Rafael Beltrán

Evaluation of atomic fluorescence spectrometry as a sensitive detection technique for arsenic speciation

The potential of coupling anion-exchange high-performance liquid chromatography, hydride generation and atomic fluorescence spectrometry (HPLC–HG–AFS) for arsenic speciation is considered. The effects of hydrochloric acid and sodium tetrahydroborate concentrations on signal-to-background ratio, as well as argon and hydrogen flow rates, were investigated. Detection limits for arsenite, dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate were 0.17, 0.45, 0.30 and 0.38 μg l−1, respectively, using a 20-μl loop. Linearity ranges were 0.1–500 ng for As(III) and MMA (as arsenic), and 0.1–800 ng for DMA and As(V) (as arsenic). Arsenobetaine (AsB) was also determined by introducing an on-line photo-oxidation step after the chromatographic separation. In this case the limits of detection and linear ranges for the different species studied were similar to the values obtained previously for As(V). The technique was tested with a human urine reference material and a volunteers sample.

Precipitation, pH and metal load in AMD river basins: an application of fuzzy clustering algorithms to the process characterization

In the present work, Acid Mine Drainage (AMD) processes in the Chorrito Stream, which flows into the Cobica River (Iberian Pyrite Belt, Southwest Spain) are characterized by means of clustering techniques based on fuzzy logic. Also, pH behavior in contrast to precipitation is clearly explained, proving that the influence of rainfall inputs on the acidity and, as a result, on the metal load of a riverbed undergoing AMD processes highly depends on the moment when it occurs. In general, the riverbed dynamic behavior is the response to the sum of instant stimuli produced by isolated rainfall, the seasonal memory depending on the moment of the target hydrological year and, finally, the own inertia of the river basin, as a result of an accumulation process caused by age-long mining activity.

Comparison of Different Extraction Methods to Determine Phenolic Compounds in Virgin Olive Oil

A comparison between different extraction methods has been performed in order to assess their effectiveness for the analysis of total phenols (liquid–liquid extraction (LLE), liquid–liquid micro extraction (LLME), and ultrasound liquid–liquid extraction (USE)) and individual phenols (LLME, USE, and solid-phase extraction (SPE)) from virgin olive oil (VOO). Statistical analysis of the analytical data obtained for the total phenol content of a VOO, showed that LLME and USE can represent a reliable alternative to the traditional procedure based on LLE that needs more amount of sample, generates more wastes, and is more time consuming. When an olive oil spiked with phenols was used to test the efficiency of LLME, USE, and SPE methods, the statistical analysis of the data obtained for each individual phenol, again proved LLME and USE methods to be the most suitable, in terms of precision and recoveries, for this purpose. The analysis of real samples (Arbequina and Picual cultivars) confirmed the results obtained for the spiked oil.

Optimization of an HPLC-HG-AFS method for screening Sb(V), Sb(III), and Me3SbBr2 in water samples

A procedure for the separation and determination of inorganic and organic species of antimony based on the use of coupled high-performance liquid chromatography (HPLC) hydride generation (HG) atomic fluorescence spectrometry (AFS) is described. Me3SbBr2 and inorganic Sb(V) and Sb(III) were separated on an anion-exchange column [Hamilton PRPX-100 (100 × 4.1 mm)] using the concentration gradient between potassium hydroxide, 20 mM pH 11, and ammonium tartrate, 200 mM pH 5. The flow rate through the column was 1.5 mL min−1. The retention times were 0.98, 1.71 and 5.03 min for Me3SbBr2, Sb(V) and Sb(III), respectively. The hydrides were generated on-line with 3% m/v NaBH4 and 2 mol l−1 HNO3 solutions. The intensity of emission was linearly related to the concentration of the derivatized Me3SbBr2 species in the range 1.0–50.0 µg l−1 (r = 0.9996), Sb(V) species in the range 1.0–50.0 µg l−1 (r = 0.9998) and Sb(III) in the range 2.5–50.0 µg l−1 (r = 0.9998), with detection limits of 0.04 µg l−1 for Me3SbBr2, 0.09 µg l−1 for Sb(V) and 0.26 µg l−1 for Sb(III). The precisions evaluated using the relative standard deviation (RSD) were 6.8%, 2.4% and 3.3% for Me3SbBr2, Sb(V) and Sb(III), respectively. The method has a sensitivity suitable for monitoring drinking and surface waters according to the regulations established by the EU directives for antimony (10 ug 1−1), and it was applied to the speciation of inorganic and organic antimony in several spiked water samples. The precisions for well water, Merck and mineral water were limited in relation to Me3SbBr2 due to its conversion to Sb(V).

