Vapor-particle partitioning of hydrocarbons in Western Mediterranean urban and marine atmospheres

An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon.     

Novel approach for asymmetric synthesis of fluorinated beta-amino sulfones and allylic amines

[reaction: see text] Enantiomerically pure gamma-fluoroalkyl beta-amino sulfones are readily synthesized in three steps starting from fluorinated imidoyl chlorides and arylmethyl sulfones. A complementary two-step sequence starting from chiral fluorinated beta-amino sulfoxides has also been developed. To illustrate the application of this procedure, a new method for the synthesis of alpha-fluoroalkyl allylic amines in optically pure form involving a Julia methylenation-desulfonylation reaction is presented.     

Gas chromatographic-mass spectrometric analysis of urban-related aquatic and airborne volatile organic compounds. Study of the extracts obtained by water closed-loop stripping and air adsorption with charcoal and polyurethane foam

The distribution of volatile organic compounds (VOC) in urban-influenced air and river waters was investigated. The aquatic VOC were extracted with the closed-loop stripping technique (CLST) and the airborne compounds were studied using two methods, charcoal and polyurethane foam adsorption. In both types of samples, C1-C5 alkylbenzenes and n-alkanes constitute the two major VOC groups, and the presence of these groups indicates a predominance of petroleum products in these two environmental compartments. Chlorinated compounds such as polychlorobenzenes, polychloronaphthalenes and hexachlorobutadiene are abundant in water samples, whereas tetrachloroethene is the predominant chlorinated airborne VOC. The compounds collected with each sampling system can be described in terms of ranges of volatility. These ranges (expressed as mmHg vapour pressure at 25 degrees C) can be defined approximately as 140 (methylcyclopentane)-0.65 (n-undecane) for charcoal, 5.1 (n-nonane)-0.000061 (n-docosane) for polyurethane foam and 29 (toluene)-0.000029 (n-eicosane) for the CLST. Parallel air sampling with charcoal and polyurethane foam is therefore needed to cover a VOC range similar to that afforded by the CLST in water.     

The composition of volatile and particulate hydrocarbons in urban air

Summary The hydrocarbon composition of the particle and gas phases in the urban atmosphere has been studied by filtration and parallel adsorption on active charcoal and polyurethane foam (PUF). Gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS) have been used for the analysis of the organic matter extracts obtained with each system. In the case of the particle and PUF samples these extracts were fractionated into aliphatic and aromatic compounds. This approach has allowed to identify up to 247 hydrocarbon molecules showing that C0–C5 alkylbenzenes are the major compounds in the charcoal extracts whereas C14–C23 n-alkanes, C0–C4 alkylnaphthalenes, C0–C4 alkylbiphenyls and C3–C5 alkylbenzenes are those predominantly found in the PUF materials. The particles essentially contain C17–C38 n-alkanes and parent polycyclic aromatic hydrocarbons (PAH). These qualitative differences are paralleled by a progressive concentration decrease from the more to the less volatile hydrocarbons. Thus, the total charcoal extracts average 80 g/m³, the PUF compounds represent 4 /m³ and the particle hydrocarbons 0.7 g/m³. These latter airborne materials are essentially composed of petrogenic residues 0.6 g/m³ (aliphatic fraction) whereas the pyrolytic PAH only involve 0.08 g/m³.     

Distribution of Substituents in Methylcellulose

Abstract

The distribution of methyl groups in methylcelluloses (DS 1.7) has been determined. The partially methylated monosaccharides obtained on complete hydrolysis of methylcellulose were converted into alditols by reduction. They were identified as their acetates or trimethylsilyl ethers by gas-liquid chromatography-mass spectrometry and quantified by gas-liquid chromatography. In addition, ¹³C-nuclear magnetic resonance spectra of native and hydrolyzed methylcelluloses as well as the partially methylated alditols obtained by hydrolysis and reduction were analyzed. The main glucose methyl ethers obtained were in decreasing order 2,6-, 2,3,6-, 2-, 6-, and 2,3-. The 2-and 6-positions were occupied by methyl groups in 70.0 and 61.5%, respectively, while the 3-position contained only 37.4%. The GLC-MS method gave a more accurate determination of the distribution of methyl groups in methylcellulose compared to NMR spectroscopy.     

Discrimination of Beers by Cyclic Voltammetry Using a Single Carbon Screen-printed Electrode

A fast, simple and costless methodology without sample pre-treatment is proposed for the discrimination of beers. It is based on cyclic voltammetry (CV) using commercial carbon screen-printed electrodes (SPCE) and includes a correction of the signals measured with different SPCE units. Data are submitted to partial least squares discriminant analysis (PLS−DA) and support vector machine discriminant analysis (SVM−DA), which allow a reasonable classification of the beers. Also, CV data from beers can be used to predict their alcoholic degree by partial least squares (PLS) and artificial neural networks (ANN). In general, non-linear methods provide better results than linear ones.     

Ultrasonic study of wheat flour properties

In this work, the wheat flour properties are investigated using ultrasound techniques. Moreover, the flour samples were also characterized by means of well established techniques such as protein content, Alveograph and Mixolab®. A set of 35 dough samples, made of wheat flours with diverse physical and quality properties, were studied. The obtained results shown that ultrasound measurements can detect changes in the dough consistency induced by proteins and also by gelatinization of the starch. Furthermore, ultrasound measurements can be related to parameters indicative of the proteolytic degradation or softening of the dough due to protease activity. Thus, ultrasound can be considered a low cost and rapid tool, complementary to conventional test, for wheat flour characterization.