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Presentamos la evaluación de los electrodos de carbono vítreo (GC) modificados con películas de Nafion (Nf) y depósitos bimetálicos de aleaciones Ag-Hg y Ag-Bi. La mayoría de los bimetálicos depositados, con un tamaño promedio de aproximadamente 150 nm, se dispersaron e incrustaron uniformemente dentro de la red del Nafion, mientras que una cantidad mucho menor permaneció encima de las incrustadas sin ninguna orientación regular, como lo indica imágenes de microscopía electrónica de barrido (SEM) y microscopía de fuerza atómica (AFM). Las pruebas de sensibilidad para el electrodo modificado AgBiNf/GC produjeron límites de detección (DL), basados en la variabilidad de una solución en blanco (criterio de 3 s), de 0,78 y 0,66 μg L-1 para Cd (II) y Pb (II), respectivamente; mientras que el DL sobre el electrodo modificado AgHgNf/GC fue 0,17 y 0,24 μg L-1 para Cd (II) y Pb (II), respectivamente. La precisión de la metodología por voltametría de redisolución anódica se verificó mediante el cálculo de porcentajes de recuperación de los dos analitos, expresados como error relativo. Se logró una recuperación del 99% al 92%.

RESUMEN En este trabajo se comunica el diseño y optimización de parámetros operacionales de una celda para generar electroquímicamente arsina (AsH3) gaseosa (g), fácilmente acoplable a un espectrofotómetro de absorción atómica; como técnica de introducción de muestra para la cuantificación de As en sedimentos marinos de la Comuna de Bajoalto, Provincia de El Oro, Ecuador los cuales están afectados por la contaminación debida a actividades antropogénicas. La exactitud, RSD y precisión dentro del método de cuantificación reportado en este estudio, se determinó As en materiales de referencia, optimizando un método de preparación de muestra basado en digestiones ácidas. Se obtuvo un límite de detección sobre cátodos de oro/mercurio (Au/Hg) de 0,027 μg L-1(ppb). ABSTRACT In this work, the design and optimization of operational parameters of a cell to generate electrochemically gaseous arsine (AsH3), easily coupled to an atomic absorption spectrophotometer, are communicated; as a sample introduction technique for the quantification of As in marine sediments of the Bajo Alto Community, Province of El Oro, Ecuador, whatever is affected by contamination due to anthropogenic activities. The accuracy, RSD and precision within the quantification method reported in this study, was determined using reference materials, optimizing a sample preparation method based on acid digestions. A detection limit on gold / mercury cathodes (Au / Hg) of 0,027 μg L-1 (ppb) was obtained.

Glyphosate [N-(phosphonomethyl)-glycine] is a herbicide with several commercial formulations that are used generally in agriculture for the control of various weeds. It is the most used pesticide in the world and comprises multiple constituents (coadjutants, salts, and others) that help to effectively reach the action’s mechanism in plants. Due to its extensive and inadequate use, this herbicide has been frequently detected in water, principally in surface and groundwater nearest to agricultural areas. Its presence in the aquatic environment poses chronic and remote hazards to human health and the environment. Therefore, it becomes necessary to develop treatment processes to remediate aquatic environments polluted with glyphosate, its metabolites, and/or coadjutants. This review is focused on conventional and non-conventional water treatment processes developed for water polluted with glyphosate herbicide; it describes the fundamental mechanism of water treatment processes and their applications are summarized. It addressed biological processes (bacterial and fungi degradation), physicochemical processes (adsorption, membrane filtration), advanced oxidation processes—AOPs (photocatalysis, electrochemical oxidation, photo-electrocatalysis, among others) and combined water treatment processes. Finally, the main operating parameters and the effectiveness of treatment processes are analyzed, ending with an analysis of the challenges in this field of research.

