Gorka Arana | University of the Basque Country, Euskal Herriko Unibertsitatea (original) (raw)

Papers by Gorka Arana

Research paper thumbnail of Potentiometric determination of the protonation constants of some phenols in 1.0 mol/L NaCl at 25°C

Fresenius Journal of Analytical Chemistry, 1994

The potentiometric determination of the protonation constants of phenol, 2-chlorophenol, 2-nitrop... more The potentiometric determination of the protonation constants of phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol and 2-methylphenol in 1.0 mol/L NaCl at 25°C is presented. An automated system has been used in the experiments. The determination of the constants has been carried out using both graphical and numerical methods.

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Research paper thumbnail of Potentiometric study of the distribution equilibria of phenols between 1.0 moldm −3 NaCl and organic solvents at 25 °C

Mikrochimica Acta, 1994

The potentiometric determination of the distribution coefficient of phenol, 2-chlorophenol, 2-nit... more The potentiometric determination of the distribution coefficient of phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol and 2-methyl-phenol between 1.0 mol dm−3 NaCl and five different organic solvents at 25 °C is presented. An automated potentiometric system was used and the determination of the constants was carried out using both graphical and numerical methods. The relevance of this study for the development of supported liquid membrane (SLM) recovery systems is discussed.

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Research paper thumbnail of Bronze analysis by k 0 NAA and PIXE

Journal of Radioanalytical and Nuclear Chemistry, 2003

Five copper alloys were prepared with modern powder metallurgical processes in the frame of the E... more Five copper alloys were prepared with modern powder metallurgical processes in the frame of the European project ‘Improvement of Means of Measurement on Archaeological Copper-Alloys for Characterisation and Conservation (IMMACO)’ and certified for As, Pb, Sn and Zn mass fractions. Similar in their composition to archaeological bronze alloys, these Certified Reference Materials (CRMs) are to be used for calibration of XRF instruments for characterization of archaeological samples either in the laboratory or in the field. This paper presents and compares the successful contribution of our non-destructive analytical methods (k 0-NAA and PIXE) to the IMMACO project and to the certification of the five reference materials.

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Research paper thumbnail of On-Line Multicomponent Determination of the Flux of Mixtures of Phenols Through a Liquid Membrane in Real Time

Mikrochimica Acta, 2001

The analysis of mixtures of four phenolic compounds in an on-line system using UV-visible measur... more The analysis of mixtures of four phenolic compounds in an on-line system using UV-visible measurements with a fibre optic probe is discussed in this work. The aim of this system is to provide accurate real time concentration profiles in order to monitor the transport of phenols across a solid supported liquid membrane in both the feed and stripping phases. Different calibration models are taking into account the pH of the solution, using experimental designs and the first derivative in combination with different multivariate approaches like multiple linear regression (MLR), inverted least squares (ILS) and partial least squares regression (PLS). The comparison of all these combinations is carried out by means of the predictive residual error sum of squares (PRESS) evaluated from an independent set of spectra. From this comparison it is concluded that a PLS model using first derivative spectra offers the most accurate and robust prediction in the permeation experiments. Additionally, the stability of the model and the figures of merit obtained are also discussed.

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Research paper thumbnail of Potentiometric study of the protonation and distribution equilibria of 2-chlorophenol in NaCl medium at 25 °C. Construction of a thermodynamic model

Talanta, 1996

The potentiometric determination of the protonation constant of 2-chlorophenol in NaCl media at d... more The potentiometric determination of the protonation constant of 2-chlorophenol in NaCl media at different ionic strengths and its distribution coefficient between these media and two organic solvents at 25 °C are presented. An automated potentiometric system was used, and the determination of the constants was carried out using both graphical and numerical methods. A thermodynamic model using the modified Bromley methodology has been constructed for the prediction of protonation constants and distribution coefficients in NaCl media. The relevance of this study to the development of supported liquid membrane recovery systems is discussed.

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Research paper thumbnail of Is It Safe to Use Poisson Statistics in Nuclear Spectrometry?

Journal of Radioanalytical and Nuclear Chemistry, 2000

The boundary conditions in which Poisson statistics can be applied in nuclear spectrometry are in... more The boundary conditions in which Poisson statistics can be applied in nuclear spectrometry are investigated. Improved formulas for the uncertainty of nuclear counting with deadtime and pulse pileup are presented. A comparison is made between the expected statistical uncertainty for loss-free counting, fixed live-time and fixed real-time measurements.

