Nestor Etxebarria

Stir-bar sorptive extraction: A view on method optimisation, novel applications, limitations and potential solutions

Introduced in 1999 as a novel solventless sample preparation method, stir-bar sorptive extraction (SBSE) has become a popular analytical technique for the pre-concentration of organic compounds into a polydimethylsiloxane (PDMS)-coated stir-bar. In the last 10 years, hundreds of applications in the environmental, food and biomedical fields can be found in the literature. However, only PDMS-coated stir-bars are commercially available, which reduces the applicability of SBSE to the extraction of the non-polar compounds due to the poor extractability of more polar analytes. In this review, a view on method optimisation, limitations, potential solutions such as in-house coatings and derivatisation and novel applications in multi-residue analysis and passive sampling are revised.

MultiSimplex optimisation of the solid-phase microextraction-gas chromatographic-mass spectrometric determination of polycyclic aromatic hydrocarbons, polychlorinated biphenyls and phthalates from water samples

Solid-phase microextraction coupled to GC-MS was optimised for the determination of polycyclic aromatic hydrocarbons (PAHs), phthalate esters and polychlorinated biphenyls (PCBs) in water samples. A 30-microm polydimethylsiloxane fiber was immersed in a 30-ml water sample that contained the analytes of interest (PAHs, PCBs and phthalate esters) and the variables studied were extraction time (15-60 min), extraction temperature (30-90 degrees C), desorption time (1-5 min), desorption temperature (220-270 degrees C) and the addition of sodium chloride (0-9 g). The MultiSimplex programme based on the simplex algorithm was used to establish the optimal conditions. MultiSimplex allowed the simultaneous study of the variables mentioned above and considered the answers of all types of compounds studied in this work. Thus, the optimal conditions obtained allowed the simultaneous determination of PAHs, phthalate esters and PCBs. Furthermore, the accuracy and repeatability of the developed method were calculated from water samples spiked at known concentrations of the analytes. Finally, the optimised method was used to analyse water samples from different sampling points of the Urdaibai and Nerbioi-Ibaizabal estuaries (Biscay, Spain).

Distribution and bioaccumulation of PAHs in the UNESCO protected natural reserve of Urdaibai, Bay of Biscay.

Along 10 campaigns, from June 2002 to September 2004, the concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were measured in sediments and oysters (Crassostrea sp.) taken from four sites in the Unesco protected natural reserve of Urdaibai (Basque Country, Bay of Biscay). Total PAH concentration ranged from 0.7 to 140 microg kg(-1) (dw) in the case of sediments, and from 300 to 1400 microg kg(-1) (dw) in the case of oysters. During this study, the coast of the Bay of Biscay was severely affected by the Prestige oil spill (November 2002). Presumably, as a consequence of this accident, both spatial and temporal variations of the PAHs, as well as the sources of the PAHs were affected by the oil spill, and this effect was observed in the total concentrations and, especially, in several diagnostic ratios and in multivariate data analysis. Finally, both BAF (bioaccumulation factor) and BSAF (biota-sediment accumulation factor) parameters were calculated to conclude that particulate matter seems to be the most favourable uptake pathway of PAHs in oysters from this estuary.

Comparison of accelerated solvent extraction with microwave-assisted extraction and Soxhlet for the extraction of chlorinated biphenyls in soil samples

Abstract The extraction and determination of chlorinated biphenyls (CBs) in soils and solid wastes is an ongoing subject of study. This is an overview article that compares the microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) techniques. The extraction of CBs by ASE has been optimised taking into account the variation of pressure, temperature and extraction time by means of experimental design and the Simplex approach. The recoveries obtained under the optimum conditions are compared and discussed with those obtained from MAE and Soxhlet extractions.

Combined use of native and caged mussels to assess biological effects of pollution through the integrative biomarker approach.

Native and caged mussels were used in combination for the monitoring of pollution biological effects through an integrative biomarker approach. Mussels (Mytilus galloprovincialis) were deployed in cages in two well-known model localities with different pollution levels in the Basque coast. After 3 weeks caged and native mussels were collected from each site and a suite of effect and exposure biomarkers (from molecular/cellular to organism level) was applied and chemical contaminants (metals, PAHs, PCBs, phthalates and nonylphenol ethoxylates) were analytically determined. Integrative biomarker indices and pollutant indices of tissues were calculated. Several biomarkers used herein responded similarly in native and caged mussels, whereas others exhibited significant differences. Overall, biomarkers in-a-suite depicted site-specific profiles useful for the diagnostic of mussel health status and therefore for ecosystem health assessment in marine pollution biomonitoring. On the other hand, biomarkers and bioaccumulation exhibited different response times, which was especially evident when comparing biomarker and pollutant indices of tissues. The suite of biomarkers was more sensitive after caging (short-term response), whereas tissue pollutant concentrations were more sensitive in native mussels (long-term response). Thus, the combination of native and caged mussels is highly recommended to monitor biological effects of pollution in mussels through the integrative biomarker approach, especially in chronically polluted sites.

Simultaneous speciation of methylmercury and butyltin species in environmental samples by headspace-stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry

In this work, making use of experimental designs, headspace-stir bar sorptive extraction (HS-SBSE) followed by thermal desorption (TD) coupled to a gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of mercury and tin organometallic compounds present in surface water, sediment and biological tissue was optimized. All solid samples require a previous extraction typically done with diluted HCl or KOH/methanol solutions, and the derivatization, in all the cases, of the organometallic compounds with NaBEt(4). As a consequence, the preconcentration step was carried out in a 0.1 mol L(-1) HOAc/NaOAc buffer solution, with 0.1% (m/v) of NaBEt(4), without the addition of NaCl as a salting out reagent, and with the stir bar (20 mm x 1 mm) located in the headspace (HS). In addition, the desorption step required the following conditions: 250 degrees C (desorption temperature), 15 min (desorption time), 14.1 psi (approximately 97.2 kPa) (vent pressure) and 75 mL min(-1) (vent flow). Finally, to assure the extraction of all the analytes under equilibrium, 5h are required. Inorganic mercury (Hg(2+)) and tripropyltin (TPrT) were used as internal standards to correct for variations in the extraction, derivatization and detection steps. The resulting method provides precise (4-17%) and accurate (against four certified reference materials) results in the ng L(-1) and pg g(-1) range concentrations with recoveries within 80-120% for water samples. The proposed methodology is currently applied in the speciation analysis of specimens obtained in different estuarine sites of the Basque Coast.