Arsenic Speciation in Biological Samples Using the Couplings HPLC-UV-HG-AAS and HPLC-UV-HG-AFS

Abstract A speciation procedure for arsenobetaine (AsB), arsenite (AsIII), dimethylarsinic acid (DMA), mono-methylarsonic acid (MMA) and arsenate (Asv) based on the couplings HPLC-HG-AFS and HPLC-UV-HG-AFS has been developed and results compared with HPLC-HG-AAS and HPLC-UV-HG-AAS. AFS detection improves the performance of these couplings, being the detection limits about twenty times lower (from 0.06 to 0.14 μg l−1 for AFS against 1.1 to 3.9 μg l−1 for AAS). The linear range extends from 0.25 to 8000 μg l−1 for AFS in contrast to 5 to 500 μg l−1 for AAS. This approach has been applied to the arsenic speciation in biological tissues (certified material TORT-1 and fresh bivalve tissues) in which arsenobetaine was the main species found. Extraction of the species has been carried out using repetitive extractions with methanol and methanol/water (1:1) mixtures being the later more suitable for quantitative recovery.

Extraction and Determination of Phenolic Compounds in the Berries of Sorbus americana Marsh and Lonicera oblongifolia (Goldie) Hook

Phenolic compound content in Sorbus americana Marsh and Lonicera oblongifolia (Goldie) Hook berries was determined for the first time. An improved solid-liquid microextraction (SLME) method combining with high-performance liquid chromatography (HPLC)-diode array detector (DAD)-mass spectrometry (MS) has been developed to determine the phenolic compounds present in these berries, reducing the amount of sample, reagents, and time consumed. The major phenolic compound identified and quantified was 3-O-caffeoylquinic acid (3-CQA) in both berries. To a lesser extent, 5-O-caffeoylquinic acid (5-CQA) and quercetin-3-O-glucoside (QG) were also determined. The existence of these phenolic compounds and the great abundance of these fruits in the northeast of North America make S. americana Marsh and L. oblongifolia Hook berries a new and excellent source of natural phenolic compounds (antioxidants), which can be very useful in biotechnological exploitation.

Acid Leaching/Solvent Extraction Treatment of Sediment Samples for Organotin Speciation

A method is described for leaching of nanogram amounts of monobutylin (MBT), dibutyltin (DBT) and tributyltin (TBT) and monophenyltin (MPT), diphenyltin (DPT) and triphenyltin (TPT) from sediments. The procedure is based on soaking the sediments in water-hydrogen bromide mixture (1:1) with magnetic stirring for 30 min followed by extraction with 0.04% (w/v) tropolone solution in dichloromethane for 2 h. Organotins are determined by gas chromatography with a flame photometric detector (GC-FPD) after cleanup through a Florisil column and derivatization by Grignard pentylation. The method has been applied to the study of water and sediments in different areas of the south-west Spain. Predominant species are butyltins, especially TBT which rise critical levels in waters and sediments of fishering harbours. In this study it has been found a direct relation between organotin levels and distance to potential sources determined by boating activities. In addition, it has been verified the relative occurrence of DBT and MBT together with TBT, possibly as a result of a degradation process, and the influence of sediment grain size and organic matter content on organotins accumulation.

