José A. López-López

Simple hollow fiber liquid membrane based pre-concentration of silver for atomic absorption spectrometry

Silver pollution has gained attention in the last few years because silver is being massively used as a bactericide in self-care, medical and textile products. Difficulties of Ag determination are associated with the very low concentrations in which it is normally found (ng L−1) and the nature of the sample matrix. Standard methods such as liquid–liquid extraction (LLE) are regularly used. Alternatively, liquid phase micro-extraction (LPME) appears to be an environmentally friendly tool for sample treatment that offers higher pre-concentration factors. This allows the determination of ultra-trace levels of silver using standard instrumental techniques such as atomic absorption spectrometry. In this work, a hollow fiber LPME is proposed. Silver pre-concentration has been conducted using tri-isobutylphosphine sulphide (TIBPS) as a carrier from the sample to an acceptor solution through a solvent placed in the fiber pores. Accurel-PP 50/280 fibers with an internal volume of 20 μL were used for 50 mL samples. After optimization, 0.1 M KNO3 in the sample, 0.1 M TIBPS in dihexyl ether as the organic phase and 1 M Na2S2O3 in the acceptor solution were established. The system offers enrichment factors of 1053 times, a limit of detection of 1.16 ng L−1. This method improves the limit of detection of the most recent liquid micro-extraction methods for silver pre-concentration coupled with GFAAS, being in this case comparable to ICP-MS detection based techniques.

A chemometric approach to the evaluation of atmospheric and fluvial pollutant inputs in aquatic systems: the Guadalquivir River estuary as a case study.

To establish the quality of waters it is necessary to identify both point and non-point pollution sources. In this work, we propose the combination of clean analytical methodologies and chemometric tools to study discrete and diffuse pollution caused in a river by tributaries and precipitations, respectively. During a two-year period, water samples were taken in the Guadalquivir river (selected as a case study) and its main tributaries before and after precipitations. Samples were characterized by analysing nutrients, pH, dissolved oxygen, total and volatile suspended solids, carbon species, and heavy metals. Results were used to estimate fluvial and atmospheric inputs and as tracers for anthropic activities. Multivariate analysis was used to estimate the background pollution, and to identify pollution inputs. Principal Component Analysis and Cluster Analysis were used as data exploratory tools, while box-whiskers plots and Linear Discriminant Analysis were used to analyse and distinguish the different types of water samples.

A new analytical method for selective pre-concentration of free silver in estuarine waters using liquid membranes.

Silver is recognized as an important pollutant of natural waters. This element is a selective tracer of anthropogenic pollution related to sewage. Studying its bio-availability requires the application of specific separation of the free ion. A liquid membrane is proposed for separating Ag(+) from estuarine water samples. A bulk liquid membrane (BLM) has been selected. Free silver is transported from the sample to a receiving solution through an organic membrane containing tri-isobutylphosphine sulfide (TIBPS). Effects of formation of chlorinated and organic complexes on silver pertraction have been evaluated. The extent of formation of the aforementioned complexes has been based on the decrease of silver transport to the receiving phase, measured as enrichment factor (EF), because only Ag(+) is assumed to be transported. Finally, after quantifying the effects of the employed ligands on EF, total concentration of silver can be estimated from the experimental data of Ag(+) analyzed by the proposed BLM system.

Solvent bar micro-extraction: Improving hollow fiber liquid phase micro-extraction applicability in the determination of Ni in seawater samples

During the last decade, hollow fiber liquid phase micro-extraction (HF-LPME) has become an attractive alternative in sample treatment for the analysis of trace metals in seawater. If compared with other similar methodologies, its main advantages are associated to a higher stability of the organic solution contained into the pores of the fiber, which acts as a lipophilic membrane during the extraction process. However there are some remaining problems that makes its use difficult, mostly related to the need of increasing the rate of analysis and improving portability. In this paper a novel three phase solvent bar micro-extraction (3PSBME) for the fiber device has been proposed. Its main advantage is that the 3PSBME device can be left free in the sample. This way the system is portable, and no special support is needed leading to the possibility of simultaneous extraction of several samples. In this work, multivariate central composite design of experiment has been carried out to optimize Ni pre-concentration using di-2-ethylhexyl phosphoric acid (DEHPA) as extractant and HNO3 as acceptor agent. Factors influencing extraction have been the pH in the sample and the fiber length. For seawater samples, Ni can be pre-concentrated 11 times in 140 min. The method presents RSD 9.42% and limit of detection 44 ng L(-1), using GFAAS for instrumental determination. It has been applied for determination of Ni in seawater, including a reference material CRM-403 proving its applicability.