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Research paper thumbnail of Classification of archaeological pieces into their respective stratum by a chemometric model based on the soil concentration of 25 selected elements

Spectrochimica Acta Part B-atomic Spectroscopy, 2010

The aim of this work was to demonstrate that an archaeological ceramic piece has remained buried ... more The aim of this work was to demonstrate that an archaeological ceramic piece has remained buried underground in the same stratum for centuries without being removed. For this purpose, a chemometric model based on Principal Component Analysis, Soft Independent Modelling of Class Analogy and Linear Discriminant Analysis classification techniques was created with the concentration of some selected elements of both soil of the stratum and soil adhered to the ceramic piece. Some ceramic pieces from four different stratigraphic units, coming from a roman archaeological site in Alava (North of Spain), and its respective stratum soils were collected. The soil adhered to the ceramic pieces was removed and treated in the same way as the soil from its respective stratum. The digestion was carried out following the US Environmental Pollution Agency EPA 3051A method. A total of 54 elements were determined in the extracts by a rapid screening inductively coupled plasma mass spectrometry method. After rejecting the major elements and those which could have changed from the original composition of the soils (migration or retention from/to the buried objects), the following elements (25) were finally taken into account to construct the model: Li, V, Co, As, Y, Nb, Sn, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Au, Th and U. A total of 33 subsamples were treated from 10 soils belonging to 4 different stratigraphic units. The final model groups and discriminate them in four groups, according to the stratigraphic unit, having both the stratum and soils adhered to the pieces falling down in the same group.

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Research paper thumbnail of Calcium inhibits diacylglycerol uptake by serum albumin

Biochimica Et Biophysica Acta-biomembranes, 2009

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Research paper thumbnail of Pattern recognition and classification of sediments according to their metal content using chemometric tools. A case study: The estuary of Nerbioi-Ibaizabal River (Bilbao, Basque Country)

Chemosphere, 2011

Chemometrics are increasingly used in environmental monitoring studies, but are still far from be... more Chemometrics are increasingly used in environmental monitoring studies, but are still far from being accepted as routine tools by field specialists. The multivariate character of usually highly correlated environmental data recommends the use of advanced chemometrics as part of the analytical methodology in order to get information on the basic structure of data. In this work, we have applied a battery of non-supervised (Principal Component Analysis (PCA)) and supervised (k-Nearest Neighbour (k-NN), Soft Independent Modelling of Class Analogies (SIMCA), Linear Discriminant Analysis (LDA) and Artificial Neural Networks (ANNs)) multivariate techniques on a specific environmental dataset. The dataset consists on the concentration of 14 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn) in 95 sediments collected at eight different locations of the estuary of the Nerbioi-Ibaizabal River (Bilbao, Basque Country) during 12 sampling campaigns conducted every 3 months between 2005 and 2008. The study aims to present a simple methodology of general applicability which may result in a flexible and practical tool to assess chemical pollution in sediments of a given specific site.► Long-term monitoring of pollution in the estuary of the Nerbioi-Ibaizabal River. ► Sediments as indicators of metal pollution in estuaries. ► Combination of chemometric techniques for pattern recognition and classification. ► Chemometric classification of sediments according to their metal content.

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Research paper thumbnail of Multisimplex Optimisation of the Purge-and-Trap Preconcentration of Volatile Fatty Acids, Phenols and Indoles in Cow Slurries

Chromatographia, 2008

In this work the simultaneous purge-and-trap (P&T) preconcentration of volatile fatty acids (acet... more In this work the simultaneous purge-and-trap (P&T) preconcentration of volatile fatty acids (acetic acid, propanoic acid, butanoic acid, iso-butanoic acid, pentanoic acid, iso-pentanoic acid, hexanoic acid and heptanoic acid), phenols (phenol, 4-methylphenol and 4-ethylphenol) and indoles (indole and 3-methylindole) from cow slurries was carried out in order to quantify them by gas chromatography flame ionisation detection (GC–FID). The optimisation of the preconcentration was performed using spiked cow slurries and the variables studied were the nature of the trap, the purge and heating time and the amount of inert salt (NaCl) added. Other parameters such as purge flow, sample volume, desorption time and temperature and baking time and temperature were kept constant. The first variable studied was the nature of the preconcentration trap. Four different commercially available traps (Vocarb 4000, Vocarb 3000, BTEXTRAP and Tenax/silica gel/carbon) were studied and Vocarb 3000 gave best results. Once the optimum trap was chosen, appearance of possible memory peaks were studied and significant signals were observed for 4-methylphenol, 4-ethylphenol, indole and 3-methylindole. In order to improve the blanks after each analysis the following actions were taken: (1) the needle sparger was located in the headspace of the sample and (2) all the replaceable parts of the P&T (sample tube, needle sparger, Teflon ferrules, nuts, etc.) were washed, sonicated in acetone for 15 min and dried in an oven at 350 °C. Once the blank problems were minimised, the remaining variables (purge and heating time and the amount of NaCl) were optimised using the MultiSimplex® program, which enabled the study of several variables and responses simultaneously. Optimum conditions for the simultaneous preconcentration were obtained after 24 experiments and the final optimised preconcentration conditions were as follows: 0.4 g of NaCl were added to 10 mL sample which was heated at 80 °C for 10 min and purged for 20 min while the Vocarb 3000 trap remained at room temperature. Once the purge step was over, the trap was desorbed at 250 °C for 6 min and baked at 260 °C for 10 min. After the optimisation of the P&T based preconcentration, the precision (within and among days), accuracy and detection limits of the method were studied.

