently, we have implemented a method to obtain automatically a quantum mechanical scaled force field within the procedure of Pulay. In the present work, the performance of this method is checked by taking large molecules as example tests: anthracene and naphthalene. Additionally, in order to improve the agreement between calculated and observed vibrational frequencies, the scaled force fields are refined using a new method also developed by us. The starting force fields of these molecules are obtained from a DFT/B3-LYP calculation by using the 6-31G ∗ basis sets.

An algorithm for scaling a vibrational force field is developed and implemented in a computer program. A method to label the calculated frequencies is developed as well, that allows the automatic application of such program to any force field, independently of the level of theory used to generate it. This procedure has been tested with the scaled force fields of pyrazine and pyridine and the results have been completely satisfactory.

The established Pulay's method of scaling quantum mechanically computed quadratic force fields of moderately complex molecules is used to calculate reliable vibrational frequencies of transition states in unimolecular decomposition reactions. The basic hypothesis is the transference of the scale factors computed for the molecule in its ground state to the transition state provided that the same internal coordinates are defined. The rate limiting step is the nitrogen elimination reaction in every case and reduced potential energy surfaces have been computed at AM1 and HF/4-31G levels for methylazide and ethylazide. The respective transition states have been identified and pre-exponential factors of the rate constant have been computed.

Potentiometric and electrochemical studies have been carried out in THF–H 2 O (60:40 v/v) and H 2 O on several ferrocene-containing pH-responsive molecules and the acidity constants of the reduced species (K m ), the ‘oxidised’ species (K m n ) and the maximum oxidation potential shift due to the binding process of L with protons (ΔE) have been determined. From these values, and ΔE data in MeCN, MeCN–H 2 O (80:20 v/v), THF–H 2 O (80:20 v/v) and H 2 O, an empirical equation based on a Coulomb charge model, is obtained which accounts for the maximum oxidation potential shift as a function of the charge of the oxidised electroactive framework, the charge of the substrate, the number of electrons involved in the electrochemical process, the number of redox-active units, the distance between the redox-active groups and the substrate and the macroscopic relative permittivity of the medium.

Recently, electronic tongues (ET) have appeared as an excellent alternative to traditional techniques for the evaluation of food quality and processes. ET systems are based on arrays of low selectivity sensors that are simultaneously sensitive to several components in a measured sample (cross-sensitivity). The aim of this study was to determine the ability of an ET based on pulse voltammetry to quantify organic acids (ascorbic, citric and malic acids) in simple (SS) and binary solutions (BS) using different electrodes. The most significant electrodes for ascorbic acid prediction were Ni and Ag for SS, and Ag and Ir for BS where positive pulses were more suitable than negative ones. The prediction of citric and malic acids in SS and BS were suitable using Ir, Rh, Pt, Ag and Cu electrodes, using both positive and negative pulses., We would like to thank the Spanish Government for support (projects AGL2010-20539- subprograma ALI and MAT2009-14564-C04-02). The translation of this paper was funded by the Universitat Politecnica de Valencia, Spain.