Aresatz Usobiaga

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.

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.

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.

Evolution of the Cannabinoid and Terpene Content during the Growth of Cannabis sativa Plants from Different Chemotypes

The evolution of major cannabinoids and terpenes during the growth of Cannabis sativa plants was studied. In this work, seven different plants were selected: three each from chemotypes I and III and one from chemotype II. Fifty clones of each mother plant were grown indoors under controlled conditions. Every week, three plants from each variety were cut and dried, and the leaves and flowers were analyzed separately. Eight major cannabinoids were analyzed via HPLC-DAD, and 28 terpenes were quantified using GC-FID and verified via GC-MS. The chemotypes of the plants, as defined by the tetrahydrocannabinolic acid/cannabidiolic acid (THCA/CBDA) ratio, were clear from the beginning and stable during growth. The concentrations of the major cannabinoids and terpenes were determined, and different patterns were found among the chemotypes. In particular, the plants from chemotypes II and III needed more time to reach peak production of THCA, CBDA, and monoterpenes. Differences in the cannabigerolic acid development among the different chemotypes and between monoterpene and sesquiterpene evolution patterns were also observed. Plants of different chemotypes were clearly differentiated by their terpene content, and characteristic terpenes of each chemotype were identified.

Solid-phase extraction combined with large volume injection-programmable temperature vaporization-gas chromatography-mass spectrometry for the multiresidue determination of priority and emerging organic pollutants in wastewater.

In the present work the simultaneous extraction for the multiresidue determination in wastewater samples of organic compounds such as polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), pesticides, polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PEs), alkylphenols (APs), bisphenol A (BPA) or hormones included in different lists of priority and emerging pollutants because of their action as endocrine disrupting compounds (EDCs) was developed. Different solid phase extraction (SPE) variables such as the nature of the solid phase (Oasis-HLC, C18 and Lichrolut), the sample volume, the addition of MeOH and NaCl, the pH of the water phase and the volume of the eluent solvent were optimized in order to analyze simultaneously the priority and emerging families of pollutants mentioned above. Good recoveries were obtained for Milli-Q water (80-120%), however, since the use of deuterated analogues and dilution of the sample did not correct the matrix effect, additional SPE clean-up step using Florisil® cartridges was necessary to obtain good results for wastewater samples (80-125%). In order to improve the limits of detection (LODs), large volume injection (LVI) using programmable temperature vaporizer (PTV) coupled to gas chromatography-mass spectrometry (GC-MS) was also optimized. Since analytes losses in the case of the most volatile congeners occurred during the derivatization step and no separation of the derivatized and the non-derivatized analytes was possible during SPE elution, two different injections were optimized for each analyte group. LODs were in good agreement with those found in the literature and relative standard deviations (RSDs) were in the 10-25% range for Milli-Q and 12-30% for wastewater samples. The method was finally applied to the determination of target analytes in three different wastewater treatment plants (WWTPs, Bakio, Gernika and Galindo (Spain)) and in one water purification plant (WPP) in Zornotza (Spain).

Microencapsulation and storage stability of polyphenols from Vitis vinifera grape wastes

Wine production wastes are an interesting source of natural polyphenols. In this work, wine wastes extracts were encapsulated through vibration nozzle microencapsulation using sodium alginate as polymer and calcium chloride as hardening reagent. An experimental design approach was used to obtain calcium-alginate microbeads with high polyphenol content and good morphological features. In this way, the effect of pressure, frequency, voltage and the distance to the gelling bath were optimized for two nozzles of 150 and 300 μm. Long-term stability of the microbeads was studied for 6 months taking into account different storage conditions: temperatures (4 °C and room temperature), in darkness and in presence of light, and the addition of chitosan to the gelling bath. Encapsulated polyphenols were found to be much more stable compared to free polyphenols regardless the encapsulation procedure and storage conditions. Moreover, slightly lower degradation rates were obtained when chitosan was added to the gelling bath.

Calibration and field test of the Polar Organic Chemical Integrative Samplers for the determination of 15 endocrine disrupting compounds in wastewater and river water with special focus on performance reference compounds (PRC).

