Chemical speciation is defined as the distribution of an indi-vidual chemical element between dif... more Chemical speciation is defined as the distribution of an indi-vidual chemical element between different chemical species or groups of species [1]. In natural aquatic systems it reflects the chemical complexity of these media. Substan-tial progress has been made over recent years in chemical speciation and in the understanding of metal interactions with aquatic organisms, which are crucial issues owing to their intimate relationships with bioavailability and toxicity. In early studies, designed to measure trace metal toxicity, met-al solution chemistry was generally overlooked. However, more recent work has stressed the importance of metal solu-tion equilibria in controlling chemical speciation in the expo-sure medium external to organisms [1]. Metal complexation equilibria and speciation have been classical subjects of electroanalytical techniques, espe-cially potentiometry and voltammetry. In recent years, inter-est in this subject has been renewed because of the in-creasing focus ...
AhStlWt A general method is proposed for the investigation of metal-macromolecule interactions by... more AhStlWt A general method is proposed for the investigation of metal-macromolecule interactions by means of the voltammetric reduction of the metal ion in the presence of the macromolecule. The method considers two extreme cases: the absence or presence of electrodic adsorption. In the absence of electrodic adsorption, the method integrates some specific procedures previously developed to minimize the effects of variations in pH (and of other protolytic parameters) and adsorption of metals by cell components on the voltammetric response. A procedure for evaluating hydrodynamic conditions in anodic stripping voltammetry is also integrated in the data treatment. Some guidelines and procedures are given in order to account for the electrodic adsorption of the macromolecule and the induced adsorption of the metal ion. Either complexation and adsorption parameters or only complexation parameters can be estimated by means of a rigorous numerical or a semi-empirical method, respectively.
To evaluate plant response to Hg stress, glutathione, phytochelatins, and their Hg complexes were... more To evaluate plant response to Hg stress, glutathione, phytochelatins, and their Hg complexes were analyzed using HPLC with amperometric detection in samples of Asparagus acutifolius grown in the Almadeń mining district (Ciudad Real, Spain), one of the most Hg-contaminated sites in the world. Soils of the Almadeń mining district, and specifically from the Almadenejos zone, are highly contaminated, with some zones having values above 4,000 μg Hg g −1 soil. Although soils have an extremely high concentration of mercury, generally less than 2% is available for plants, as is shown by various soil extractions simulating bioavailability. In plants, Hg concentration increases depending on the content of Hg in soils. In addition, Hg levels in roots are higher than in aerial parts, which is a strategy of plants for protecting their more sensitive aerial parts from the deleterious effects of metal stress. The total content of phytochelatins (PCs) and their complexes are directly related with the amount of mercury in soils. These findings highlight the important role of thiol compounds and their metal complexes in capturing and fixing Hg from soils, giving plants the capacity to deal with the heavy metal toxicity of polluted soils.
En la investigacio de la complexacio de metalls mitjancant eines electroanalitiques son emprades ... more En la investigacio de la complexacio de metalls mitjancant eines electroanalitiques son emprades dues aproximacions generals. La primera, anomenada de modelatge dur (hardmodelling), es basa en la formulacio d'un model fisicoquimic conjunt per als processos electrodic i de complexacio i en la resolucio analitica o numerica del model. Posteriorment, l'ajust dels parametres del model a les dades experimentals donara la informacio desitjada sobre el proces de complexacio. La segona aproximacio, anomenada de modelatge tou (soft-modelling), es basa en la identificacio d'un model de complexacio a partir de l'analisi numerica i estadistica de les dades, sense cap assumpcio previa d'un model. Aquesta aproximacio, que ha estat extensivament emprada amb dades espectroscopiques, ho ha estat poquissim amb dades electroquimiques. En aquest article tractem de la formulacio d'un model (hard-modelling) per a la complexacio de metalls en sistemes amb mescles de lligands, inclo...
For a long time mercury electrodes have been the main choice for the analysis of metal ions and s... more For a long time mercury electrodes have been the main choice for the analysis of metal ions and some metalloids. However, in the last years, safety and environmental considerations have restricted their use and encouraged the search for alternative materials more environmentally friendly and with more possibilities for in-situ and flow analysis. This research has been reinforced by the popularisation of nanomaterials, biomolecules and screen-printed electrodes, as well as for the new advances in sensor miniaturization and integration of the electrodes in multi-sensor platforms and electronic tongues. The present review critically summarizes and discusses the progress made since 2010 in the development and application of new electrodes for the analysis of metals and metalloids.
