Biological separations

Reaction kinetics at phase houndaiies. Rates of adsorption and desorption in porous adsorbents are generally controlled by mass transfer within the pore network rather than by the kinetics of sorption at the surface. Exceptions are the cases of chemisorption and affinity-adsorption systems used for biological separations, where the kinetics of bond formation can be exceedingly slow. 

Mammalian Cells Unlike microbial cells, mammalian cells do not continue to reproduce forever. Cancerous cells have lost this natural timing that leads to death after a few dozen generations and continue to multiply indefinitely. Hybridoma cells from the fusion of two mammalian lymphoid cells, one cancerous and the other normal, are important for mammalian cell culture. They produce monoclonal antibodies for research, for affinity methods for biological separations, and for analyses used in the diagnosis and treatment of some diseases. However, the frequency of fusion is low. If the unfused cells are not killed, the myelomas 1 overgrow the hybrid cells. The myelomas can be isolated when there is a defect in their production of enzymes involved in nucleotide synthesis. Mammahan cells can produce the necessary enzymes and thus so can the fused cells. When the cells are placed in a medium in which the enzymes are necessaiy for survival, the myelomas will not survive. The unfused normal cells will die because of their limited life span. Thus, after a period of time, the hybridomas will be the only cells left ahve. 

Sludge Precipitated mechanically or biologically separated solid matter produced during water and or sewage treatment or industrial processes. Such solids may be amenable to biological control. 

The technologies currently available for post-combustion capture are classified into five main groups absorption, adsorption, cryogenics, membranes and biological separation. The most mature and closest to market technology and so, the representative of first generation of postcombustion options, is capture absorption from amines. 

Today their initial work on the preparation of suitable asymmetric membranes has touched nearly every aspect of life including uses in water purification, food technology, biological separations, waste treatment, medical applications, and bioengineering, and this appears to be just the beginning. 

Cross-flow filter performance is often characterized by a flux rate, which equates to the permeate flow rate per unit area of membrane surface. The flux rate in most biological separations is reduced by a fouling phenomenon called gel polarization, which tends to concentrate material at the surface of membrane to impose an additional resistance to transmembrane flow. The deterioration in flux rate must be well characterized for a commercial bioseparation process to ensure the correct size for the cross-flow filtration unit and avoid hold-ups at this processing stage. 

The incorporation of micelles in the mobile phase in capillary zone electroporesis permits the efficient separation of a variety of neutral compounds. Efficiencies in excess of 100,000 plates/m are routinely attained. The mass transport processes which are important in micellar electrokinetic capillary chromatography are described, along with the technique. The technique is particularly useful for biological separations. Preliminary data and discussion related to column selectivity and efficiency are presented. 

FIGURE 43.9 Magnetic membrane proposed for biological separation. (Reprinted from Barbie, M., J. Magn. Magn. Mater., 249, 357, 2002. With permission from Elsevier.)... 

Affinity chromatography is a form of adsorption chromatography, wherein the solid support surface has been functionalized with an immobilized compound (ligand) that complements the solute (ligate) to be separated from a complex mixture. It is an important technique for difficult biological separations. Here, it exploits the unique ability of proteins to specifically bind molecules noncovalently. 

Indeed, biological separations present some unique problems for separations engineers. It is likely ihet this will lead to concentrated efforts to develop new techniques that mey be used in place or or along with more conventions separation processes. 

The assistance furnished to or by associated treatments ranges in significance and magnitude. On occasion much benefit may be derived from a very simple auxiliary treatment e.g., many operations have been aided by pre-filtration through diatomaceous earth to remove slimes that would otherwise coat the surface of the carbon and diminish the adsorptive capacity. In contrast are the specialized and elaborate techniques employed in some biological separations. Let us briefly review types of auxiliary aid and associated procedures. 

Formation of suitable derivatives from bile acids has also been a subject of numerous studies. Since the earlier procedures have been reviewed [314-316], a continuous interest in the subject of derivatization appears to indicate that there is still a need for improvement. The initial derivatization of the acidic function to form methyl esters seems to be almost universally employed, while the remaining functional groups (hydroxy and keto) can be converted to a number of derivatives. A number of earlier and more recent studies have endorsed silylation, although various types of acylation are also common [219]. Permethylation has also been advocated recently [22S], but no biological separations were demonstrated using this approach. 

The above theoretical analysis may form the basis of future columns for the HPLC separation of proteins and other biomacromolecules. However, certain practical considei ons will probably further shape the future de n of columns for large-molecule sqKuations. For example, biological samples are often dirty, and tend to plug small-particle columns. This problem will certainly be exacerbated, if submicron particles are ever used. Biological separations are also often intended fbr recovety of hlAxihlUtll illiounts of... 

Biological Separations. As early as 1985, Cline-Love showed that the surfactant molecules contaiaed in the micellar mobile phase were able to bind to proteins and to reduce greatly their adsorption on the silica based stationary phases. The direct injection of biological samples such as serum or urine samples can be done m MLC without protein precipitation inside the column [51], This property initiated a great interest for MLC and a high number of works in this area [32, 52-55]. 

---