The evaluation and application of glassy carbon electrodes modified with bimetallic nanoparticle deposits of Ag–Hg and Ag–Bi for determination of Pb(II) is described. Deposition of the nanostructured bimetallic combinations on top of the glassy carbon (GC) substrate, previously covered with a Nafion (Nf) film, resulted in electrodes with substantially enlarged hydrogen evolution over-voltage. As indicated by scanning electron microscopy and atomic force microscopy images, most of the deposited nanoparticles, with an average size of 150 nm, were uniformly dispersed inside the Nafion net while a smaller amount remained on top of the embedded ones. Sensitivity tests of the AgBiNpNf/GC modified electrode produced a detection limit (DL), based on the 3s criterion, of 0.66 μg L−1 and 0.24 μg L−1 for the AgHgNpNf/GC electrode. Accuracy was assessed by comparison with quantification of Pb(II) in human blood serum and urine samples analyzed by atomic absorption spectrometry, using a continuous source high resolution atomic absorption spectrometer.

Long-term cadmium intake can be very dangerous to human health due to its toxic effects. Although people can be contaminated with this element from different sources, contaminated food is probably the most important one. Foods such as vegetables and fruits can become contaminated with cadmium existing in soils, irrigation water, or chemical fertilizers. Some plants produce an excess of cysteine-rich peptides (CRp) when affected by high concentrations of heavy metals such as cadmium, thus indicating the presence of this type of contamination. Among these plants is tamarillo (Solanum betaceum), which is locally known as &ldquo, tree tomato&rdquo, This is a native plant widely consumed in the Ecuadorian Andes because of its abundance, low cost, and high content of vitamin C and fiber. The fact that Solanum betaceum produces CRp upon contamination with heavy metals means that this plant may be able to accumulate heavy metals. If this is the case, the plant can possibly be used as an indicator of metal pollution. The main goals of the present work were to evaluate the possibility of using Solanum betaceum as an indicator of metal contamination in plants and to examine its capability to accumulate metals. Both goals were met by determination of the amounts of CRp produced by Solanum betaceum cells cultivated in vitro in the laboratory under controlled conditions in the presence of different concentrations of cadmium. The CRp determination was carried out by means of electrogeneration of iodine in an iodide solution containing reduced glutathione as a biological thiol model. Solanum betaceum cells were grown in a Murashige and Skoog solution enriched with a 30 g L&minus, 1 sugar aqueous solution and 1 mg L&minus, 1 2,4-dichlorophenoxyacetic acid. The results of these experiments confirmed the following: (1) CRp production is a function of the amount of cadmium present as a contaminant up to a limiting value after which cell apoptosis occurs, (2) Solanum betaceum accumulates cadmium, (3) the analytical method used is appropriate for CRp determination, and (4) CRp determination is a valid alternative to detect contamination by heavy metals in plants.

We modified and evaluated the performance of a CuO/Cu electrochemical electrode for chemical oxygen demand (COD) determination by covering it with a Nafion (Nf) film. The resulting modified CuONf/Cu electrode sensor was used for the electrochemical determination of COD in river, slaughterhouse and estuarine water samples in order to evaluate its performance for this particular task. It was compared with the CuO/Cu sensor with no Nafion. The main electrochemical characteristics of interest, resistance, sensitivity, accuracy and reproducibility, were assessed by means of Linear Sweep Voltammetry using glucose as a standard. Results of these essays indicate that the procedure used produced smooth and firmly attached Nf films covering the whole copper surface. This sensor was shown to be resistant to interferences and effective in electro-oxidation of a wide range of organic compounds and therefore very useful for COD determination. Using the newly developed CuONf/Cu electrode an analytical linear range of 50 to 1000 mg&middot, L&minus, 1 COD, with a detection limit of 2.11 mg&middot, 1 (n = 6) COD was achieved. The comparison shows that the CuONf/Cu sensor is more appropriate for COD determination than its counterpart with no Nafion.