A novel selenium based screen-printed electrode was developed based on the immobilization of sele... more A novel selenium based screen-printed electrode was developed based on the immobilization of selenocystine on aryl diazonium salt monolayers anchored to a carbon-nanofiber screen-printed electrode support (SeCyst-SPCNFE). SeCyst-SPCNFE was analytically compared to a screen-printed carbon nanofiber electrode modified with L-Cystine (Cyst-SPCNFE) for the determination of Pb(II) and Cd(II) by stripping voltammetric techniques. Their analytical performance suggests that SeCyst-SPCNFE could be a much better alternative for metal ion determination at trace levels than Cyst-SPCNFE. The proposed electrode was successfully applied for the simultaneous voltammetric determination of trace Pb(II) and Cd(II) in a wastewater reference material with a very high reproducibility (3.2 %) and good trueness (2.6 %).
The use of an antimony film coated on a screen-printed carbon electrode (ex-situ SbSPCE) is propo... more The use of an antimony film coated on a screen-printed carbon electrode (ex-situ SbSPCE) is proposed for the determination of Pd(II) at ppb levels in natural samples by adsorptive stripping voltammetry using dimethylglyoxime as chelating agent. Ex-situ SbSPCE produces a better analytical performance as compared to a commercially sputtered bismuth screen-printed electrode (BispSPE). The detection and quantification limits were 2.7 and 9.0µgL(-1) respectively with a good linear behaviour in the wide examined concentration range (from 1µgL(-1) up to 100.0µgL(-1), R(2)=0.998). The proposed ex-situ SbSPCE showed an excellent repeatability with a relative standard deviation of 0.5% for ten successive measurements and a very good reproducibility (1.6% for three different ex-situ SbSPCE units within series of ten repetitive assays). Moreover, the ex-situ SbSPCE was successfully applied for the determination of low concentration levels of Pd(II) in spiked tap water with a very high reproduci...
The effects of mercury (Hg) released from a chlor-alkali factory in aquatic plants along the Ebro... more The effects of mercury (Hg) released from a chlor-alkali factory in aquatic plants along the Ebro River basin (NE Spain) were analysed considering the phytochelatins (PCn) and their isoforms content in these plants. These compounds were analyzed using HPLC with amperometric detection, and the macrophytes species Ceratophyllum demersum and Myriopyllum spicatum were collected in two sampling campaigns, autumn and spring, respectively. To correlate the PCn content in macrophytes with the Hg contamination, analysis of total Hg (THg) content in plants and suspended particulate matter, as well as the dissolved-bioavailable fraction of Hg in water measured by the diffusive gradient in thin film (DGT) technique were done. The results confirm the presence of PC2-Ala in extracts of C. demersum and PC2-desGly in M. spicatum, and the concentration of these thiol compounds depends clearly on the distance between the hot spot and the downstream sites: the higher the levels are, the closer the hot...
Different techniques for factor analysis (FA) have been applied in the study of weak consecutive ... more Different techniques for factor analysis (FA) have been applied in the study of weak consecutive complexes of Cd(I1) propanoate by analysing experimental matrices obtained from four electroanalytical techniques: normal pulse polarography (NPP), reverse normal pulse polarography (RNPP), differential pulse polarography (DPP) and differential pulse anodic stripping voltammetry (DPASV). All experiments were performed at a constant temperature, 25fl"C, in aqueous solutions having a constant cadmium ion concentration (10 and 20 PM), varying propanoate concentrations in the range 10400 mM, a constant c(propanoic acid)-to-c(sodium propanoate) ratio (1 : 50), and a constant ionic strength (2 M), obtained by addition of NaC104. From the experimental signals using DeFord and Hume's model, to calculate the experimental F. function model identification, pi estimates and corresponding standard error of stability constants were obtained using conventional fitting of polynomial (univariate hard modelling) to the experimental data, together with the recently proposed evolving polynomial fitting and optimized least squares extrapolation of Fi functions. The same experimental data matrices were analysed by multivariate soft modelling approach using the following FA techniques: principal component analysis (PCA), evolving factor analysis (EFA) and constrained alternating least squares (ALS) optimization of individual and global (augmented) data matrices.
