Development of solid-phase extraction and solid-phase microextraction methods for the determination of chlorophenols in cork macerate and wine samples

Tri-, tetra- and pentachlorophenol (TCP, TeCP and PCP) can be considered the precursors in the formation of corresponding chloroanisoles, known to be powerful odorants in corks and wine. Determining the presence of these chlorophenolic compounds in cork soaking solutions (ethanol/water mixtures, 12% (v/v) ethanol used for cork quality control testing), or in wine can be achieved by acetylation/gas chromatography electron-capture detection. In order to reach the required sensitivity, a previous preconcentration step is necessary. Solid-phase extraction (SPE) and headspace solid-phase microextraction (HS-SPME) have given good results for the preconcentration of TCP, TeCP and PCP in such matrices. The use of Oasis HLB cartridges gives acceptable recoveries for the three compounds when different volumes (50-250 mL) of cork macerate with concentrations ranging from 20 to 150 ng/L are processed. Preconcentration based on HS-SPME has also been optimised with a 100 microm polydimethylsiloxane fibre and in situ derivatization. The HS-SPME method allows chlorophenols in a cork soaking solution and in wine to be determined with a limit of detection of 1 ng/L for each compound (in cork macerate) and a repeatability of around 0.5%-5% (n=8) for a concentration level of 30 ng/L.     

Highly selective solid-phase extraction and large volume injection for the robust gas chromatography-mass spectrometric analysis of TCA and TBA in wines

A reliable solid-phase extraction (SPE) method for the simultaneous determination of 2,4,6-trichloroanisole (TCA) and 2,4,6-tribromoanisole (TBA) in wines has been developed. In the proposed procedure 50 mL of wine are extracted in a 1 mL cartridge filled with 50 mg of LiChrolut EN resins. Most wine volatiles are washed up with 12.5 mL of a water:methanol solution (70%, v/v) containing 1% of NaHCO3. Analytes are further eluted with 0.6 mL of dichloromethane. A 40 microL aliquot of this extract is directly injected into a PTV injector operated in the solvent split mode, and analysed by gas chromatography (GC)-ion trap mass spectrometry using the selected ion storage mode. The solid-phase extraction, including sample volume and rinsing and elution solvents, and the large volume GC injection have been carefully evaluated and optimized. The resulting method is precise (RSD (%) < 6% at 100 ng L(-1)), sensitive (LOD were 0.2 and 0.4 ng/L for TCA and TBA, respectively), robust (the absolute recoveries of both analytes are higher than 80% and consistent wine to wine) and friendly to the GC-MS system (the extract is clean, simple and free from non-volatiles).     

Controlled Formation of Polymer Nanocapsules with High Diffusion‐Barrier Properties and Prediction of Encapsulation Efficiency

Polymer nanocapsules with high diffusion‐barrier performance were designed following simple thermodynamic considerations. Hindered diffusion of the enclosed material leads to high encapsulation efficiencies (EEs), which was demonstrated based on the encapsulation of highly volatile compounds of different chemical natures. Low interactions between core and shell materials are key factors to achieve phase separation and a high diffusion barrier of the resulting polymeric shell. These interactions can be characterized and quantified using the Hansen solubility parameters. A systematic study of our copolymer system revealed a linear relationship between the Hansen parameter for hydrogen bonding (δ_h) and encapsulation efficiencies which enables the prediction of encapsulated amounts for any material. Furthermore EEs of poorly encapsulated materials can be increased by mixing them with a mediator compound to give lower overall δ_h values.     

Impact of correlation structure on drainage in open rough walled fractures

The spatial correlation structure of heterogeneous parameters plays an important role in upscaling of many flow and transport processes in porous media and fractures. We analyze upscaling of a slow drainage process in a horizontal open rough walled fracture. The applicability of upscaled continuum models for this kind of flow process is discussed. We consider two different fracture aperture distributions with different spatial correlation properties. One is described by a slowly decaying, the other one by a Gaussian autocovariance. The flow process is modelled using an invasion percolation model, which takes the in plane curvature of the fluid cluster into account. Results are compared to laboratory experiments in artificial plexiglas fractures. Different averaging procedures are tested in order to assess the applicability of continuum models. Independently of the correlation structure of the fracture aperture field, spatial averages do not converge to a continuum formulation. Ensemble averages do converge, however, they only give probabilistic information and are not applicable to model drainage in a fracture.     

Synthesis and polymerization of 5‐(methacrylamido)tetrazole,a water‐soluble acidic monomer

The reaction of methacryloyl chloride with 5‐aminotetrazole gave the polymerizable methacrylamide derivative 5‐(methacrylamido)tetrazole ( 4 ) in one step. The monomer had an acidic tetrazole group with a pK_a value of 4.50 ± 0.01 in water methanol (2:1). Radical polymerization proceeded smoothly in dimethyl formamide or, after the conversion of monomer 4 into sodium salt 4‐Na , even in water. A superabsorbent polymer gel was obtained by the copolymerization of 4‐Na and 0.08 mol % N,N′‐methylenebisacrylamide. Its water absorbency was about 200 g of water/g of polymer, although the extractable sol content of the gel turned out to be high. The consumption of 4‐Na and acrylamide (as a model compound for the crosslinker) during a radical polymerization at 57 °C in D₂O was followed by ¹H NMR spectroscopy. Fitting the changes in the monomer concentration to the integrated form of the copolymerization equation gave the reactivity ratios r _4‐Na = 1.10 ± 0.05 and r_acrylamide = 0.45 ± 0.02, which did not differ much from those of an ideal copolymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4333–4343, 2002     

Assays on the simultaneous determination and elimination of chloroanisoles and chlorophenols from contaminated cork samples

A method for the simultaneous determination of the chloroanisoles and chlorophenols in cork samples with gas chromatography has been evaluated in view to its application. All the stages of the suggested procedure have been submitted to an in-depth examination using spiked ground corks. The recoveries of the method, which involves a simultaneous extraction with n-pentane followed by a second extraction using an aqueous basic solution where the phenolic derivates are transferred and, subsequently, derivatised, have been satisfactory for the all analytes at the studied spiking concentration levels. Good precision data and limits of detection between 1 ng/g and 2 ng/g were obtained for almost all compounds. As real samples, naturally contaminated cork slabs taken from different sources have been analysed, showing the presence of 2,4,6-trichloroanisole (TCA) and, in lesser extent, its direct precursor, 2,4,6-trichlorophenol (TCP). Removal studies have been performed by washing these tainted cork slabs with different solutions: Milli-Q water, sodium hydroxide and commercial products. Sodium hydroxide solutions have led to better analyte elimination, and the complete removal of TCP from the cork has been accomplished together with 72% of TCA reduction has been achieved.     

"Kinetic NMR titration": including chemical shift information in the kinetic analysis of supramolecular reaction systems such as organic replicators

Efficient harvesting of kinetic and thermodynamic information in supramolecular reaction systems comes from kinetic NMR titration, that is, the combined analysis of NMR integrals and chemical shifts. The method is introduced using a minimal self-replicating system studied at various temperatures.