Volatiles characterization

Another measurement characterizing volatility is that of vapor pressure. 

The absolute amount of product resulting from solid-phase synthesis can often be readily determined by 1H NMR with an internal standard or, less efficiently, by purification of the product followed by weighing and full characterization. Volatile samples can be cleaved with a calibrated mixture of hexamethyldisiloxane/TFA/CDCl3, from which 1H NMR spectra can be recorded directly [16]. In our laboratory, we use DMSO-dg as solvent and DMSO-internal standard for yield determination by 1H NMR. The weight of crude products obtained from solid-phase synthesis is generally unsuitable for estimating the true yield, because these products are often contaminated with significant amounts of salts, which lead to overestimation of the yield. 

These properties, which characterize volatility, also determine the concentration of the substance which can be achieved in the vapor phase and is thus available for uptake by inhalation. Volatile, low boiling point substances are thus more readily absorbed in the lung. 

During biomass and fuel burning, a complex mixture of ill-characterized volatile organic matter are released into the atmosphere (Andreae and Merlet, 2001). It contributes to the formation of aerosols and fine particles of sizes up to 100 pm. After an estimated lifetime of 7.9 days (Cook and Wilson, 1996), they are either degraded or are removed from the atmosphere by precipitation. However, they can be transported a considerable distance. For example, boreal forest fires contribute substantially to atmospheric BC in the Arctic (Cook and Wilson, 1996), and Antarctica receives BC from biomass burning in the tropics (Wolff and Cachier, 1998). On a global scale the amount of atmospheric emission is estimated with 5-6Tg BC yr 1,... 

Almost a decade before the term pheromone was coined, Roth and Willis (1952) conducted seminal experiments that characterized volatile and contact pheromones in cockroaches. Louis Roth s research integrated studies of endocrinology and behavior, and the influence of this approach was reflected in Barth s early articulation of the interplay between the endocrine system and sexual behavior. In later years cockroaches continued to serve as important models for invertebrate endocrinology (Scharrer, 1987 Tobe and Stay, 1985), but research on pheromones lagged, in part due to technical difficulties in sex pheromone identification. Below, we highlight some of the many issues yet to be resolved in the physiological and behavioral regulation of sex pheromone production and emission in cockroaches. 

The purpose of this investigation was to characterize volatiles and study their biogenesis in stalk of burley tobacco and wheat during active growth. A comparision was made of volatile compounds obtained by steam distillation and headspace... 

Although stress MS and the entire concept of a thermal-mechanical stress correlation may be in error, stress MS studies may have an even greater potential to help characterize volatile compounds trapped in or indigenous to otherwise intractable materials such as composites. 

Infrared spectroscopy can be used to perform qualitative analysis of gases. Pierson et al. (1956) have given a chart to be used for this purpose. Also, infrared spectroscopy and gas chromatography are a useful combination for characterizing volatile substances (see Appendix 1). Sometimes fractions from a vapor fractometer are collected as vapors in a gas cell. White et al. (1959) have described a microgas cell of 1 m path for use with a beam condenser to observe the spectra of gas chromatographic fractions less than 0.05 % of the total charge. 

Karl, T., Jobson, T., Kuster, W.C., Williams, E., Stutz, I, Shelter, R., Hall, S.R., Goldan, R, Fehsenfeld, E, Lindinger, W. (2003) Use of proton-transfer-reaction mass spectrometry to characterize volatile organic compound sources at the La Porte super site during the Texas Air Quality Study 2000. Journal of Geophysical Research-Atmospheres, 108,4508. 

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