Simultaneous preconcentration of a wide variety of organic pollutants in water samples. Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction.

Stir bar soptive extraction (SBSE) coupled to thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) and membrane-assisted solvent extraction (MASE) coupled to large volume injection-programmed temperature vaporisation-GC-MS (LVI-PTV-GC-MS) were optimised for the simultaneous determination of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalate esters (PEs), nonylphenols (NPs), polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in water samples. In the case of SBSE-TD, variables affecting the extraction (extraction time, addition of sodium chloride or methanol and sample volume) and desorption (cryofocusing temperature, desorption time and temperature, vent pressure and desorption flow) were fitted for the simultaneous determination. The extraction solvent nature (n-hexane, cyclohexane, n-heptane, ethyl acetate, toluene, dichloromethane or cyclohexane:ethyl acetate mixtures), as well as the addition of methanol (0-30%) and sodium chloride (0-20%), the extraction temperature (30-60 degrees C), shaking speed (250-750 rpm) and extraction time (5-150 min) were studied for the simultaneous membrane-assisted preconcentration. Finally, PTV-LVI variables such as injection volume (100-600 microL), injection speed (10-40 microL s(-1)), vent pressure (0-12.7 psi), vent time (0.05-0.8 min), vent flow (30-80 mL min(-1)), cryofocusing temperature (20-70 degrees C), split flow (20-100 mL min(-1)) and split time (1-5 min) were optimised. The optimisation was carried out by means of experimental design approaches in most of the cases. Precision (approximately 3-19% for both SBSE-TD and MASE-LVI-PTV), accuracy (approximately 80-120% for both SBSE-TD and MASE-LVI-PTV), limits of detection (LoDs) (0.1-222 ng L(-1) for MASE-LVI-PTV and 0.03-20.4 ng L(-1) for SBSE-TD in dependence of substance) and linearity (from 25 ng L(-1) up to at least 500 ng L(-1) for both procedures) were established for both procedures. Finally, the developed methods were applied to the determination of the free concentrations of PAHs, PCBs, PEs, NPs, PBBs and PBDEs in natural water samples (estuarine water and sea water) from the Bilbao estuary (Northern Spain) and comparable results were obtained with both procedures.

Analytical diagnosis methodology to evaluate nitrate impact on historical building materials.

Nitrate salts have become of greater importance in the decay of materials from historical buildings due to changes in the environment. This work presents an analytical diagnosis methodology to evaluate the impact of nitrate salts in mortars and bricks, combining noninvasive and microdestructive analytical techniques together with chemometric and thermodynamic data analyses. The impact of nitrate salts cannot be well ascertained if other soluble salts are not taken into account. Therefore, the principal results from this work relate to nitrate salts but some results for other kinds of salts are included. Data from Raman microprobe spectroscopy and micro X-ray fluorescence (μ-XRF) are used to characterise the original composition and a first approximation of the nature of the decay compounds, mainly nitrates. The soluble salts are extracted and the anions and cations are quantified by means of ion chromatography with conductimetric detection for anions/cations and inductively coupled plasma mass spectrometry (ICP/MS) for cations. The values obtained allow two different data treatments to be applied. First, chemometric analysis is carried out to search for correlations among anions and cations. Second, thermodynamic modelling with the RUNSALT program is performed to search for environmental conditions of soluble salt formation. All the results are finally used to diagnose the impact of nitrates.

Comparison of microwave-assisted extraction and Soxhlet extraction for phenols in soil samples using experimental designs

A study and comparison of microwave-assisted extraction (MAE) and Soxhlet extraction for five phenols (phenol, 2-chlorophenol, 2-methylphenol, 2-nitrophenol and 2,4-dichlorophenol) in soils was carried out in order to establish a comparative analysis between the two techniques under their optimum conditions. The optimisation of both the MAE and Soxhlet extraction methods was achieved using experimental designs. The parameters studied were pressure inside the extraction vessel, extraction time, percentage of microwave power, solvent volume and percentage (v/v) of acetone in an acetone–hexane mixture for MAE and extraction time and percentage (v/v) of acetone in an acetone–hexane mixture for Soxhlet extraction. The simplex method was also used for obtaining the optimum conditions in some cases. The extracts were analysed by GC–MS or GC–FID.

Development of a focused ultrasonic-assisted extraction of polycyclic aromatic hydrocarbons in marine sediment and mussel samples.

Focused ultrasonic-assisted extraction (FUSE) is a new and particular technique based on the cavitation effect. In this work, the focused ultrasound assisted extraction was studied and developed for the extraction of polycyclic aromatic hydrocarbons from marine sediments and mussel tissues. The variables influencing the extraction (amplitude of the ultrasound pulse, the extraction time and the solvent) were studied by a full factorial design and a central composite design. As a result, flat response surfaces were obtained and the most convenient conditions were 45% of ultrasound amplitude, 120s of extraction time and 5 mL of acetone. Both accuracy and precision of the method were evaluated by means of two certified reference materials (marine sediment and mussel tissue) and the results were also compared to those obtained by microwave assisted extraction.