Solvent bar micro-extraction (SBME) based determination of PAHs in seawater samples

Measuring the impact of PAHs in seawater samples is often difficult due to the low concentrations in which they appear and the complexity of the sample matrix. Traditional methods for sample preparation such as liquid-liquid extraction and solid phase extraction require the use of excessive amounts of solvents and reagents, and sample handling. In this work, hollow fiber liquid phase micro-extraction (HFLPME), in the configuration of solvent bar micro-extraction (SBME), was proposed as an environmentally friendly and more effective tool, for the extraction of the 16 priority PAHs from seawater samples. Extraction was conducted using hexane as a solvent. Enrichment factors from 45 to 163 were obtained after 60min at a stirring rate of 500rpm in the sample. Moreover, a negative linear relationship was observed between the enrichment factor and the molecular weight of the PAHs. Under optimized conditions, the limits of detection were in the range from 0.21 to 0.82ngL-1, the method showed a linear response up to 500μgL-1, and the average relative standard deviation for seawater samples spiked with 5ngL-1 was 11.6%. After calibration, the SBME was applied to extract PAHs in seawater samples from the Bay of Cadiz (SW Spain), showing an average recovery of 99%. In conclusion, the SBME is an environmentally friendly, one-step alternative for sample preparation in the determination of PAHs in seawater samples.

Three-phase solvent bar micro-extraction as an approach to silver ultra-traces speciation in estuarine water samples

Silver ion inputs into the environment due to human activities have been increased in the last years because it has been used as a bactericide with application in medical, homecare and self-care products. In addition, it is toxic at low concentration for aquatic organisms. In estuarine waters, salinity and dissolved organic matter (DOM) regulate Ag(+) concentration by the formation of complexes as AgCln((n-1)-) and Ag-DOM. Difficulties of Ag(+) analysis in estuaries are associated to its low concentration level and interferences of sample matrix. Liquid and solid phase extraction methods have been used for speciation of silver in waters; however, miniaturized methods that offer a better environmental profile are desirable. Hollow fiber liquid phase micro-extraction (HFLPME) allows obtaining higher pre-concentration factors with a reduction of waste generation. Notwithstanding, some operational improvements are needed to permit their use as a routine method that can be afforded using a configuration of three-phase solvent bar micro-extraction (3PSBME). In this work, tri-isobutylphosphine sulphide (TIBPS) has been used as an extractant for Ag(+) pre-concentration in estuarine waters by 3PSBME. Under optimized conditions, Ag(+) has been pre-concentrated 60 times and the method presents a limit of detection of 1.53 ng L(-1). To evaluate which Ag species is transported by TIBPS, Cl(-) and DOM have been added to synthetic samples. As a result, a decrease in Ag pre-concentration efficiency after additions has been observed and quantified. Results showed that Ag(+) is selectively transported by TIBPS from estuarine water samples after comparison of the results with those obtained by the reference method of liquid extraction with APDC/DDDC.

Solvent bar micro-extraction with graphite atomic absorption spectrometry for the determination of silver in ocean water

Main drawbacks for silver determination in seawater are the effects of samples matrix and that Ag appears in the sub ng L(-1). Available methods for sample preparation in Ag analysis are based on solid and liquid extraction using tedious process that increase the cost of analysis and the risk of sample contamination, producing important waste amounts. Solvent bar micro-extraction (SBME) allows the pre-concentration of Ag in a micro-volume of the ionic liquid Aliquat 336® in kerosene solution. For this reason, it is considered as a green alternative to standard methods. The method has been optimized using synthetic seawater samples, offering the highest response for samples at pH=2, using 5% Aliquat 336® dissolved in kerosene containing 5% dodecan-1-ol as acceptor solution and after 1h stirring at 800rpm. The method exhibited linearity up to 50ngL(-1), with a limit of detection of 0.09ngL(-1), covering the concentration range of interest for environmental studies. Finally, it was applied for determination of Ag in real seawater samples, and the results were compared with the reference method of liquid-liquid extraction with 1-pyrrolidine-dithiocarbamate and diethylammonium-diethyldithiocarbamate, showing the applicability of ionic liquid based SBME using Aliquat 336(®) for the simple monitoring of silver ultra-traces in seawater analysis.