The determination of Sb(III) on an ex-situ bismuth screen-printed carbon electrode (ex-situ BiSPC... more The determination of Sb(III) on an ex-situ bismuth screen-printed carbon electrode (ex-situ BiSPCE) by means of adsorptive stripping voltammetry (AdSV) using quercetin-5'-sulfonic acid as chelating agent was optimized. The effect of different experimental parameters such pH, ligand concentration (CQSA), accumulation potential (Eacc) and accumulation time (tacc) were studied to obtain a wide linear range, the highest sensitivity and the lowest detection limit. Ex-situ BiSPCE was analytically compared with a sputtered bismuth screen-printed electrode (BispSPE) under optimal conditions. The obtained analytical parameters suggest that ex-situ BiSPCE behaves much better than BispSPE and the first was selected for this study. Optimal parameters were pH=4.6; CQSA=10.0 to 20.0×10(-6)molL(-1); Eacc=-0.5V and tacc=60s. Peak area is proportional to Sb(III) concentration up to 100.0μgL(-1) (tacc 60s) and 45.0μgL(-1) (tacc 120s) range, with detection limits of 1.2μgL(-)(1) (tacc 60s) and 0.8...
Three different commercial carbon nanomaterial-modified screen-printed electrodes based on graphe... more Three different commercial carbon nanomaterial-modified screen-printed electrodes based on graphene, carbon nanotubes and carbon nanofibers were pioneeringly tested as electrode platforms for the plating with Sb film. They were microscopically and analytically compared to each other and to the most conventional unmodified carbon screen-printed electrode (SPCE). The obtained detection and quantification limits suggest that the in-situ antimony film electrode prepared from carbon nanofibers modified screen-printed electrode (SbSPCE-CNF) produces a better analytical performance as compared to the classical SPCE modified with antimony for Pb(II) and Cd(II) determination, approving its appropriateness for measuring low μg L(-1) levels of the considered metals. In-situ SbSPCE-CNF was successfully used for the simultaneous determination of Pb(II) and Cd(II) ions, by means of differential pulse anodic stripping voltammetry, in a certified reference estuarine water sample with a very high re...
This work reports the development of a glutathione modified electrode via electrografting on a sc... more This work reports the development of a glutathione modified electrode via electrografting on a screen-printed carbon nanofiber substrate (GSH-SPCNFE). GSH-SPCNFE was compared to a classical screenprinted carbon electrode modified with glutathione (GSH-SPCE) for the simultaneous voltammetric determination of Cd(II) and Pb(II). Their electrochemical characterization and analytical performance suggest that SPCNFE could be a much better support for GSH immobilization. The applicability of GSH-SPCNFE for the determination of low concentration levels of Pb(II) and Cd(II) ions in environmental samples was successfully tested in a certified wastewater reference material by means of stripping voltammetry with a very high reproducibility and good trueness.
Chemical speciation is defined as the distribution of an indi-vidual chemical element between dif... more Chemical speciation is defined as the distribution of an indi-vidual chemical element between different chemical species or groups of species [1]. In natural aquatic systems it reflects the chemical complexity of these media. Substan-tial progress has been made over recent years in chemical speciation and in the understanding of metal interactions with aquatic organisms, which are crucial issues owing to their intimate relationships with bioavailability and toxicity. In early studies, designed to measure trace metal toxicity, met-al solution chemistry was generally overlooked. However, more recent work has stressed the importance of metal solu-tion equilibria in controlling chemical speciation in the expo-sure medium external to organisms [1]. Metal complexation equilibria and speciation have been classical subjects of electroanalytical techniques, espe-cially potentiometry and voltammetry. In recent years, inter-est in this subject has been renewed because of the in-creasing focus ...
AhStlWt A general method is proposed for the investigation of metal-macromolecule interactions by... more AhStlWt A general method is proposed for the investigation of metal-macromolecule interactions by means of the voltammetric reduction of the metal ion in the presence of the macromolecule. The method considers two extreme cases: the absence or presence of electrodic adsorption. In the absence of electrodic adsorption, the method integrates some specific procedures previously developed to minimize the effects of variations in pH (and of other protolytic parameters) and adsorption of metals by cell components on the voltammetric response. A procedure for evaluating hydrodynamic conditions in anodic stripping voltammetry is also integrated in the data treatment. Some guidelines and procedures are given in order to account for the electrodic adsorption of the macromolecule and the induced adsorption of the metal ion. Either complexation and adsorption parameters or only complexation parameters can be estimated by means of a rigorous numerical or a semi-empirical method, respectively.
To evaluate plant response to Hg stress, glutathione, phytochelatins, and their Hg complexes were... more To evaluate plant response to Hg stress, glutathione, phytochelatins, and their Hg complexes were analyzed using HPLC with amperometric detection in samples of Asparagus acutifolius grown in the Almadeń mining district (Ciudad Real, Spain), one of the most Hg-contaminated sites in the world. Soils of the Almadeń mining district, and specifically from the Almadenejos zone, are highly contaminated, with some zones having values above 4,000 μg Hg g −1 soil. Although soils have an extremely high concentration of mercury, generally less than 2% is available for plants, as is shown by various soil extractions simulating bioavailability. In plants, Hg concentration increases depending on the content of Hg in soils. In addition, Hg levels in roots are higher than in aerial parts, which is a strategy of plants for protecting their more sensitive aerial parts from the deleterious effects of metal stress. The total content of phytochelatins (PCs) and their complexes are directly related with the amount of mercury in soils. These findings highlight the important role of thiol compounds and their metal complexes in capturing and fixing Hg from soils, giving plants the capacity to deal with the heavy metal toxicity of polluted soils.