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Research paper thumbnail of Spectroscopic evaluation of the environmental impact on black crusted modern mortars in urban–industrial areas

Analytical and Bioanalytical Chemistry, 2011

A multianalytical characterisation of black crusted modern construction materials from buildings ... more A multianalytical characterisation of black crusted modern construction materials from buildings located in the Bilbao Metropolitan area (North Spain) was carried out. According to the mineral composition determined by Raman spectroscopy, calcite and hematite were the major compounds found while aragonite, limonite, rutile, quartz and some aluminosilicates such as obsidian or amazonite (KAlSi3O8) were also present in minor percentages. As deterioration products, gypsum and anhydrite were widely found not only in the surface but also in the inner part of strongly deteriorated samples. Coquimbite (Fe2(SO4)3·9H2O) was identified as well in the most protected facade where high amounts of Fe, having probably an anthropogenic origin, were measured by micro X-ray fluorescence (μ-XRF). Zn was found to be in high amounts while Cu, Pb, Ti, Mn, Sr and K were identified as minor elements. Considering the non-expected concentrations found for some anthropogenic elements, a sequential extraction was carried out in order to determine their chemical form by means of ion chromatography and inductively coupled plasma mass spectrometry. The orientation of the facades, which had a different influence from rain washing and industrial and traffic impact, was shown to affect the accumulation of different compounds in the black crust. Finally, the MEDUSA software was used to simulate the reactions among the original compounds, deposited pollutants and the atmospheric acid gases in order to explain the presence of the decaying species found. Figure Multianalytical Speciation protocol applied on the analysis of modern mortars

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Research paper thumbnail of Selenium in electrolytic manganese as a reference material for the quality control of aluminium melts

Accreditation and Quality Assurance, 2007

Electrolytic manganese is an important alloying element for aluminium and steel melts. It is main... more Electrolytic manganese is an important alloying element for aluminium and steel melts. It is mainly added to melts of aluminium in the holding furnace as tablets or minitablets (compressed compacts of manganese and aluminium powders). Selenium derivates are usually added during the production of electrolytic manganese, so some selenium is present in the alloys produced when electrolytic manganese is added to the aluminium furnace. Since the selenium contents of many alloys are of concern from health and environmental perspectives, their values should be provided. In this work, a laboratory reference material (LRM) based on electrolytic manganese was produced to assure our routine quality control method, where selenium is analysed by hydride generation followed by optical emission spectrometry with inductively coupled plasma (HG–ICP–OES). Therefore, the present paper describes in detail the preparation procedure for and the results from homogeneity and stability studies performed on electrolytic manganese LRM. For this purpose, a commercial electrolytic manganese lot was selected and the main factors involved in the preparation of the material (pretreatment step, homogenization, bottling and storage) were carefully studied and established in order to guarantee the long-term stability of the LRM. The results obtained showed that the LRM developed was a fit-for-purpose material for the quality control of the routine analysis of selenium.

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Research paper thumbnail of Diagnosing the Impact of Traffic on Roadside Soils Through Chemometric Analysis on the Concentrations of More Than 60 Metals Measured by ICP/MS

This study aims to establish the impact of traffic pollution at two parallel roads in the provinc... more This study aims to establish the impact of traffic pollution at two parallel roads in the province of Biscay (North of Spain). Soil samples digestions were carried out following the EPA 3051A method and the extracts were analyzed by ICP/MS. A rapid screening method for the determination of more than 60 metals is proposed. The subsequent chemometric treatment of the obtained data shows the presence of more than ten traffic related metals: Cd, Cr, Cu, Hf, Mo, Nb, Ni, Pb, Sb, Sn, Sr, Zn and Zr. Different soil types (in the old road and in the highway) can be distinguished by means of its rare earth and alkaline metal concentration. Very high concentrations of Zn were found in soil under the guard rail.

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Research paper thumbnail of The effect of the nature of the polymer backbone on the stability and the analytical response of polymer-modified electrodes

Electroanalysis, 1995

The synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)2(PS)... more The synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)2(PS)7.5(DMAP)2.5Cl]Cl, where bipy = 2,2′-bipyridyl, PS = polystyrene, and DMAP = poly[4-(N-methyl-N-p-vinylbenzylamino) pyridine], are described. The charge transport properties of electrodes modified with the redox material are investigated using cyclic voltammetry and chronoamperometry. The modified electrode behaves as an efficient electrocatalyst for the outer-sphere reduction of FeIII, with the cross-exchange reaction occurring at the surface of the polymer (Sk″) at concentrations less than 1.0 × 10−3 mol dm−3 FeIII, with a change over to the Ste, kinetic regime at higher substrate concentrations. Direct agreement was observed between the kinetic behavior at rotating disk electrodes and in thin-layer flow cells. Application of the modified electrodes for the determination of iron in pharmaceutical formulations and the long term stability of the electrodes are investigated. The results obtained are compared with those reported for the analogous metallopolymer [Os(bipy)2(PVP)10Cl]Cl, where PVP is poly-4-vinylpyridine.

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Research paper thumbnail of Hydrolysis of Nb(V) and Ta(V) in aqueous KCl at 25°C. Part II: Construction of a thermodynamic model for Ta(V)

Journal of Solution Chemistry, 1995

In this work the hydrolysis of Ta(V) in 3.0M KCl has been studied by measuring the H3O+ ion conce... more In this work the hydrolysis of Ta(V) in 3.0M KCl has been studied by measuring the H3O+ ion concentration with a glass electrode. The experimental work consisted of automatically controlled potentiometric titrations. The results were treated using graphical and numerical methods and, as a result, the hydrolysis process can be considered as a homonuclear protolysis. Finally, the results obtained were compared with other data found in the literature and a hydrolysis model for Ta(V) was built by means of the modified Bromley theory.