The electrochemical generation of antimony volatile species (stibine) using Au and Ag mercury amalgamated cathodes is described. Compared with some other cathode materials commonly used for electrochemical hydride generation, performance of the amalgamated cathodes is substantially better in the following aspects: higher interference tolerance, higher erosion resistance and longer useful working time. Using the amalgamated cathodes, it could be shown that interferences from major constituents at high concentrations, especially from transition metals, affecting stibine generation are not as significant as they are using other cathode types in regards to sensitivity and useful working time. Results obtained using the Ag/Hg amalgamated cathode showed a slightly higher sensitivity than the corresponding results obtained using the Au/Hg cathode. The Au/Hg cathode, which to our knowledge has not previously been used to generate stibine, showed considerably longer useful working time than the Ag/Hg one. The optimum catholytes for electrolytic generation of stibine (SbH 3 ) from Sb(III) and Sb(V) using the Au/Hg electrode were aqueous solutions containing 0.5 mol L −1 H 2 SO 4 and 0.5 mol L −1 HCl, respectively. Under optimized conditions, using the Au/Hg cathode and comparing to aqueous standards calibration curves, detection limits (3 σ ) of 0.027 µg L −1 for Sb(III) and 0.056 µg L −1 for Sb(V), were obtained. To check accuracy a marine sediment reference material (PACS-2, NRC) was analyzed using a method purportedly developed for this task. Good agreement, 95% confidence, was found between the certified and the experimental values for Sb. The proposed method was also applied to the determination of Sb in aqueous solutions of marine sediments samples from Comuna de Bajo Alto Provincia de El Oro—Ecuador. Recoveries of five replicate determinations of these samples were in the range of 98–103% thus showing acceptable accuracy in the analysis of real samples.

The electrochemical generation of arsenic volatile species (arsine) using an Au/Hg amalgam cathode in a 0.5 M H2SO4 solution, is described. Results were compared with those obtained with other cathodes commonly used for generation of arsine. The effects of the electrolytic conditions and interferent ions have been studied. Results show that the Au/Hg cathode has better tolerance to interference and higher repeatability than cathodes made out of platinum (Pt), gold (Au), reticulated glassy carbon (RGC), lead (Pb). Under optimized conditions, a 0.027 μg L−1 (3σ) detection limit for As(III) in aqueous solutions and a 2.4% relative standard deviation for a 0.1 μg L−1 As(III) were obtained. The accuracy of the method was verified by determination of As in a certified reference material. The proposed method was applied to the determination of As in spiked tap water samples.

We report on two new electrochemical sensors which, coupled to differential pulse voltammetry, constitutes a useful tool for diagnosis of heavy metal pollution. The electrochemical sensors AgHgNf/Cu and the AgBiNf/Cu were obtained by deposition of bimetallic particles of AgHg or AgBi on copper electrodes covered with a Nafion (Nf) film, respectively. Micrographs of the electrode&rsquo, s surface showed evenly scattered bimetallic particles, with an approximate diameter of 150 nm, embedded in the Nafion (Nf) film. In order to test the electrodes, the hydrogen evolution signal according to the Brdička reaction was measured for the determination of cysteine-rich peptides (CRp) produced by plants. To check the accuracy of the electrodes, real samples of Nicotiana tabacum cells exposed to cytotoxic levels of cadmium were tested. The AgHgNf/Cu electrode produced detection limits (DLs) of 0.088 &micro, mol L&minus, 1 for Cysteine and 0.139&micro, 1 for Glutathione, while for the AgBiNf/Cu electrode DLs were 0.41 &micro, 1 for cysteine and 0.244 &micro, 1 for glutathione. Thus, the new electrodes could be a useful analytical electrochemical system very convenient for fieldwork. The electrodes were capable of direct, accurate, and sensitive detection of synthesized peptides, despite the complex matrix where the Nicotiana tabacum cells were grown.

We have developed an anodic stripping voltammetry method that employs carbon fiber ultra-microelectrodes modified with gold nanoparticles to determine arsenic in natural waters. Gold nanoparticles were potentiostatically deposited on carbon fiber ultra-microelectrodes at −0.90 V (vs SCE) for a time of 15 s, to form the carbon fiber ultra-microelectrodes modified with gold nanoparticles. Cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy coupled to an X-ray microanalysis system were used to check and confirm the presence of gold nanoparticles on the carbon fiber ultra-microelectrodes. Arsenic detection parameters such as deposition potential and deposition time were optimized allowing a detection range between 5 to 60 µg L -1 . The developed modified electrodes allowed rapid As determination with improved analytical characteristics including better repeatability, higher selectivity, lower detection limit (0.9 μg L -1 ) and higher sensitivity (0.0176 nA μg L -1 ) as compared to the standard carbon electrodes. The analytical capability of the optimized method was demonstrated by determination of arsenic in certified reference materials (trace elements in water (NIST SRM 1643d)) and by comparison of results with those obtained by hydride generation atomic absorption spectrometry (HG-AAS) in the determination of the analyte in tap and well waters.

