Selection criteria volatility

The impact of volatile gas emissions from wood-based panels on the indoor environment is attracting more and more attention. In several cases the emissions to the indoor air have become an essential product selection criterion for both the... 

Reliable analytical methods are available for determination of many volatile nitrosamines at concentrations of 0.1 to 10 ppb in a variety of environmental and biological samples. Most methods employ distillation, extraction, an optional cleanup step, concentration, and final separation by gas chromatography (GC). Use of the highly specific Thermal Energy Analyzer (TEA) as a GC detector affords simplification of sample handling and cleanup without sacrifice of selectivity or sensitivity. Mass spectrometry (MS) is usually employed to confirm the identity of nitrosamines. Utilization of the mass spectrometer s capability to provide quantitative data affords additional confirmatory evidence and quantitative confirmation should be a required criterion of environmental sample analysis. Artifactual formation of nitrosamines continues to be a problem, especially at low levels (0.1 to 1 ppb), and precautions must be taken, such as addition of sulfamic acid or other nitrosation inhibitors. The efficacy of measures for prevention of artifactual nitrosamine formation should be evaluated in each type of sample examined. 

Most explosive detection equipments do not truly detect explosive vapour, rather they key on minute particles of the explosive [11]. The reason for this is that most explosives have very low vapour pressure, and low vapour pressures are rather difficult to measure. Methods based on mass loss or the direct measurement of tiny pressures are particularly prone to the influence of trace impurities of more volatile substances. Consequendy, the values reported in the literature exhibit a high degree of scatter. To add to the confusion, difierent units of measurement are used. In general, measurements involving chemical determination of the amount of the specific compound in the vapour phase are to be preferred. If several difierent values are reported, and there is no better criterion for selection, it is probably best to take the lowest value. 

In an attempt to provide further information relative to the validity of the diffusion mechanism, a typical set of results was selected from the isothermal release work, and the volume of volatile matter released was plotted against the square root of time. For a pure diffusion process such a plot should be almost linear initially (4) whereas for a true logarithmic time law, dVt/dt should tend to infinity for very small values of t. Figure 12 shows that by this criterion the rate controlling mechanism appears to be diffusion and not chemisorption. The fact that the curve does not pass through the origin is undoubtedly caused by the fact that it was not possible to heat the sample to... 

The particular absorber to be used in a given application depends on several factors. One important criterion is whether the absorber will strongly absorb that portion of the ultraviolet spectrum responsible for degradation of the plastic under consideration. Compatibility, volatility, thermal stability, and interactions with other additives and fillers are other items that must be considered. When used in food wrappings, Food and Drug Administration approval must be obtained. While one or more of these considerations may rule out a given stabilizer or influence llie choice of one class over another, the final selection must await the results of extensive accelerated and long-term tests. 

HCN is a volatile liqmd exothermic reaction, can occur spontaneously) and its toxicity, make its use and storage particularly hazardous. It may, however, be stabilized by adding traces of i osphoric acid or SOj. It is also noteworthy that carbon monoxide is at least as toxic as HCN. although this factor is not an important criterion in the selection of one of these two starting materials for a synthesis. The development of a COj -based chemistry is, how ever, particularly advantageous from this point of view. 

Several criteria must be considered in the selection of the diluent solvent. The first one is biocompatibility, that is, the solvent must not be toxic to the biodegrading microorganism [10]. The second criterion is the resistance to biodegradation and/or utilization by the active microorganism used, that is, so-caUed (non)bioavailability [8]. Third criterion is the favorable mass-transfer characteristics for the biodegraded pollutant [1], and the fourth criterion is the mutual immiscibility of the diluent with the treated waste-water [1]. The fifth criterion is the hmited volatility of the diluent [11]. 

J.A. Pino, D. Castro, P. Fito, J. Barat, and F. Lopez, Multivariate statistical analysis of volatile compounds as a criterion for selecting technological parameters in the osmotic dehydration of pineapple, J. Food Qual., 22 653 (1999). 

Theoretically, other acids, such as phosphoric acid or hydrochloric acid, can also be used, because these can also positively influence selectivity. The reason for their rare use is, in the case of hydrochloric acid, its high potential for corrosion, and phosphates are not volatile, which is an exclusion criterion in the case of MS or preparative apphcations. 

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