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Research paper thumbnail of Headspace-solid-phase microextraction preconcentration of phenols, indoles and on-fibre derivatised volatile fatty acids in liquid and gas samples from cow slurries

Journal of Separation Science, 2007

Odorous organic compounds from liquid and gas samples of animal wastes were studied by headspace ... more Odorous organic compounds from liquid and gas samples of animal wastes were studied by headspace (HS)-solid-phase microextraction (SPME)-GC-MS. 1-Pirenyldiazomethane (PDAM) was adsorbed/absorbed on the SPME fibre in order to obtain the corresponding ester derivatives during the preconcentration step. The SPME fibre was immersed into a PDAM solution. Then, the SPME fibre was withdrawn and exposed to the HS of the liquid cow slurry. This way derivatisation of VFAs took place in the SPME fibre together with the preconcentration of the rest of the analytes of interest. The analytes were desorbed in the hot injection port (300°C) of a GC-MS for 3 min. Four different fibre types and different immersion periods of the fibre in the PDAM solution were studied in order to obtain the best sensitivity with the selected fibre. Accuracy, precision and the LODs were calculated using spiked liquid and gas samples. The possibility of storing liquid samples after sampling by preconcentration on the fibre was also considered. Storage time and temperature were studied. The optimised method was applied to the determination of the analytes in liquid and gas samples from cow slurries from an intensive production farm.

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Research paper thumbnail of Risk assessment of trace elements in sediments: The case of the estuary of the Nerbioi–Ibaizabal River (Basque Country)

Journal of Hazardous Materials, 2010

Long term (January 2005–January 2008) monitoring of sediments was used to investigate metal pollu... more Long term (January 2005–January 2008) monitoring of sediments was used to investigate metal pollution in the estuary of the Nerbioi–Ibaizabal River (Bilbao, Basque Country). Sediments were collected from eight representative locations of the estuary approximately every three months. The concentration of fourteen elements was measured in sediment extracts. Different graphical representations of the data set, simple statistical methods and sediment quality guidelines were combined to investigate trends in space and time, identify pollution sources, and assess sediment quality from a toxicological point of view. In general terms, the main trend reveals a significant fall in metal concentration over the period investigated. There are still certain points of the estuary with relatively high concentration of toxic metals, but the toxicological approach suggests that the risk for living organisms is not important.

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Research paper thumbnail of Preparation of a reference mussel tissue material for polycyclic aromatic hydrocarbons and trace metals determination

Analytica Chimica Acta, 2010

Due to high cost of certified reference materials (CRMs), reference materials (RMs) are preferred... more Due to high cost of certified reference materials (CRMs), reference materials (RMs) are preferred to check the method performance in environmental analysis. In this work, a laboratory reference material (LRM) was prepared and characterised to carry out the quality control in monitoring analysis of eight polycyclic aromatic hydrocarbons (PAHs) and nine trace metals in mussel tissue. Mussels were collected in a naturally polluted area. Before the reference material was bottled, the mussel tissue was stabilised by freeze-drying, ground and sieved. For the material characterisation, several statistical tests were applied to check the homogeneity of the analytes in the tissue, and a stability test was performed to study the effect of the storage temperature in the analyte concentration. Other characteristics such as specific density, moisture and lipid contents as well as particle size distribution of the material were determined. Although the LRM had a homogeneous distribution for all PAHs and almost all metals, the stability study showed different results at both storage temperatures studied. For both PAHs and trace metals, the material was suitable to assure the quality control of the analysis.

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Research paper thumbnail of Permeation of Mixtures of Four Phenols through a Supported Liquid Membrane in NaCl 1.0 mol·dm Medium

Separation Science and Technology, 1999

Page 1. Permeation of Mixtures of Four Phenols through a Supported Liquid Membrane in NaCl 1.0 mo... more Page 1. Permeation of Mixtures of Four Phenols through a Supported Liquid Membrane in NaCl 1.0 mol搞m 3 Medium GORKA ARANA, GREGORIO BORGE, N仉TOR ETXEBARRIA, and LUIS ANGEL FERN篾DEZ* KIMIKA ANALITIKOAREN ...

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Research paper thumbnail of Determination of ion exchange equilibrium constants of strongly acidic resins with alkaline-earth metals by means of the potentiometric titrations technique

Talanta, 1999

A recently developed methodology for the determination of ion exchange equilibrium constants has ... more A recently developed methodology for the determination of ion exchange equilibrium constants has been applied to ion exchange systems of 1:2 stoichiometry. Potentiometric titrations with variable ionic strength were carried out. Ionic medium titrations were performed for the estimation of the liquid junction potential. The modified Bromley's methodology and the Wilson model were used for the estimation of the activity coefficients of the species in the aqueous and resin phase, respectively. A modification of the Henderson equation is used for the estimation of liquid junction potentials in the mixtures including 1:2 electrolytes. Equilibrium constants for the H+/M2+ (M=Mg, Ca, Sr and Ba) exchange systems in the strongly acidic resins Dowex CM-15 and Dowex C650 were studied.