A new contamination-free method for the determination of traces of anthropogenic silver in freshwaters

The use of different products containing silver in anthropic activities has caused the increase of silver concentrations in many water courses. To establish their toxic effects, both precise and accurate analytical methods are needed to quantify silver at very low concentrations. Although different methods may be found in the literature, in practice, most chemists or other environmentalists use solvent extraction methodology in a Clean Lab, which is tedious and with high risk of sample contamination during manipulation. In this work, the applicability of a liquid membrane-based method was studied as an alternative for the analysis of silver in freshwaters using triisobutylphosphine sulphide, TIBPS (Cyanex 471X©), as a carrier. Transport conditions were studied and optimised; including pH and co-ion (nitrate) concentration in sample, the influence of anionic species present in freshwaters, and concentrations of carrier and stripping reagent. Under optimum conditions an extraction efficiency of 59.5% was achieved after a 4-hours operation time. Since both extraction and back-extraction processes are carried out simultaneously and without sample manipulation, this system offers a clean alternative (avoiding contamination) for determination of traces and ultra-traces of silver in freshwaters. The system was successfully applied to the preconcentration of silver, in tap and freshwater samples, before their quantification by flame atomic absorption spectroscopy (FAAS) at a ppb-level or by inductively coupled plasma-mass spectrometry (ICP-MS) at the ppt-level.

A simple and economical spectrofluorimetric alternative for Al routine analysis in seafood

A simple and economical spectrofluorimetric alternative for aluminium determination in bivalve mollusks based on the fluorescent blue-green colour complex between Al(III) and salicylaldehyde picolinoylhydrazone (SAPH) has been studied. The factors that are most likely to affect were optimized with a Box-Behnken design. Optimum conditions were: pH 6.6, 0.9 mol L-1 acetic acid/acetate buffer, 3.0 mmol L-1 SAPH, and 50% ethanol. Detection and quantitation limits were found to be 2.7 μg L-1 and 9.1 μg L-1, respectively. The upper limit of application was assessed through the limit of linearity which was set as 300 μg L-1. Intra-day repeatability and inter-day repeatability were evaluated showing an excellent precision for the fluorescence method (both < 5%). The method was sensitive enough for the satisfactory determination of aluminium in several bivalve mollusk samples both fresh and canned seafood. The results showed that commercial fresh wild products presented the smallest Al concentration (6-27 mg per 100 g dry weight), while bivalves preserved in cans the concentration was considerably higher (75 mg per 100 g dry weight). Thus, differences between Al concentration related to processing were identified. The study shows a simple, cost-effective and reliable tool for routine aluminium determination in seafood for food quality control.

Multi-elemental ionic liquid-based solvent bar micro-extraction of priority and emerging trace metallic pollutants (Cd, Ag, Pd) in natural waters

Transition metals Cd, Pd and Ag are toxic even at very low concentration. Cd is considered a priority substance; while, Pd and Ag are emerging pollutants. Membrane technologies have been applied for their extraction; however, they require important amounts of reagents, time and energy. Additionally, effective reagents for metal extraction in saline natural waters are limited. In this case, hollow fiber liquid phase micro-extraction with a configuration of solvent bar (SBME) using the ionic liquid Cyphos® 101 as extractant is proposed. Optimized conditions for SBME of Cd, Ag and Pd were 50% Cyphos® 101 in the organic solution, extraction time 30 min and 800 rpm stirring rate. Leaching was in all cases lower than 0.1%. Metallic concentrations were measured by flame atomic absorption spectroscopy. The method was applied to the extraction of Ag, Cd and Pd in natural water samples. Except for waste water, Pd extraction was higher than 90% in all cases. Cd (≈100%) and Ag (93-95%) offered their best results for saline samples. Concluding, the proposed system is a low cost and green methodology that allows a simple and fast extraction of trace pollutants such as Ag, Cd and Pd in different natural waters, including highly saline samples.