Purification, Concentration, Preservatives

Flame-hydrolyzed silica with specific surface areas in the range of 200-400 m g, under the name of Cab-O-SiK, i dispersible in water at pH 9 with ammonia, for example, to give sols up to 30% by weight of silica, provided the material is passed through a homogenizer to break apart the three-dimensional network of ultimate particles. The resulting particles still consist mainly of chainlike aggregates which increase the viscosity (120). 

Colloid milling of pyrogenic silica in water in the presence of boric acid or alkali borate is disclosed by Clapsdale and Syracuse (122). A 30% sol can be prepared. Some additional patents on making sols from pyrogenic silica mainly involve the use of alkali stabilization with sodium silicate, sodium hydroxide, hydrazine, hydroxylamine, or mixtures with pyrogenic metal oxides (123-125). 

Sols made by some processes contain salts or other materials that must be reduced or removed before the sol is finally concentrated. 

Special purification procedures to remove salts from the final concentrated sols usually involve treatment with ion-exchange resins to remove soluble salts and then stabilization with a minimum of base, including ammonia, to obtain a sol of 

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In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

HSA is used therapeutically as an aqueous solution it is available in concentrated form (15-25 per cent protein) or as an isotonic solution (4-5 per cent protein). In both cases, in excess of 95 per cent of the protein present is albumin. It can be prepared by fractionation from normal plasma or serum, or purified from placentas. The source material must first be screened for the presence of indicator pathogens. After purification, a suitable stabilizer (often sodium caprylate) is added, but no preservative. The solution is then sterilized by filtration and aseptically filled into final sterile containers. The relative heat stability of HSA allows a measure of subsequent heat treatment, which further reduces the risk of accidental transmission of viable pathogens (particularly viruses). This treatment normally entails heating the product to 60 °C for 10 h. It is then normally incubated at 30-32 °C for a further 14 days and subsequently examined for any signs of microbial growth. 

As regards extracts, their composition varies greatly according both to the methods of preparation and purification and to the degree of concentration. With these the possibility of adulteration, especially with glucose, molasses, cellulose extracts and mineral salts, is to be considered. Addition of sulphurous anhydride or sulphites is allowed, for either clarification or preservation of the extract the proportion of total sulphurous acid may reach and even exceed 2%. 

Hydrochloric and nitric acids have been used as preservatives for urine specimens for metal analyses, and mineral acids are extensively used in graphite furnace analysis of trace elements in biological specimens (e.g. Gills et al., 1974 Stoeppler and Brandt, 1980). Historically, concentrations of trace elements in commercially available acids have been incompatible with analysis of trace elements in biological samples (Kuehner et al., 1972). However, present commercial ultra pure hydrochloric, nitric, sulphuric and perchloric acids have been reported to be suitable for trace element analysis in urine without further purification (Golimowski et al., 1979 Brown et al., 1981 Veillon et al., 1982). 

In all other cases, when the biological activity has to be preserved, the environmental conditions for purification are very limited, usually requiring room temperature or below, salt concentrations in the range of an osmotic pressure around 400Mosmol, and a pH close to 7.0. In cases where these conditions cannot be maintained, the protein should be kept in its unfriendly environment as briefly as possible. Usually small peptides are much more stable than proteins, and they can be dissolved in organic solvents and withstand harsh conditions. 

In Chapters 13 and 14 of this book the applications of conventional chemical catalysts were described. The use of enzymes or whole cells as catalysts for chemical transformations is well known. They can bring about various reactions at ambient temperature and pressure and afford high reaction velocities. In fact, enzymatic reaction sequences may be designed to give the ideal efficiency embodied in the second law of thermodynamics. Thus, hundreds of compounds that are very difficult to prepare by purely chemical methods may be obtained quite readily and economically with the help of enzymes. Until recently, most laboratory investigations and manufacturing processes employed soluble enzymes in dilute aqueous solutions. Before use, the required enzyme must be obtained from biological sources as a concentrated extract. It is not uncommon for a particular type of cell to contain many proteins in addition to the one desired. Therefore, the purification and concentration of enzymes in preparation for use is a very cumbersome process. When used in solution, enzyme catalysts are invariably lost after each batch operation. The use of immobilized enzymes and whole cells has been proposed as a means that could eliminate such losses and preserve hard won stocks of specialized enzymes. 

The purification of waste water from phenol compounds is one of the most essential tasks of green chemistry considering the hazardousness of phenols. Although numerous methods are known for the elimination of phenols from water, the majority of them are physical methods that preserve the phenol mass balance, i.e., lead to the pollutant redistribution/concentration without its transformation to non-hazardous substances. The ideal purification is a complete oxidation of phenols to CO2 and H2O. Catalytic conversion is considered to be the best solution to this problem. 

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