Combination of complementary data mining methods for geographical characterization of extra virgin olive oils based on mineral composition

This work explores the potential of multi-element fingerprinting in combination with advanced data mining strategies to assess the geographical origin of extra virgin olive oil samples. For this purpose, the concentrations of 55 elements were determined in 125 oil samples from multiple Spanish geographic areas. Several unsupervised and supervised multivariate statistical techniques were used to build classification models and investigate the relationship between mineral composition of olive oils and their provenance. Results showed that Spanish extra virgin olive oils exhibit characteristic element profiles, which can be differentiated on the basis of their origin in accordance with three geographical areas: Atlantic coast (Huelva province), Mediterranean coast and inland regions. Furthermore, statistical modelling yielded high sensitivity and specificity, principally when random forest and support vector machines were employed, thus demonstrating the utility of these techniques in food traceability and authenticity research.

Characterization and evaluation of phenolic profiles and color as potential discriminating features among Spanish extra virgin olive oils with protected designation of origin

Changes in phenolic profiles and color parameters can help to differentiate between extra virgin olive oils (EVOOs) with protected designation of origin (PDO). Phenolic profile characterization and CIELAB parameters determination of 9 PDO EVOOs from Spain were developed. Both properties of EVOOs are very relevant to their commercialization and increase the product value. The Serrana de Espadán olive cultivar was characterized for the first time and showed the highest pinoresinol concentrations and clarities in these olive oils, which are important values for the product image. To detect fraudulent instrumental work and implement quality control, principal component analysis (PCA) and linear discriminant analysis (LDA) were performed. EVOO geographical origin and cultivar distributions were achieved with cumulative variances of 93.4% and 92.4%, respectively. A categorization of PDO EVOOs was proposed using the following 7 phenolic compounds: phenolic alcohols (tyrosol and hydroxytyrosol), 3,4-DHPEA-EDA, 3,4-DHPEA-EA, p-HPEA-EDA, pinoresinol and total phenolic compounds.

Desarrollo de Procedimientos Normalizados de Trabajo: una forma Innovadora de realizar las Prácticas en Asignaturas de Ciencias Experimentales

The present work proposes the use of autonomous learning for students through the elaboration of standard operating procedures (SOPs). This experience is carried out within the course Analytical Methods for Quality Assurance of the majors Chemical Engineering and Technical Industrial Engineering in Chemistry at the University of Huelva in Spain. The preparation of the SOPs and the working instructions make that repetitive actions are performed in the same way regardless of the person who performs the tasks. Therefore, SOPs represent a good tool in the practical formation of students. The degree of satisfaction of the students in using this method of autonomous learning has been evaluated through individual interviews, group tutorial and opinion polls. The results have been satisfactory and the activity has resulted to be a motivating agent for the learning process.En este trabajo se plantea al alumno el aprendizaje autonomo mediante la elaboracion de procedimientos normalizados de trabajo (PNTs). La experiencia se realiza en la asignatura Metodos Analiticos de Control de Calidad del plan de Ingenieria Quimica y de Ingenieria Tecnica Industrial especialidad Quimica de la Universidad de Huelva en Espana. La elaboracion de los PNTs e instrucciones de trabajo facilitan que las tareas repetitivas se realicen siempre de la misma forma con independencia de la persona que las realiza, constituyendo una buena herramienta para la formacion practica del alumnado. El grado de satisfaccion del alumno para el aprendizaje autonomo ha sido evaluado a traves de entrevistas personales, tutorias grupales y encuestas. Los resultados han sido muy satisfactorios y la actividad ha resultado ser un importante agente motivador del aprendizajeThe present work proposes the use of autonomous learning for students through the elaboration of standard operating procedures (SOPs). This experience is carried out within the course Analytical Methods for Quality Assurance of the majors Chemical Engineering and Technical Industrial Engineering in Chemistry at the University of Huelva in Spain. The preparation of the SOPs and the working instructions make that repetitive actions are performed in the same way regardless of the person who performs the tasks. Therefore, SOPs represent a good tool in the practical formation of students. The degree of satisfaction of the students in using this method of autonomous learning has been evaluated through individual interviews, group tutorial and opinion polls. The results have been satisfactory and the activity has resulted to be a motivating agent for the learning process.