Working electrodes made out of pyrolytic graphite, glassy carbon, platinum and cadmium were compared for the electrochemical generation of volatile lead species. The same electrolytic cell, using each of the different working electrodes was coupled to an atomic absorption spectrometer and the experimental conditions were optimized in each case, using a univariate approach, to produce the maximum possible amount of volatile lead species. The experiments were focused on the variation of cathode hydrogen overvoltage by the application of a constant current during analysis. Under optimum conditions the performance of the electrochemical hydride generator cell should depend on the cathode material selected due to the different hydrogen overpotential of each material. The lead absorbance signal was taken as a measure of the efficiency of volatile lead species production. Best results were obtained using the Cd cathode, due to its relatively highest hydrogen overpotential, a carrier gas (Ar) flow rate of 55 mL min − 1 an electrolytic current of 0.8 A and a catholyte (HCl) concentration 0.05 mol L − 1 . The analytical figures of merit of the method using the Cd electrode were evaluated and the susceptibility of the method to interferences was assessed by its application to the determination of trace amounts of lead in the presence of the most significant interferents. The calibration curve was linear between 0.5 and 15 μg L − 1 Pb. Detection limits and characteristic mass values were 0.21 μg L − 1 and 0.26 μg L − 1 respectively. A bovine liver standard reference material and a spiked urine sample were analyzed to check accuracy.

A micro/nanoparticle ( μ-NP ) bismuth film electrode (BiFE) has been developed for the determination of lead and cadmium by anodic stripping voltammetry (ASV) and trace levels of chromium by adsorptive stripping voltammetry (AdSV). Chromium was detected in a flow cell. Bismuth was electrodeposited on a hydrated aluminum oxide template, which was previously coated on a glassy-carbon (GC) electrode. Then, the template was selectively removed by soaking the electrode in a 0.1 M NaOH solution for 30 min, leaving a dispersed bismuth film covering the electrode surface; such electrodeposits had a particulate appearance, which was observed by scanning electron microscopy (SEM). The voltammetric analyses from a chromium solution on a μ-NPs /BiFE provided a limit of detection (LOD) equal to 0.12 ng L −1 ( n = 6) and a slope of 0.27 μC/ng L −1 ( R 2 = 0.9903). The signals registered were more than 50 times higher than the peaks obtained from a conventional BiFE. The analysis of aqueous solutions of Cd and Pb gave also lower LOD and higher sensitivity against the conventional BiFe experiments.

We report about the use of carbon paste electrode modified with kaolinite for analytical detection of trace lead(II) in domestic water by differential pulse voltammetry. Kaolinite clay was modified with tripolyphosphate (TPP) by impregnation method. The results show that TPP in kaolinite clay plays an important role in the accumulation process of Pb(II) on the modified electrode surface. The electroanalytical procedure for determination of Pb(II) comprised two steps: chemical accumulation of the analyte under open-circuit conditions, followed by electrochemical detection of the pre-concentrated species using differential pulse voltammetry. The analytical performance of this system has been explored by studying the effects of preconcentration time, carbon paste composition, pH, supporting electrolyte concentration, as well as interferences due to other ions. The calculated detection limit based on the variability of a blank solution (3s b criterion) for 10 measurements was 8.4 × 10 −8 mol L −1 , and the sensitivity determined from the slope of the calibration graph was 0.910 mol L −1 . The reproducibility (RSD) for five replicate measurements at 1.0 mg L −1 lead level was 1.6%. The results indicate that this electrode is sensitive and effective for the determination of Pb 2+ .

