Volatile additives, effect

The mantle viscosity which controls much of the dynamics of mantle plumes is not well known (Watson and Mackenzie 1991 Hauri et al. 1994). There are also additional effects such as when the mantle contains even small amounts of volatiles, as these volatiles will significantly lower the viscosity of the mantle (Hirth and Kolhstedt 1996). Once the volatiles are extracted, the increased viscosity will slow down the upwelling mantle (Ito et al. 1999). 

Females of the cowpea weevil, Callosobruchus maculatus, release a male attracting pheromone from the tip of their abdomen. The volatile signal contains five unsaturated, branched C8-acids 208-212 [376,377]. Individual compounds proved to be active while mixtures showed additive effects. Similarly, compounds 208 and 209 have been identified as the female produced sex pheromone of C. subinnotatus [378], while 209 had been described as the sex pheromone of C. analis [379]. However, GC-MS analyses of female produced volatiles of C. analis failed to detect any of the C. maculatus compounds, but did find an unidentified C8-acid with a retention time different from any of the C. maculatus acids [377]. 

The performance of the FBI can be enhanced by the use of (volatile) additives, such as ammonium acetate, formate, or oxalate, to the mobile phase [92]. They are assumed to act as carriers. Similarly, the use of additives with structures related to the target analyte structures, e.g., phenoxyacetic acid in the analysis of chlorophenoxyacetic acids, was evaluated as well [93]. The carrier effects, exerted by either mobile-phase additives, coeluting compounds, and/or isotopically-labelled standards, is not really understood from a mechanistic point of view. It caimot be applied to consistently enhance the performance for some compounds it works fine, while for others no effects are observed. 

The most widely applied LC method for the separation of peptides and proteins is reversed-phase LC (RPLC). A typical mobile-phase composition is an acetonitrile-water gradient with a fixed concentration of TFA (typically 0.05-0.5%). TEA acts as an ion-pairing agent enhancing the retention of peptides and proteins, but also masks secondary interactions with the silica-based stationary phase. TFA is a volatile additive, but due to its ion-pairing properties and effect on the surface tension, it may significantly suppress the ESI response in positive-ion mode. 

The odour intensities of volatiles showing similar odour qualities are partially additive [68]. To substantiate such additive effects, three groups of odorants (terpene hydrocarbons, esters or aldehydes) were omitted from the aroma model for orange juice. For all groups, a significant difference from the complete model was observed (Table 6.39). Omission of esters nos. 12,14 and 15 with ethyl butanoate (no. 13) still present was clearly detectable. This indicates that the fruity quality in the odour profile is enhanced by additive effects. In contrast, no difference was perceivable when (R)-a-pinene (no. 17) and myrcene (no. 18) were omitted. The concentration of the odorants in juice differs depending on the variety. Thus, the weaker citrus note of Navel oranges compared with the above discussed variety Valencia late is due to a 70% lower content of (R)-limonene [67]. 

A. E. Bergles and L. S. Scarola, Effect of a Volatile Additive on the Critical Heat Flux for Surface Boiling of Water in Tubes, Chem. Eng. Sci. (21) 721-723,1966. 

Compared with the samples typically separated by supercritical fluid chromatography most solvents are significantly more volatile and can be removed from the sample by evaporation in a short open tube or packed precolumn [174-178]. Solventless injection requires only minor modification to a standard rotary injector, either addition of a second valve or tee piece and a precolumn. This allows sequential programming of the independent processes of solvent removal and sample deposition in the precolumn followed by dissolution of the sample in the mobile phase and its transport to the column for refocusing. Quite large solvent volumes (hundreds of p,l) can be handled in this way, but typically smaller volumes are used. The only real limitation to solventless injection is that the volatility difference between the sample and solvent must be sufficient for effective removal of the solvent without loss of sample. In addition, effective sample focusing at the head of the column is required to maintain an acceptable separation... 

Ozone Gas Can attack almost all additives. Effective against Very reactive and volatile. 

However, due to its volatility the effect of formaldehyde can be short lived, especially when used in warm products or in those stored at elevated temperature. In addition it will lose its activity in the presence of some organic materials and has more recently been shown to cause coagulation of certain new types of polymer dispersion. 

As a method of clustering the centroid technique was used (Dixon 1983). For that set of clusters, which has six elements, the results are shown in FIGURES. It can be seen that a higher degree of chlorination leads to a more pronounced accum ulation together with some degree of volatility. The effect of chlorination is cancelled if additional polar substituents such as OH, NH2 introduced. These compounds remain in the fluid compartment. 

During PO processing at elevated temperatures, highly volatile additives may contaminate the atmosphere vapors or gases may lead to toxic effects for humans, but appropriate protection measures (local exhaust devices) can prevent this. 

The effect of the rice volatiles additive on toxic bait consumption was then evaluated (110). Two groups of rats were given a choice between either 0.2 zinc phophide treated rice and untreated rice, or 0.2% zinc phosphide treated rice with the rice volatiles added and untreated rice. This latter group showed almost double the toxic rice bait consumption and a mortality of... 

The successful application of an external standardization or the method of standard additions, depends on the analyst s ability to handle samples and standards repro-ducibly. When a procedure cannot be controlled to the extent that all samples and standards are treated equally, the accuracy and precision of the standardization may suffer. For example, if an analyte is present in a volatile solvent, its concentration will increase if some solvent is lost to evaporation. Suppose that you have a sample and a standard with identical concentrations of analyte and identical signals. If both experience the same loss of solvent their concentrations of analyte and signals will continue to be identical. In effect, we can ignore changes in concentration due to evaporation provided that the samples and standards experience an equivalent loss of solvent. If an identical standard and sample experience different losses of solvent. 

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