En la investigacio de la complexacio de metalls mitjancant eines electroanalitiques son emprades ... more En la investigacio de la complexacio de metalls mitjancant eines electroanalitiques son emprades dues aproximacions generals. La primera, anomenada de modelatge dur (hardmodelling), es basa en la formulacio d'un model fisicoquimic conjunt per als processos electrodic i de complexacio i en la resolucio analitica o numerica del model. Posteriorment, l'ajust dels parametres del model a les dades experimentals donara la informacio desitjada sobre el proces de complexacio. La segona aproximacio, anomenada de modelatge tou (soft-modelling), es basa en la identificacio d'un model de complexacio a partir de l'analisi numerica i estadistica de les dades, sense cap assumpcio previa d'un model. Aquesta aproximacio, que ha estat extensivament emprada amb dades espectroscopiques, ho ha estat poquissim amb dades electroquimiques. En aquest article tractem de la formulacio d'un model (hard-modelling) per a la complexacio de metalls en sistemes amb mescles de lligands, inclo...
For a long time mercury electrodes have been the main choice for the analysis of metal ions and s... more For a long time mercury electrodes have been the main choice for the analysis of metal ions and some metalloids. However, in the last years, safety and environmental considerations have restricted their use and encouraged the search for alternative materials more environmentally friendly and with more possibilities for in-situ and flow analysis. This research has been reinforced by the popularisation of nanomaterials, biomolecules and screen-printed electrodes, as well as for the new advances in sensor miniaturization and integration of the electrodes in multi-sensor platforms and electronic tongues. The present review critically summarizes and discusses the progress made since 2010 in the development and application of new electrodes for the analysis of metals and metalloids.
A novel selenium based screen-printed electrode was developed based on the immobilization of sele... more A novel selenium based screen-printed electrode was developed based on the immobilization of selenocystine on aryl diazonium salt monolayers anchored to a carbon-nanofiber screen-printed electrode support (SeCyst-SPCNFE). SeCyst-SPCNFE was analytically compared to a screen-printed carbon nanofiber electrode modified with L-Cystine (Cyst-SPCNFE) for the determination of Pb(II) and Cd(II) by stripping voltammetric techniques. Their analytical performance suggests that SeCyst-SPCNFE could be a much better alternative for metal ion determination at trace levels than Cyst-SPCNFE. The proposed electrode was successfully applied for the simultaneous voltammetric determination of trace Pb(II) and Cd(II) in a wastewater reference material with a very high reproducibility (3.2 %) and good trueness (2.6 %).
The use of an antimony film coated on a screen-printed carbon electrode (ex-situ SbSPCE) is propo... more The use of an antimony film coated on a screen-printed carbon electrode (ex-situ SbSPCE) is proposed for the determination of Pd(II) at ppb levels in natural samples by adsorptive stripping voltammetry using dimethylglyoxime as chelating agent. Ex-situ SbSPCE produces a better analytical performance as compared to a commercially sputtered bismuth screen-printed electrode (BispSPE). The detection and quantification limits were 2.7 and 9.0µgL(-1) respectively with a good linear behaviour in the wide examined concentration range (from 1µgL(-1) up to 100.0µgL(-1), R(2)=0.998). The proposed ex-situ SbSPCE showed an excellent repeatability with a relative standard deviation of 0.5% for ten successive measurements and a very good reproducibility (1.6% for three different ex-situ SbSPCE units within series of ten repetitive assays). Moreover, the ex-situ SbSPCE was successfully applied for the determination of low concentration levels of Pd(II) in spiked tap water with a very high reproduci...
The effects of mercury (Hg) released from a chlor-alkali factory in aquatic plants along the Ebro... more The effects of mercury (Hg) released from a chlor-alkali factory in aquatic plants along the Ebro River basin (NE Spain) were analysed considering the phytochelatins (PCn) and their isoforms content in these plants. These compounds were analyzed using HPLC with amperometric detection, and the macrophytes species Ceratophyllum demersum and Myriopyllum spicatum were collected in two sampling campaigns, autumn and spring, respectively. To correlate the PCn content in macrophytes with the Hg contamination, analysis of total Hg (THg) content in plants and suspended particulate matter, as well as the dissolved-bioavailable fraction of Hg in water measured by the diffusive gradient in thin film (DGT) technique were done. The results confirm the presence of PC2-Ala in extracts of C. demersum and PC2-desGly in M. spicatum, and the concentration of these thiol compounds depends clearly on the distance between the hot spot and the downstream sites: the higher the levels are, the closer the hot...
