Screening of perfluorinated chemicals (PFCs) in various aquatic organisms

The aim of this study was to evaluate the occurrence of five perfluorinated chemicals (perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid) in aquatic organisms dwelling in either freshwater or marine ecosystems. Organisms selected were insect larvae, oysters, zebra mussels, sardines, and crabs, which are widespread in the environment and may represent potential bioindicators of exposure to PFCs. The study comprises the optimization of a solid–liquid extraction method and determination by high-performance liquid chromatography coupled to tandem mass spectrometry. Using spiked zebra mussels at 10 and 100 ng/g level, the method developed provided recoveries of 96% and 122%, and 82% to 116%, respectively, and a limit of detection between 0.07 and 0.22 ng/g ww. The method was highly sensitivity and robust to determine PFC compounds in a wide array of biological matrices, and no matrix interferents nor blank contamination was observed. Among organisms studied, none of the bivalves accumulated PFCs, and contrarily, insect larvae, followed by fish and crabs contained levels ranging from 0.23 to 144 ng/g ww of PFOS, from 0.14 to 4.3 ng/g ww of PFOA, and traces of PFNA and PFHxS. Assessment of the potential use of aquatic organisms for biomonitoring studies is further discussed.     

Windowed Green function method for wave scattering by periodic arrays of 2D obstacles

This paper introduces a novel boundary integral equation (BIE) method for the numerical solution of problems of planewave scattering by periodic line arrays of two-dimensional penetrable obstacles. Our approach is built upon a direct BIE formulation that leverages the simplicity of the free-space Green function but in turn entails evaluation of integrals over the unit-cell boundaries. Such integrals are here treated via the window Green function method. The windowing approximation together with a finite-rank operator correction—used to properly impose the Rayleigh radiation condition—yield a robust second-kind BIE that produces superalgebraically convergent solutions throughout the spectrum, including at the challenging Rayleigh–Wood anomalies. The corrected windowed BIE can be discretized by means of off-the-shelf Nyström and boundary element methods, and it leads to linear systems suitable for iterative linear algebra solvers as well as standard fast matrix–vector product algorithms. A variety of numerical examples demonstrate the accuracy and robustness of the proposed methodology.     

Energetics of lead(II), cadmium(II) and zinc(II) complexes with amino acids

The molar heat capacity and the standard (p ⁰ = 0.1 MPa) molar enthalpies of formation of the crystalline of bis(glycinate)lead(II), Pb(gly)₂; bis(dl-alaninate)lead(II), Pb(dl-ala)₂; bis(dl-valinate)lead(II), Pb(dl-val)₂; bis(dl-valinate)cadmium(II), Cd(dl-val)₂ and bis(dl-valinate)zinc(II), Zn(dl-val)₂, were determined, at T = 298.15 K, by differential scanning calorimetry, and high precision solution-reaction calorimetry, respectively. The standard molar enthalpies of formation of the complexes in the gaseous state, the mean molar metal–ligand dissociation enthalpies, M(II)–amino acid, \( \langle D_{\text{m}} \rangle \)(M–L), were derived and compared with analogous copper(II)–ligand and nickel(II)–ligand.θθ

M(II)–amino acid	\( \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \)(cr)/kJ mol?1
Bis(glycinate)lead(II), Pb(gly)2	?998.9 ± 1.9
Bis(dl-alaninate)lead(II), Pb(ala)2	?1048.7 ± 1.8
Bis(dl-valinate)lead(II), Pb(val)2	?1166.3 ± 2.5
Bis(dl-valinate)cadmium(II), Cd(val)2	?1243.7 ± 2.7
Bis(dl-valinate)zinc(II), Zn(val)2	?1306.1 ± 2.3

     

Adsorption of a reactive dye on chemically modified activated carbons--influence of pH

The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H2 flow at 700 degrees C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pH(pzc) of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.     

Pattern recognition for the analysis of polymeric materials

A new method of polymer classification is described involving dynamic mechanical analysis of polymer properties as temperature is changed. The method is based on the chemometric analysis of the damping factor (tan delta) as a function of temperature. In this study four polymer groups, namely, polypropylene, low density polyethylene, polystyrene and acrylonitrile-butadiene-styrene, each characterised by different grades, were studied. The aim is to distinguish polymer groups from each other. The polymers were studied over a temperature range of -50 degrees C until the minimum stiffness was reached, tan delta values were recorded approximately every 1.5 degrees . Principal components analysis was performed to visualise groupings and also for feature reduction prior to classification and clustering. Several clustering and classification methods were compared including k-means clustering, hierarchical cluster analysis, linear discriminant analysis, k-nearest neighbours, and class distances using both Euclidean and Mahalanobis measures. It is demonstrated that thermal analysis together with chemometrics provides excellent discrimination, representing a new approach for characterisation of polymers.     

Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis

A chiral separation method for glycidol enantiomers determination by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry was developed. Two chiral stationary phases, amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) and (S)-indoline-2-carboxylic acid and (R)-1-(α-naphthyl) ethylamine (SUMICHIRAL OA-4900) have been investigated. The effects of the mobile phase composition, elution program and column temperature were also studied. Under the best conditions: Chiralpak AD-H column, mobile phase composition n-hexane:ethanol (70:30, v/v), flow rate of 0.8 mL/min and 40 °C column temperature, a good resolution (Rs = 1.6) for both enantiomers has been achieved with an analysis time of 16 min. The method was found to be linear in the range from 100 to 500 ppm for both glycidol enantiomers with a good determination coefficient (r² higher than 0.99) and good precision. Limits of detection of 31 and 50 ppm for (R)-(+)-glycidol and (S)-(−)-glycidol, respectively, were obtained. The method was applied to the determination of the enantiomeric excess and yield obtained in a asymmetric epoxidation process of allyl alcohol with a chiral titanium-tartrate complex as catalyst.     

Existence results for quasilinear elliptic exterior problems involving convection term and nonlinear Robin boundary conditions

In this paper, the authors establish the existence of solutions for a class of elliptic exterior problems involving convection terms and nonlinear Robin boundary conditions. The proof of the result is made by combining Galerkin method with a priori estimates for this kind of problem.     

New synthesis strategies for effective functionalization of kaolinite and saponite with silylating agents

Functionalization of Brazilian São Simão kaolinite and Spanish Yunclillos saponite with the alkoxysilanes 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane is reported. The resulting hybrids were characterized by X-ray diffraction, thermal analysis, infrared absorption spectroscopy, and scanning electron microscopy, which demonstrated the effectiveness of the interlamellar grafting process. The X-ray diffractograms revealed incorporation of the alkoxide molecules into the interlayer space of the clays. The displacement of the stretching bands of interlayer hydroxyls in the infrared spectra of the modified kaolinites and the increased intensity of the Mg–OH vibrations in the spectra of the modified saponites confirmed the functionalization of the clays. The thermal behavior of the organoclays confirmed the stability of the hybrids, which was dependent on the clay used for preparation of the materials.     

Flow-injection determination of ammonia in kjeldahl digests by gas diffusion and conductometry

A flow injection/conductometric method is proposed for determing ammonia in solutions obtained from Kjeldahl digestion. The method is based on diffusion of ammonia through a PTFE membrane from an alkaline (NaOH/EDTA) medium to a deionized water stream. The change in conductance of the deionized water stream is proportional to the ammonia concentration present in the digest. The effects of flow parameters, temperature and potential interferences are reported. Approximately 100 samples can be injected per hour; the precision is about 1%. Results for total nitrogen in vegetable tissues, animal feeds and fertilizers are in good agreement with those obtained by the usual distillation/titration method.     

Synthesis,doping, and processing of high molecular weight poly(o-methoxyaniline)

High molecular weight poly(o-methoxyaniline) was synthesized using a novel method in which the polymerization occurs in the presence of a neutral salt. The molecular weight of the polymer was greatly affected by the quenching procedure employed to conclude the polymerization. Conventional doping of the base form of poly(o-methoxyaniline) produced a yellow coloration of the doping solution and polymer degradation. It was found that the molecular weight of the polymer decreased significantly after washing or doping with certain aqueous acid media. The gelation conditions of N-methyl pyrrolidinone (NMP) solutions and film preparation were also investigated for polymers of various molecular weights. The gelation time in NMP decreased drastically with the increase in the polymer molecular weight (the same for solution concentration and temperature), until a critical point was reached after which its decrease was very slow. Flexible, free-standing, and stretchable films were readily obtained from the higher molecular weight polymers. Good quality doped gel films with conductivity of up to 1 S/cm were obtained under optimized doping conditions. © 1994 John Wiley & Sons, Inc.