Volatility of compounds

Cross-media pollutant transfer through volatilization of compounds and absorption of chlorinated organics to wastewater particulates and sludge. 

There are a few cases in which the rules for the volatility of compounds, derived from geometrical considerations, do not hold. The halides of lithium, for example, have somewhat lower boiling points than expected it will be shown later that this discrepancy is... 

The influence of the penetration by the hydrogen ion on the volatility of compounds can be appreciated in another way. As long as the H ion is on the periphery of the Cl" ion, the molecule will, in many respects, resemble that of NaCl, possessing analogous properties, but if the positive H+ ion could penetrate the molecule so that it... 

Of the two techniques described here, simultaneous distillation extraction (SDE) is a more complete volatile extraction procedure that serves to obtain quantitative information on the compounds contained in a food. Volatile trapping is a partial extraction procedure that samples the vol a-tiles present in the headspace above a food, which are those with higher volatili ty. Extended trapping also induces additional volatilization of compounds initially contained in the food. 

If quantitative extraction is not necessary, some sample conditions may be adjusted to increase volatility of selective compounds. It is important to recognize that the selective nature of these changes in sample conditions affects the relative volatility of compounds, and thus distorts the amount of each compound that volatilizes. Thus, quantification of enhanced extractions is not truly representative of the sample s relative headspace. 

The best results were obtained with compound 21 that exhibited high vapor pressure and low decomposition temperature (<523 K). Various CVD conditions were applied and gave in all cases shiny, dark-brown deposits.43 XRD and XPS analyses of the deposits indicated the presence of a vanadium carbonitride phase with little contamination from oxygen and free carbon. The films were less adherent on steel substrates than on silicon ones. The steel substrates seemed to suffer corrosion due to the presence of Cl-containing species. We had noticed the same feature in the case of Cl-containing precursors to vanadium carbide. Therefore, in order to increase the volatility of compound 23 and to reduce the Cl content of the molecule, we prepared compounds 24 and 25. Unfortunately, the yields obtained in their syntheses were much too low to permit TG and CVD experiments. 

Up to now, only empirical methods can predict the volatility of compounds. These predictions represent an important part in the multiple step process of the chemical characterization of transactinide elements. The main steps in this process are ... 

The volatility of compound 160 is very low, but its chemical ionization mass spectrum exhibits a molecular ion peak. ... 

Because of the effects of the lanthanide contraction, both the atomic radii of Zr and Hf (1.45 and 1.44 A, respectively) and the radii of the Zr4+ and Hf4+ ions (0.74 and 0.75 A, respectively) are virtually identical. This has the effect of making the chemical behavior of the two elements extremely similar, more so than for any other pair of congeneric elements. The chemistry of hafnium has been studied less than that of zirconium but only small differences, e.g., in solubilities and volatilities of compounds, are to be expected or found. 

These gas ionisation sources have been described in Section 2.1.5 on mass spectrometry. They are particularly suitable for the analysis of mixtures of volatile and low molecular weight compounds (<800) such as hydrocarbons, essential oils and relatively nonpolar drugs. Chemical derivatisation, e.g. trimethylsilylation, can often be employed to increase the volatility of compounds containing polar functional groups (-OH, -COOH, -NH2 etc) so that GC-MS can be used. 

Carbohydrates can have a measurable influence on the release and perception of flavors. Carbohydrates change the volatility of compounds relative to water, but the effect depends on the interaction between the particular volatile molecule and the particular carbohydrate. As a general rule, carbohydrates, especially polysaccharides, decrease the volatility of compounds relative to water by a small to moderate amount, as a result of molecular interactions. However, some carbohydrates, especially the monosaccharides and disaccharides, exhibit a salting-out effect, causing an increase in volatility relative to water (Godshall, 1997). 

Ideally samples should be analyzed in situ or at the site of sampling in the field. If direct measurements are not possible or are too expensive, samples should be analyzed as soon as possible to avoid the need for preservation. However, samples cannot always be analyzed directly and they may have to be stored for so long that preservation is necessary. The preservation of water samples is covered in ISO standard 5667/3 (1985). The preservation methods described in this standard include time limits for sample storage and analysis specifications for container material prevention of exposure to light temperature control (2-5°C) pH control (addition of sulfuric, nitric, or phosphoric acid, or sodium hydroxide) addition of special reagents (e.g., ethylenediaminetetraacetic acid (EDTA), copper sulfate, zinc acetate, formaldehyde) to retard biological activity, hydrolysis of compounds and complexes and measures for reducing volatility of compounds and sorption effects. 

Vapor pressure curves (Gaggeler 1994 Turler 1996 Gartner et al. 1997) give a measure of the volatility of compounds. In O Fig. 20.4, the vapor pressure curves of the monomeric gas over the respective solids for Zr and Hf tetrachlorides and -bromides and for Nb and Ta pentachlorides and -bromides are shown, respectively. Also shown are vapor pressure curves for Nb and Ta oxytrichlorides. These curves are calculated using tabulated standard... 

The most obvious chemical compound of hassium suitable for its chemical separation is the tetroxide, HSO4, which is likely to be highly volatile. Zhuikov et al. (1986) have set up an online system in which radioactive Os recoils were thermalized in a gas mixture of 1.2 bar Ar + 2% O2 whereby volatile OSO4 was formed in situ and was transported without aerosols through a Teflon capillary to the detection device. This technique has been adapted (DiilLmann et al. 2002a Kirbach et al. 2002 von Zweidorf et al. 2002) in the preparation of the first chemical identification of Hs. The IVO technique developed by Kirbach et al. and DiilLmann et al. combines the in situ volatilization of compounds with their online detection in a narrow, 40 cm... 

Heterocyclcs have also been obtained by carbonylation of o/V/70-substituted nitro compounds, by using selenium in water as catalyst. This route seems to be limited by the toxicity and volatility of compounds such as H2SC and COSe. Besides 2-benzoxazolones (37) (cq. 17) [70] ... 

Derivative formation is of course of great importance when the combination of GC-MS is used and also in order to increase the volatility of compounds with low volatility. 

Differences in the volatility of compounds of the elements may influence relative recoveries during ashing procedures, and the selectivity and afBnity of Re and Tc on chromatographic resins under specific conditions may differ. ... 

Intermolecular interactions Dimeric cluster formation Combination of organic and inorganic moieties Contribution increased by the volatility of compounds... 

The TICs of the headspace volatiles of Ethiopia coffee bean (L23) adsorbed on the SPME fiber under static and dynamic conditions under the same GCMS conditions are shown in Fig. 3. The DH-SPME sampling resulted in acceptable peak intensity and a chromatographic profile, and the ratios of components adsorbed were different from those obtained by the SH-SPME sampling. The amount of peak area of 47 volatile compounds trapped under the dynamic condition was about 1.8 times that of volatiles trapped under the static condition (Table 1). Also, minor compounds reported as potent odorants of coffee, such as 4-hydroxy-2,5-dimethyl-3(2//)-furanone, 2-methoxyphenol, 4-ethenyl-2-methoxyphenol, and 2-ethyl-3,5-dimethylpyr-azine, were found to be present in higher concentrations in the dynamic headspace than in the static headspace. This chromatographic difference was considered to have resulted from additional volatilization of compounds induced by flowing inert gas above the sample [10]. 

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