Ultra-filtration method

W6. Wang, Y. S., Pekary, A. E England, M. L., and Hershman, J. M., Comparison of a new ultra-filtration method for serum free T4 and free T, with two RIA kits in eight groups of patients. J. Endocrinol. Invest. 8,495-500 (1985). 

Since membrane filtration methods such as ultra filtration or nanofiltration can discriminate according to the size of a given molecule, they can easily be used to retain biocatalysts (which are macromolecules). For chemical catalysts additional procedures have to be applied mostly. Immobilization on a solid support is used... 

The first method is more perspective, as stabilizers may inhibit destruction reaction may directly influence the mechanism of destruction with the purpose of decreasing undesirable products yield and so on. It is supposed that stabilizers may act by means of 1) blocking of active centres (weak bonds) 2) filtration of ultra-violet radiation 3) breaking of peroxides 4) interaction with free radicals 5) suppression of excited states. 

Initial investment is four times higher than the ultra-filtration method. 

Biocatalysts are not always immobilized on membranes in bioreactors, though. As enzymes are macromolecules and often differ greatly in size from reactants they can be separated by size exclusion membrane filtration with ultra- or nano-filtration. This is used on an industrial scale in one type of enzyme membrane reactor for the production of enantiopure amino acids by kinetic racemic resolution of chemically derived racemic amino acids. The most prominent example is the production of L-methionine on a scale of 400 t/y (Liese et al, 2006). The advantage of this method over immobilization of the catalyst is that the enzymes are not altered in activity or selectivity as they remain solubilized. This principle can be applied to all macromolecular catalysts which can be separated from the other reactants by means of filtration. So far, only enzymes have been used to a significant extent. 

Separation methods based on size include size exclusion chromatography, ultra-filtration, and ultracentrifugation (see Chapter Appendix). The ionic properties of peptides and proteins are determined principally by their complement of amino acid side chains. Furthermore, the ionization of these groups is pH-dependent. 

Intensive technologies are derived from the processes used for the treatment of potable water. Chemical methods include chlorination, peracetic acid, ozonation. Ultra-violet irradiation is becoming a popular photo-biochemical process. Membrane filtration processes, particularly the combination microfiltration/ultrafiltra-tion are rapidly developing (Fig. 3). Membrane bioreactors, a relatively new technology, look very promising as they combine the oxidation of the organic matter with microbial decontamination. Each intensive technique is used alone or in combination with another intensive technique or an extensive one. Extensive... 

Extraction of Sodium Channel Blockers. A review of published reports shows that methods for purification of sodium channel blockers from bacterial cultures are similar to techniques for isolation of TTX and STX from pufferfish and dinoflagellates (30, 31, 38, 39). Typically, cell pellets of bacterial cultures are extracted with hot 0.1% acetic acid, the resulting supernatant ultra-filtered, lyo-philized, and reconstituted in a minimal volume of 0.1% acetic acid. Culture media can also be extracted for TTX by a similar procedure (Ji). Both cell and supernatant extracts are analyzed further by gel filtration chromatography and other biological, chemical, and immunological methods. Few reports describe purification schemes that include extraction of control samples of bacteriological media (e.g., broths and agars) which may be derived from marine plant and animal tissues. 

A number of potential methods for homogeneous catalyst separation and recovery have been discussed in the preceding chapters. This chapter addresses the separation of homogeneous catalysts by means of advanced filtration techniques. Separation of homogeneous catalysts by size exclusion (ultra- or nanofiltration, defined in detail in Section 4.3.1) offers several advantages ... 

In terms of optimizing system performance, the flux for both cells and lysate suspensions seem to be most strongly influenced by the average trans membrane pressure, although maintaining a minimum circulation flow is critical also. Flux rates on microporous membranes for lysates are typically less than for whole cell suspensions as would be expected because of the dispersed cell debris present. Filtrates from lysate processing are typically clear, but do depend on the membrane used and the method of lysing the cells. The ultra-... 

Achieving low particulate levels in the final drug or parenteral solution usually requires filtration of the constituent water. The United StatesPharmacopoea defines specifications and methods for production of water for injection. Ultra-pure water systems in the pharmaceutical industry use reverse osmosis, ion exchange, and MF just as in the electronics industry (see below). Both industries seek to produce sterile/particle free water. However, in the pharmaceutical in-... 

Another standard method is to use a (high-speed) centrifuge to sediment the eolloids, replace the supernatant and redisperse the partieles. Provided the particles are well stabilized in the solvent, this allows for a rigorous purification. Larger objeets, sueh as particle aggregates, ean be fraetionated off beeause they settle first. A third method is (ultra)filtration, whereby larger impurities can be retained, partieularly using membrane filters with aceurately defined pore sizes. 

Directions for the storing of columns, the preservation and elution of preservatives and the methods of regeneration should also be given in procedures. Procedures used for clarification and sterile, dia- or ultra-filtration should also be available. 

Gjessing, E.T., 1973. Gel and ultra-membrane filtration of aquatic humus a comparison of two methods. Schw. Z. Hydrol. 35 286—294. 

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