An electrochemical lead volatile species generation system, as a means for sample introduction into a flame atomic absorption spectrometer, has been developed and evaluated for the determination of lead in urine samples. The reaction cell, designed and manufactured in our laboratory, consists of a reaction compartment housing a reticulated glassy carbon cathode and a platinum wire anode. The cell can easily be coupled to the spectrometer via a gasliquid separator. The characteristic of the cathode material, the volatile species generation efficiency and the possible interferences of some concomitants have been studied. Calculated detection limit based on the variability of a blank solution (3 sb criterion) for ten measurements was 11 m gL 1 and the sensitivity determined from the slope of the calibration graph, was 0.152 L mg 1 . The reproducibility (RSD) for ten replicate measurements at 1.0 mg L 1 lead level, was 1.4 %. The accuracy of the method was determined through the analysis of spike urine samples. Recovery of 103.71 % 0.05 was achieved.

This report investigates the electrochemical behavior of hexacyanoferrate casted on Ni-Al2O3 modified electrodes and the preconcentration and detection of cesium ions on such films. It also studies the morphology and the composition of these surfaces. The film was grown on a glassy carbon (GC) surface. Five consecutive voltammetric cycles applied within 0.0 V and −1.6 V at a scan rate of 10 mV/s were enough to cast the film. Scanning electron microscopy (SEM) analyses showed a homogeneous, porous but broken surface of the film. Its composition was studied by X-ray diffraction (XRD). The presence of NiHCFe was confirmed by Fourier transformed infrared spectroscopy (FT-IR). The Cs+ preconcentration from diluted solutions was accomplished in 90 s, under a negative potential of −0.20 V applied to the modified working electrode. The detection of cesium has a good sensitivity and a wide linear interval (10−8 and 10−12 mol L−1). Even so, the limit of detection calculated was extremely low (2×10−16 mol L−1), cesium concentrations lower than 10−12 mol L−1 gave signals with no analytical significance. However, to our knowledge, this is the lowest level of cesium ever detected by an electroanalytical technique.

In this paper we describe the use of two kaolin-type aluminosilicate clays, a commercial ceramic-grade kaolin (K) and a natural kaolin from mines in Bolivar State Venezuela (K-Ve), for the preparation of film-based clay-modified glassy carbon electrodes. We examine their behavior during the preconcentration and subsequent anodic oxidation of 2-chlorophenol. Kaolin samples were used as raw materials and modified with cationic surfactant, cetyltrimethylammonium bromide (CTAB) or nonionic surfactant, octylphenoxypolyethoxyethanol (TX100). The electrode polishing was the key step to produce stable films. 2-Chlorophenol electrooxidation is favored by the presence of the surfactants in the film. The X-ray patterns show that the kaolin K-Ve includes quartz as nonclay mineral, while the kaolin K showed only diffraction peaks characteristic of kaolinite phase. This may be why the TX100/K-Ve/GC electrode adsorbs more 2-CPh than the TX100/K/GC electrode. On the other hand, analysis of the limiting currents obtained from hydrodynamic techniques indicated that the permeability of TX100/kaolin films is greater than that of CTAB/kaolin films. The TX100/K-Ve/GC electrode showed excellent stability. A linear response range from 0.01mgL−1 up to 0.1 mg L−1 with a detection limit of 0.0016 mg L−1 was observed in the optimized conditions.

The characteristics of hydrotalcite (HT)-like clay films containing ionic and nonionic surfactants and their ability to oxidize phenol have been examined. The HT clay (Co/Al-NO3) was synthesized by coprecipitation techniques and then modified with surfactants such as sodium dodecylbenzenesulfonate (SDBS), octylphenoxypolyethoxyethanol (TX100) or cetylpyridinium bromide (CPB). X-ray diffraction analysis revealed that the interlayer basal spacing varied depending on the type of surfactant retained by the HT. The presence of SDBS and CPB expanded the HT interlayer, which in the presence of TX100 did not show an appreciable change. Phenol oxidation is favored at surfactant-HT-GC modified electrodes, after a preconcentration time, compared to phenol oxidation at HT-GC or GC electrodes. Surfactant-HT-GC modified electrodes display good stability in continuous electrochemical phenol oxidation. At pH values between 6 and 10.8, both SDBS-HT-GC and TX100-HT-GC modified electrodes seem to be promising electrodes for the detection of phenol in water; while the CPB-HT-GC modified electrode should be affected by the inorganic anions.