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Research paper thumbnail of Potentiometric determination of the protonation constants of some phenols in 1.0 mol/L NaCl at 25°C

Fresenius Journal of Analytical Chemistry, 1994

The potentiometric determination of the protonation constants of phenol, 2-chlorophenol, 2-nitrop... more The potentiometric determination of the protonation constants of phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol and 2-methylphenol in 1.0 mol/L NaCl at 25°C is presented. An automated system has been used in the experiments. The determination of the constants has been carried out using both graphical and numerical methods.

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Research paper thumbnail of Potentiometric study of the distribution equilibria of phenols between 1.0 moldm −3 NaCl and organic solvents at 25 °C

Mikrochimica Acta, 1994

The potentiometric determination of the distribution coefficient of phenol, 2-chlorophenol, 2-nit... more The potentiometric determination of the distribution coefficient of phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol and 2-methyl-phenol between 1.0 mol dm−3 NaCl and five different organic solvents at 25 °C is presented. An automated potentiometric system was used and the determination of the constants was carried out using both graphical and numerical methods. The relevance of this study for the development of supported liquid membrane (SLM) recovery systems is discussed.

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Research paper thumbnail of Bronze analysis by k 0 NAA and PIXE

Journal of Radioanalytical and Nuclear Chemistry, 2003

Five copper alloys were prepared with modern powder metallurgical processes in the frame of the E... more Five copper alloys were prepared with modern powder metallurgical processes in the frame of the European project ‘Improvement of Means of Measurement on Archaeological Copper-Alloys for Characterisation and Conservation (IMMACO)’ and certified for As, Pb, Sn and Zn mass fractions. Similar in their composition to archaeological bronze alloys, these Certified Reference Materials (CRMs) are to be used for calibration of XRF instruments for characterization of archaeological samples either in the laboratory or in the field. This paper presents and compares the successful contribution of our non-destructive analytical methods (k 0-NAA and PIXE) to the IMMACO project and to the certification of the five reference materials.

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Research paper thumbnail of On-Line Multicomponent Determination of the Flux of Mixtures of Phenols Through a Liquid Membrane in Real Time

Mikrochimica Acta, 2001

The analysis of mixtures of four phenolic compounds in an on-line system using UV-visible measur... more The analysis of mixtures of four phenolic compounds in an on-line system using UV-visible measurements with a fibre optic probe is discussed in this work. The aim of this system is to provide accurate real time concentration profiles in order to monitor the transport of phenols across a solid supported liquid membrane in both the feed and stripping phases. Different calibration models are taking into account the pH of the solution, using experimental designs and the first derivative in combination with different multivariate approaches like multiple linear regression (MLR), inverted least squares (ILS) and partial least squares regression (PLS). The comparison of all these combinations is carried out by means of the predictive residual error sum of squares (PRESS) evaluated from an independent set of spectra. From this comparison it is concluded that a PLS model using first derivative spectra offers the most accurate and robust prediction in the permeation experiments. Additionally, the stability of the model and the figures of merit obtained are also discussed.

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Research paper thumbnail of Potentiometric study of the protonation and distribution equilibria of 2-chlorophenol in NaCl medium at 25 °C. Construction of a thermodynamic model

Talanta, 1996

The potentiometric determination of the protonation constant of 2-chlorophenol in NaCl media at d... more The potentiometric determination of the protonation constant of 2-chlorophenol in NaCl media at different ionic strengths and its distribution coefficient between these media and two organic solvents at 25 °C are presented. An automated potentiometric system was used, and the determination of the constants was carried out using both graphical and numerical methods. A thermodynamic model using the modified Bromley methodology has been constructed for the prediction of protonation constants and distribution coefficients in NaCl media. The relevance of this study to the development of supported liquid membrane recovery systems is discussed.

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Research paper thumbnail of Is It Safe to Use Poisson Statistics in Nuclear Spectrometry?

Journal of Radioanalytical and Nuclear Chemistry, 2000

The boundary conditions in which Poisson statistics can be applied in nuclear spectrometry are in... more The boundary conditions in which Poisson statistics can be applied in nuclear spectrometry are investigated. Improved formulas for the uncertainty of nuclear counting with deadtime and pulse pileup are presented. A comparison is made between the expected statistical uncertainty for loss-free counting, fixed live-time and fixed real-time measurements.

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Research paper thumbnail of Classification of archaeological pieces into their respective stratum by a chemometric model based on the soil concentration of 25 selected elements

Spectrochimica Acta Part B-atomic Spectroscopy, 2010

The aim of this work was to demonstrate that an archaeological ceramic piece has remained buried ... more The aim of this work was to demonstrate that an archaeological ceramic piece has remained buried underground in the same stratum for centuries without being removed. For this purpose, a chemometric model based on Principal Component Analysis, Soft Independent Modelling of Class Analogy and Linear Discriminant Analysis classification techniques was created with the concentration of some selected elements of both soil of the stratum and soil adhered to the ceramic piece. Some ceramic pieces from four different stratigraphic units, coming from a roman archaeological site in Alava (North of Spain), and its respective stratum soils were collected. The soil adhered to the ceramic pieces was removed and treated in the same way as the soil from its respective stratum. The digestion was carried out following the US Environmental Pollution Agency EPA 3051A method. A total of 54 elements were determined in the extracts by a rapid screening inductively coupled plasma mass spectrometry method. After rejecting the major elements and those which could have changed from the original composition of the soils (migration or retention from/to the buried objects), the following elements (25) were finally taken into account to construct the model: Li, V, Co, As, Y, Nb, Sn, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Au, Th and U. A total of 33 subsamples were treated from 10 soils belonging to 4 different stratigraphic units. The final model groups and discriminate them in four groups, according to the stratigraphic unit, having both the stratum and soils adhered to the pieces falling down in the same group.