Different techniques for factor analysis (FA) have been applied in the study of weak consecutive ... more Different techniques for factor analysis (FA) have been applied in the study of weak consecutive complexes of Cd(I1) propanoate by analysing experimental matrices obtained from four electroanalytical techniques: normal pulse polarography (NPP), reverse normal pulse polarography (RNPP), differential pulse polarography (DPP) and differential pulse anodic stripping voltammetry (DPASV). All experiments were performed at a constant temperature, 25fl"C, in aqueous solutions having a constant cadmium ion concentration (10 and 20 PM), varying propanoate concentrations in the range 10400 mM, a constant c(propanoic acid)-to-c(sodium propanoate) ratio (1 : 50), and a constant ionic strength (2 M), obtained by addition of NaC104. From the experimental signals using DeFord and Hume's model, to calculate the experimental F. function model identification, pi estimates and corresponding standard error of stability constants were obtained using conventional fitting of polynomial (univariate hard modelling) to the experimental data, together with the recently proposed evolving polynomial fitting and optimized least squares extrapolation of Fi functions. The same experimental data matrices were analysed by multivariate soft modelling approach using the following FA techniques: principal component analysis (PCA), evolving factor analysis (EFA) and constrained alternating least squares (ALS) optimization of individual and global (augmented) data matrices.
The determination of Sb(III) on an ex-situ bismuth screen-printed carbon electrode (ex-situ BiSPC... more The determination of Sb(III) on an ex-situ bismuth screen-printed carbon electrode (ex-situ BiSPCE) by means of adsorptive stripping voltammetry (AdSV) using quercetin-5'-sulfonic acid as chelating agent was optimized. The effect of different experimental parameters such pH, ligand concentration (CQSA), accumulation potential (Eacc) and accumulation time (tacc) were studied to obtain a wide linear range, the highest sensitivity and the lowest detection limit. Ex-situ BiSPCE was analytically compared with a sputtered bismuth screen-printed electrode (BispSPE) under optimal conditions. The obtained analytical parameters suggest that ex-situ BiSPCE behaves much better than BispSPE and the first was selected for this study. Optimal parameters were pH=4.6; CQSA=10.0 to 20.0×10(-6)molL(-1); Eacc=-0.5V and tacc=60s. Peak area is proportional to Sb(III) concentration up to 100.0μgL(-1) (tacc 60s) and 45.0μgL(-1) (tacc 120s) range, with detection limits of 1.2μgL(-)(1) (tacc 60s) and 0.8...
Three different commercial carbon nanomaterial-modified screen-printed electrodes based on graphe... more Three different commercial carbon nanomaterial-modified screen-printed electrodes based on graphene, carbon nanotubes and carbon nanofibers were pioneeringly tested as electrode platforms for the plating with Sb film. They were microscopically and analytically compared to each other and to the most conventional unmodified carbon screen-printed electrode (SPCE). The obtained detection and quantification limits suggest that the in-situ antimony film electrode prepared from carbon nanofibers modified screen-printed electrode (SbSPCE-CNF) produces a better analytical performance as compared to the classical SPCE modified with antimony for Pb(II) and Cd(II) determination, approving its appropriateness for measuring low μg L(-1) levels of the considered metals. In-situ SbSPCE-CNF was successfully used for the simultaneous determination of Pb(II) and Cd(II) ions, by means of differential pulse anodic stripping voltammetry, in a certified reference estuarine water sample with a very high re...
This work reports the development of a glutathione modified electrode via electrografting on a sc... more This work reports the development of a glutathione modified electrode via electrografting on a screen-printed carbon nanofiber substrate (GSH-SPCNFE). GSH-SPCNFE was compared to a classical screenprinted carbon electrode modified with glutathione (GSH-SPCE) for the simultaneous voltammetric determination of Cd(II) and Pb(II). Their electrochemical characterization and analytical performance suggest that SPCNFE could be a much better support for GSH immobilization. The applicability of GSH-SPCNFE for the determination of low concentration levels of Pb(II) and Cd(II) ions in environmental samples was successfully tested in a certified wastewater reference material by means of stripping voltammetry with a very high reproducibility and good trueness.
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Papers by Miquel Esteban