Extraction surface-active contaminants

Reductions in mass transfer rates due to the piesmice of trace amounts at surfece-acdve contaminants may be substantial. These effiects have been measured for each of the two phases during drop formation, free fall, and coalescence and, although correlation was not achieved, at least those existing relationships that came closest to the data in each case were identified. These observations were systematized by Skelland and Chadha, who also develc ied criteria for selection of the disperse phase in spray and plate extraction columns both in the presence and the absence of surface-active contamination. 

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

The longer a freshly machined wood is exposed to the atmosphere, the more inactivated it becomes. To prevent surface inactivation in wood two measures should be taken. First, the wood must be dried with care taken not to overdry or overheat the wood. Second, the wood should preferably be planed before bonding to remove hydrophobic and chemically active extractives and other contaminants that could interfere with bonding. 

When the aim is isolation for identification by direct probe insertion mass spectrometry (MS), plastic materials, filter papers, and blenders should be avoided to prevent contamination during extraction and chromatography. It is also very important to avoid the cis-trans isomerization of carotenoids in solution, which is accelerated by heat, light, acids, and active surfaces. Therefore, a pure carotenoid or even a crude extract should never be stored in solution it should be kept completely dry in an inert atmosphere at low temperature. 

PT catalysts are often difficult to separate from the product, while it is also desirable that the catalyst should be reusable or recyclable. Distillation and extraction are the most common separation processes. The main disadvantage of lipophilic quats is their tendency to remain in the organic phase and consequently contaminate the product. Therefore, extraction in water often is not satisfactory. Furthermore, products in the fine chemicals industry often have high boiling points and/or are heat sensitive, which makes separation of the catalyst by distillation impossible. Often the only means to remove the catalyst in these cases is to adsorb it using a high surface area sorbent such as silica, Florisil or active carbon (Sasson, 1997). After filtration, the catalyst can then be recovered by elution. 

Extractable matter should be removed by extraction with organic solvents, e.g., xylene. This is especially important for carbon blacks (25), Oxidized carbon may contain small amounts of oxalic acid. King (33, 34) found 0.002 meq/gm of oxalic acid in oxygen-treated sugar charcoal. More severe is the contamination of the surface with adsorbed gases, mainly carbon dioxide and water. Activated carbon with narrow pores may contain considerable amounts of carbon dioxide (28). The best... 

Depending on the depth of the soil being remediated, a vacuum extraction system may be connected to vertical or horizontal extraction wells. As air flows through the soil pore spaces, the contaminants are volatilized in place and driven toward the extraction wells. Contaminants are then recovered and treated at the surface, usually by activated carbon, catalytic oxidation, or thermal treatment. 

Cmde enzyme extracts are often unsuitable for therapeutic uses because of their antigenicity, contamination with endotoxins, and rapid inactivation under physiological conditions or in fluids intended for intravenous infusion over several hours. When the enzyme used is a foreign protein, it can eHcit an immune response that alters the clearance rate or induces severe allergic reactions in the host. After an intravenous injection of an enzyme, its activity in plasma decreases with time due to distribution to other fluids and tissues, and as a consequence of proteolysis or excretion. Distribution is related to molecular size, charge, and HpophiHcity surface charges attributable to the availability of free amino, amido, or carboxyl groups may affect the rate of inactivation of some enzymes. 

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