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Research paper thumbnail of Calcium inhibits diacylglycerol uptake by serum albumin

Biochimica Et Biophysica Acta-biomembranes, 2009

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Research paper thumbnail of Pattern recognition and classification of sediments according to their metal content using chemometric tools. A case study: The estuary of Nerbioi-Ibaizabal River (Bilbao, Basque Country)

Chemosphere, 2011

Chemometrics are increasingly used in environmental monitoring studies, but are still far from be... more Chemometrics are increasingly used in environmental monitoring studies, but are still far from being accepted as routine tools by field specialists. The multivariate character of usually highly correlated environmental data recommends the use of advanced chemometrics as part of the analytical methodology in order to get information on the basic structure of data. In this work, we have applied a battery of non-supervised (Principal Component Analysis (PCA)) and supervised (k-Nearest Neighbour (k-NN), Soft Independent Modelling of Class Analogies (SIMCA), Linear Discriminant Analysis (LDA) and Artificial Neural Networks (ANNs)) multivariate techniques on a specific environmental dataset. The dataset consists on the concentration of 14 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn) in 95 sediments collected at eight different locations of the estuary of the Nerbioi-Ibaizabal River (Bilbao, Basque Country) during 12 sampling campaigns conducted every 3 months between 2005 and 2008. The study aims to present a simple methodology of general applicability which may result in a flexible and practical tool to assess chemical pollution in sediments of a given specific site.► Long-term monitoring of pollution in the estuary of the Nerbioi-Ibaizabal River. ► Sediments as indicators of metal pollution in estuaries. ► Combination of chemometric techniques for pattern recognition and classification. ► Chemometric classification of sediments according to their metal content.

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Research paper thumbnail of Multisimplex Optimisation of the Purge-and-Trap Preconcentration of Volatile Fatty Acids, Phenols and Indoles in Cow Slurries

Chromatographia, 2008

In this work the simultaneous purge-and-trap (P&T) preconcentration of volatile fatty acids (acet... more In this work the simultaneous purge-and-trap (P&T) preconcentration of volatile fatty acids (acetic acid, propanoic acid, butanoic acid, iso-butanoic acid, pentanoic acid, iso-pentanoic acid, hexanoic acid and heptanoic acid), phenols (phenol, 4-methylphenol and 4-ethylphenol) and indoles (indole and 3-methylindole) from cow slurries was carried out in order to quantify them by gas chromatography flame ionisation detection (GC–FID). The optimisation of the preconcentration was performed using spiked cow slurries and the variables studied were the nature of the trap, the purge and heating time and the amount of inert salt (NaCl) added. Other parameters such as purge flow, sample volume, desorption time and temperature and baking time and temperature were kept constant. The first variable studied was the nature of the preconcentration trap. Four different commercially available traps (Vocarb 4000, Vocarb 3000, BTEXTRAP and Tenax/silica gel/carbon) were studied and Vocarb 3000 gave best results. Once the optimum trap was chosen, appearance of possible memory peaks were studied and significant signals were observed for 4-methylphenol, 4-ethylphenol, indole and 3-methylindole. In order to improve the blanks after each analysis the following actions were taken: (1) the needle sparger was located in the headspace of the sample and (2) all the replaceable parts of the P&T (sample tube, needle sparger, Teflon ferrules, nuts, etc.) were washed, sonicated in acetone for 15 min and dried in an oven at 350 °C. Once the blank problems were minimised, the remaining variables (purge and heating time and the amount of NaCl) were optimised using the MultiSimplex® program, which enabled the study of several variables and responses simultaneously. Optimum conditions for the simultaneous preconcentration were obtained after 24 experiments and the final optimised preconcentration conditions were as follows: 0.4 g of NaCl were added to 10 mL sample which was heated at 80 °C for 10 min and purged for 20 min while the Vocarb 3000 trap remained at room temperature. Once the purge step was over, the trap was desorbed at 250 °C for 6 min and baked at 260 °C for 10 min. After the optimisation of the P&T based preconcentration, the precision (within and among days), accuracy and detection limits of the method were studied.