In this work, home-made Polar Organic Chemical Integrative Samplers (POCIS) were studied for passive sampling of 15 endocrine disrupting compounds (4 alkylphenols and steroid hormones) in influent and effluent samples of wastewater treatment plants (WWTPs) as well as up- and downstream of the receiving river water. POCIS calibration at laboratory conditions was carried out using a continuous-flow calibration system. The influence of the exposure position of the POCIS within the calibration device, horizontal or vertical, to the water flow direction was evaluated. While the sampling rates of most of the target substances were not affected by the sampler position, for cis-ADT, E1, E2 and E3, the vertical position provided the highest analyte accumulation. Hence, the POCIS samplers were preferably exposed vertical to the water flow in overall experiments. Using the continuous-flow calibration device, lab-based sampling rates were determined for all the target compounds (RSBPA = 0.0326 L/d; RScisADT = 0.0800 L/d, RSE1 = 0.0398 L/d, RSEQ = 0.0516 L/d, RSTT = 0.0745 L/d, RSE2 = 0.0585 L/d, RSEE2 = 0.0406 L/d, RSNT = 0.0846 L/d, RSPG = 0.0478 L/d and RSE3 = 0.1468 L/d), except for DES, MeEE2, 4tOP, 4OP, 4NPs, where the uptake after 14 days POCIS exposure was found to be insignificant or indicated a no linear behaviour. Recoveries from POCIS extractions were in the range between 71 and 152% for most of the target analytes except for DES and E3 with around 59%. Good precision of the sampling procedure up till 20% was observed and limits of detection were at ng/L level. Two deuterated compounds ([(2)H3]-E2 and [(2)H4]-EQ) were successfully tested as performance reference compounds (PRC, [Formula: see text] = 0.0507 L/d and [Formula: see text] = 0.0543 L/d)). Finally, the POCIS samplers were tested for monitoring EDCs at two wastewater treatment plants, in Halle and Leipzig (Germany). BPA, E1, EQ, E2, MeEE2, NT, EE2, PG and E3 were quantified and their time-weighted average concentrations calculated on the basis of the lab-derived sampling rates were compared with the results based on conventional grab samples. While the influent concentration of BPA, cisADT, E1, TT, PG, EE2 reached the μg/L level, the rest of the target analytes were determined at ng/L. The analyte concentrations in the effluent never exceed ng/L level except for BPA. The concentration determined by spot sampling was partially lower (BPA, E1, TT) or comparable (EQ, E2, EE2, PG, E3) to the concentration obtained by POCIS using performance reference compounds (PRC).

Targeting the endocannabinoid system : future therapeutic strategies

The endocannabinoid system (ECS) is involved in many physiological regulation pathways in the human body, which makes this system the target of many drugs and therapies. In this review, we highlight the latest studies regarding the role of the ECS and the drugs that target it, with a particular focus on the basis for the discovery of new cannabinoid-based drugs. In addition, we propose some key steps, such as the creation of a cannabinoid-receptor interaction matrix (CRIM) and the use of metabolomics, toward the development of improved and more specific drugs for each relevant disease.

Application of the electrical conductivity of concentrated electrolyte solutions to industrial process control and design: from experimental measurement towards prediction through modelling

Different aspects of the conductivity of concentrated electrolyte solutions and their application to design and control of chemical processes are discussed and reviewed, with particular focus on the work of our research group during the last few years. An automated system based on the electrodeless conductivity technique for the measurement of the electrical conductivity of solutions as the basis of a titration strategy is described. The inadequacy of classical calibration methods when high conductivities are to be measured is highlighted and an alternative methodology is proposed. Our measurements on specific concentrated systems of interest in industrial applications and the development of general methodologies to treat experimental conductivity data at constant or varying temperature in order to get comprehensive inter- and extrapolation mathematical models are summarised. Theoretical approaches to explain the variability of conductivity data of electrolyte solutions with the solute concentration as well as the deviations from ideality found at higher concentrations are reviewed and critically evaluated. Solutions of mixed electrolytes are treated in a similar fashion.