Physical Techniques Used in Purification

Purification processes require several steps in order to obtain a commercially pure product. Affinity chromatography is therefore extremely useful, but until a few years ago, was limited to antibodies produced by the immune systems of laboratory animals. However, antibodies often cannot discriminate between closely related impurities. In addition, the drastic sanitation conditions used in the production of therapeutic products may denature the antibodies. Phage display technology allows the isolation of affinity ligands with the required physical and chemical properties. This technique can also discriminate between the target and closely related impurities. Small peptides bound to resins are well suited for use in purification of proteins that are normally used as drugs. Once a peptide with... 

The small synthetic scale used for production of many labeled compounds creates special challenges for product purification. Eirst, because of the need for use of micro or semimicro synthetic procedures, the yield of many labeled products such as high specific activity tritiated compounds is often low. In addition, under such conditions, side reactions can generate the buildup of impurities, many of which have chemical and physical properties similar to the product of interest. Also, losses are often encountered in simply handling the small amounts of materials in a synthetic mixture. As a consequence of these considerations, along with the variety of tracer chemicals of interest, numerous separation techniques are used in purifying labeled compounds. 

Adsorption in water treatment is a robust technique for removing water-soluble ions, especially when these ions exist in water at low concentrations. Coincidentally, fluoride ions exist in some groundwaters at low concentrations, which are above the permissible limits. The principle behind this technique is that a component (fluoride in our case) is transported by diffusion from the bulk phase to the solid surface where it is bound at the surface or interface between two phases by either chemical or physical forces [35], Numerous investigations have focused on surface adsorption as a means of removing fluoride from water. As a result of these studies various water treatment plants using treatment media such as activated alumina or bone char have been constructed and are in use in several countries. One example is a water purification plant in Kansas that utilizes activated alumina [36], Several other smaller fluoride treatment facilities are scattered all over India, Kenya and Tanzania, among other nations. 

Physical Methods and Physical Chemistry.—Physical diet hods, e.g. chromatographic and spectroscopic techniques, are used routinely in the separation, purification, and characterization of carotenoids and related compounds, and of intermediates in their synthesis. This section will consider only those papers which are devoted largely or entirely to detailed study or analysis of such physical techniques, or which include systematic surveys, often with tabulated data. 

The adsorption process involves the reversible physical or chemical fixation of vapor or liquid to a porous solid. These processes are caused by van der Waals forces or electrostatic interactions. Generally, adsorption is used either for purification where the product has little value, as a separation technique as in chromatography [189-191], or as a collection technique if the product has sufficient value [194—198]. When the product is to be collected, such techniques as temperature swing adsorption (TSA), pressure swing adsorption (PSA), or displacement are commonly used. Ion exchange has also been included in this section as it has many parallel uses and can be considered as chemical adsorption [192, 193]. 

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