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Research paper thumbnail of Spectroscopic evaluation of the environmental impact on black crusted modern mortars in urban–industrial areas

Analytical and Bioanalytical Chemistry, 2011

A multianalytical characterisation of black crusted modern construction materials from buildings ... more A multianalytical characterisation of black crusted modern construction materials from buildings located in the Bilbao Metropolitan area (North Spain) was carried out. According to the mineral composition determined by Raman spectroscopy, calcite and hematite were the major compounds found while aragonite, limonite, rutile, quartz and some aluminosilicates such as obsidian or amazonite (KAlSi3O8) were also present in minor percentages. As deterioration products, gypsum and anhydrite were widely found not only in the surface but also in the inner part of strongly deteriorated samples. Coquimbite (Fe2(SO4)3·9H2O) was identified as well in the most protected facade where high amounts of Fe, having probably an anthropogenic origin, were measured by micro X-ray fluorescence (μ-XRF). Zn was found to be in high amounts while Cu, Pb, Ti, Mn, Sr and K were identified as minor elements. Considering the non-expected concentrations found for some anthropogenic elements, a sequential extraction was carried out in order to determine their chemical form by means of ion chromatography and inductively coupled plasma mass spectrometry. The orientation of the facades, which had a different influence from rain washing and industrial and traffic impact, was shown to affect the accumulation of different compounds in the black crust. Finally, the MEDUSA software was used to simulate the reactions among the original compounds, deposited pollutants and the atmospheric acid gases in order to explain the presence of the decaying species found. Figure Multianalytical Speciation protocol applied on the analysis of modern mortars

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Research paper thumbnail of Selenium in electrolytic manganese as a reference material for the quality control of aluminium melts

Accreditation and Quality Assurance, 2007

Electrolytic manganese is an important alloying element for aluminium and steel melts. It is main... more Electrolytic manganese is an important alloying element for aluminium and steel melts. It is mainly added to melts of aluminium in the holding furnace as tablets or minitablets (compressed compacts of manganese and aluminium powders). Selenium derivates are usually added during the production of electrolytic manganese, so some selenium is present in the alloys produced when electrolytic manganese is added to the aluminium furnace. Since the selenium contents of many alloys are of concern from health and environmental perspectives, their values should be provided. In this work, a laboratory reference material (LRM) based on electrolytic manganese was produced to assure our routine quality control method, where selenium is analysed by hydride generation followed by optical emission spectrometry with inductively coupled plasma (HG–ICP–OES). Therefore, the present paper describes in detail the preparation procedure for and the results from homogeneity and stability studies performed on electrolytic manganese LRM. For this purpose, a commercial electrolytic manganese lot was selected and the main factors involved in the preparation of the material (pretreatment step, homogenization, bottling and storage) were carefully studied and established in order to guarantee the long-term stability of the LRM. The results obtained showed that the LRM developed was a fit-for-purpose material for the quality control of the routine analysis of selenium.

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Research paper thumbnail of Diagnosing the Impact of Traffic on Roadside Soils Through Chemometric Analysis on the Concentrations of More Than 60 Metals Measured by ICP/MS

This study aims to establish the impact of traffic pollution at two parallel roads in the provinc... more This study aims to establish the impact of traffic pollution at two parallel roads in the province of Biscay (North of Spain). Soil samples digestions were carried out following the EPA 3051A method and the extracts were analyzed by ICP/MS. A rapid screening method for the determination of more than 60 metals is proposed. The subsequent chemometric treatment of the obtained data shows the presence of more than ten traffic related metals: Cd, Cr, Cu, Hf, Mo, Nb, Ni, Pb, Sb, Sn, Sr, Zn and Zr. Different soil types (in the old road and in the highway) can be distinguished by means of its rare earth and alkaline metal concentration. Very high concentrations of Zn were found in soil under the guard rail.

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Research paper thumbnail of The effect of the nature of the polymer backbone on the stability and the analytical response of polymer-modified electrodes

Electroanalysis, 1995

The synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)2(PS)... more The synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)2(PS)7.5(DMAP)2.5Cl]Cl, where bipy = 2,2′-bipyridyl, PS = polystyrene, and DMAP = poly[4-(N-methyl-N-p-vinylbenzylamino) pyridine], are described. The charge transport properties of electrodes modified with the redox material are investigated using cyclic voltammetry and chronoamperometry. The modified electrode behaves as an efficient electrocatalyst for the outer-sphere reduction of FeIII, with the cross-exchange reaction occurring at the surface of the polymer (Sk″) at concentrations less than 1.0 × 10−3 mol dm−3 FeIII, with a change over to the Ste, kinetic regime at higher substrate concentrations. Direct agreement was observed between the kinetic behavior at rotating disk electrodes and in thin-layer flow cells. Application of the modified electrodes for the determination of iron in pharmaceutical formulations and the long term stability of the electrodes are investigated. The results obtained are compared with those reported for the analogous metallopolymer [Os(bipy)2(PVP)10Cl]Cl, where PVP is poly-4-vinylpyridine.

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Research paper thumbnail of Hydrolysis of Nb(V) and Ta(V) in aqueous KCl at 25°C. Part II: Construction of a thermodynamic model for Ta(V)

Journal of Solution Chemistry, 1995

In this work the hydrolysis of Ta(V) in 3.0M KCl has been studied by measuring the H3O+ ion conce... more In this work the hydrolysis of Ta(V) in 3.0M KCl has been studied by measuring the H3O+ ion concentration with a glass electrode. The experimental work consisted of automatically controlled potentiometric titrations. The results were treated using graphical and numerical methods and, as a result, the hydrolysis process can be considered as a homonuclear protolysis. Finally, the results obtained were compared with other data found in the literature and a hydrolysis model for Ta(V) was built by means of the modified Bromley theory.

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Research paper thumbnail of Headspace-solid-phase microextraction preconcentration of phenols, indoles and on-fibre derivatised volatile fatty acids in liquid and gas samples from cow slurries

Journal of Separation Science, 2007

Odorous organic compounds from liquid and gas samples of animal wastes were studied by headspace ... more Odorous organic compounds from liquid and gas samples of animal wastes were studied by headspace (HS)-solid-phase microextraction (SPME)-GC-MS. 1-Pirenyldiazomethane (PDAM) was adsorbed/absorbed on the SPME fibre in order to obtain the corresponding ester derivatives during the preconcentration step. The SPME fibre was immersed into a PDAM solution. Then, the SPME fibre was withdrawn and exposed to the HS of the liquid cow slurry. This way derivatisation of VFAs took place in the SPME fibre together with the preconcentration of the rest of the analytes of interest. The analytes were desorbed in the hot injection port (300°C) of a GC-MS for 3 min. Four different fibre types and different immersion periods of the fibre in the PDAM solution were studied in order to obtain the best sensitivity with the selected fibre. Accuracy, precision and the LODs were calculated using spiked liquid and gas samples. The possibility of storing liquid samples after sampling by preconcentration on the fibre was also considered. Storage time and temperature were studied. The optimised method was applied to the determination of the analytes in liquid and gas samples from cow slurries from an intensive production farm.

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Research paper thumbnail of Risk assessment of trace elements in sediments: The case of the estuary of the Nerbioi–Ibaizabal River (Basque Country)

Journal of Hazardous Materials, 2010

Long term (January 2005–January 2008) monitoring of sediments was used to investigate metal pollu... more Long term (January 2005–January 2008) monitoring of sediments was used to investigate metal pollution in the estuary of the Nerbioi–Ibaizabal River (Bilbao, Basque Country). Sediments were collected from eight representative locations of the estuary approximately every three months. The concentration of fourteen elements was measured in sediment extracts. Different graphical representations of the data set, simple statistical methods and sediment quality guidelines were combined to investigate trends in space and time, identify pollution sources, and assess sediment quality from a toxicological point of view. In general terms, the main trend reveals a significant fall in metal concentration over the period investigated. There are still certain points of the estuary with relatively high concentration of toxic metals, but the toxicological approach suggests that the risk for living organisms is not important.

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Research paper thumbnail of Preparation of a reference mussel tissue material for polycyclic aromatic hydrocarbons and trace metals determination

Analytica Chimica Acta, 2010

Due to high cost of certified reference materials (CRMs), reference materials (RMs) are preferred... more Due to high cost of certified reference materials (CRMs), reference materials (RMs) are preferred to check the method performance in environmental analysis. In this work, a laboratory reference material (LRM) was prepared and characterised to carry out the quality control in monitoring analysis of eight polycyclic aromatic hydrocarbons (PAHs) and nine trace metals in mussel tissue. Mussels were collected in a naturally polluted area. Before the reference material was bottled, the mussel tissue was stabilised by freeze-drying, ground and sieved. For the material characterisation, several statistical tests were applied to check the homogeneity of the analytes in the tissue, and a stability test was performed to study the effect of the storage temperature in the analyte concentration. Other characteristics such as specific density, moisture and lipid contents as well as particle size distribution of the material were determined. Although the LRM had a homogeneous distribution for all PAHs and almost all metals, the stability study showed different results at both storage temperatures studied. For both PAHs and trace metals, the material was suitable to assure the quality control of the analysis.

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Research paper thumbnail of Permeation of Mixtures of Four Phenols through a Supported Liquid Membrane in NaCl 1.0 mol·dm Medium

Separation Science and Technology, 1999

Page 1. Permeation of Mixtures of Four Phenols through a Supported Liquid Membrane in NaCl 1.0 mo... more Page 1. Permeation of Mixtures of Four Phenols through a Supported Liquid Membrane in NaCl 1.0 mol搞m 3 Medium GORKA ARANA, GREGORIO BORGE, N仉TOR ETXEBARRIA, and LUIS ANGEL FERN篾DEZ* KIMIKA ANALITIKOAREN ...

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Research paper thumbnail of Determination of ion exchange equilibrium constants of strongly acidic resins with alkaline-earth metals by means of the potentiometric titrations technique

Talanta, 1999

A recently developed methodology for the determination of ion exchange equilibrium constants has ... more A recently developed methodology for the determination of ion exchange equilibrium constants has been applied to ion exchange systems of 1:2 stoichiometry. Potentiometric titrations with variable ionic strength were carried out. Ionic medium titrations were performed for the estimation of the liquid junction potential. The modified Bromley's methodology and the Wilson model were used for the estimation of the activity coefficients of the species in the aqueous and resin phase, respectively. A modification of the Henderson equation is used for the estimation of liquid junction potentials in the mixtures including 1:2 electrolytes. Equilibrium constants for the H+/M2+ (M=Mg, Ca, Sr and Ba) exchange systems in the strongly acidic resins Dowex CM-15 and Dowex C650 were studied.

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