Adsorption processes chromatography

Downham, M., Busby, S., Jefferis, R., and Lyddiatt, A., Immunoaffinity chromatography in biorecovery an application of recombinant DNA technology to generic adsorption processes, /. Chromatogr., 584, 59, 1992. 

Storti, G., Masi, M., Morbidelli, M. (1993) Modeling of countercurrent adsorption processes. Preparative and production scale chromatography. In Chromatographic Science Series, Vol. 61. Eds. Ganetos, G., Barker, P.E. Marcel Dekker, New York, 673-700. 

Because of the different interactions involved in partition and adsorption processes, they may be applied to different separation problems. Partition processes are the most effective for the separation of small molecules, especially those in homologous series. Partition chromatography has been widely used for the separation and identification of amino acids, carbohydrates, and fatty acids. Adsorption techniques, represented by ion-exchange chromatography, are most effective when applied to the separation of macromolecules including proteins and nucleic acids. 

Apart from partition and adsorption processes, chromatographic separations may also be based upon differences in molecular size (gel permeation chromatography, or gel filtration). In this technique gel-like material, which is commercially available in a range of porosities, serves as the stationary phase, and separation is achieved through differential diffusion into the pores of the matrix, of molecules which are not large enough to be completely excluded. 

Saccharification produces a 94% dextrose liquor, which can be processed in several ways. To make a dextrose syrup, the fats and protein are removed from this liquor, as in the high fructose process. The syrup is then carbon bleached, demineralized and evaporated to 71% solids. The 94% dextrose liquid may also be further refined to 99% dextrose by adsorption-separation chromatography prior to being bleached, demineralized and evaporated. 

Microscopic Kinetic Description of the Adsorption Process in Gas Chromatography - Monte Carlo Methods... 

Lyddiatt, A., Process chromatography Current constraints and future options for the adsorptive recovery of bioproducts, Curr Opin Biotechnol. 2002 (2) 95 103. 

The system of differential equations is too complex to be solved analytically. Assumptions of a linear adsorption isotherm can be used to obtain analytical solutions, but this approach is generally not applicable to describe affinity chromatography experiments. Several numerical techniques arc used to solve the system of partial differential equations. The other method is to use an analytical solution with simplifying approaches [32] that describe the adsorption process with a single step and a lumped mass transfer coefficient [27],... 

Gas chromatography may be divided into gas solid chromatography (mainly adsorptive processes) and gas-liquid chromatography (mainly partition) depending on whether the stationary phase is a solid or a liquid at its operating temperature. If the stationary phase is a hquid it must be coated on a support for packed coliunn chromatography. For capillary column chromatography, the stationary phase may be coated directly on to the walls of the coliunn, or on to a support which is bonded to the... 

Reiger and Ballschmiter [43] described a multistep method for PCA analysis in sewage sludge by cyclohexane-isopropanol extraction and cleanup on silica gel column chromatography. Fractionation on silica gel was achieved by eluting with hexane (FI), which desorbed hexachlorobenzene, 4,4 -DDE, PCB, PCDD, and PCDF. PCAs were then desorbed from the column with (90 10) hexane/di-ethyl ether. The recovery of PCAs by this method was 86%. These authors also noted that cleanup chromatography on activated alumina should be avoided because PCAs were either totally or partially destroyed by dehydrochlorination during the adsorption process. 

To obtain individual phospholipids of greater than 50-60% purity, some form of selective adsorption process is usually required. Adsorption and distribution chromatography present these options. Treatment of the alcohol-soluble lecithin with alumina yields a fraction very rich in phosphatidylcholine and free of phosphatidylethanolamine and phosphatidylinositol (167). Although these products are available only in very limited quantities for highly specialized markets, products such as a lecithin containing up to 95% PC can be obtained commercially. 

A dual-solvent fractional extraction process can provide a powerful separation scheme, as indicated by the examples given above, and some authors suggest that fractional extraction is not utilized as much as it could be. In many cases, instead of using full fractional extraction, standard extraction is used to recover solute from a crude feed and if the solvent-to-feed ratio is less than 1.0, concentrate the solute in a smaller solutebearing stream. Another operation such as crystallization, adsorption, or process chromatography is then used downstream for solute purification. Perhaps fractional extraction schemes should be evaluated more often as an alternative processing scheme that may have advantages. 

Adsorption or chromatography is one of the best known methods of approach to the problem of isolating an active principle. Once a suitable adsorbent has been found, the problem is not difficult. The approach used for countercurrent distribution can aid in understanding the process (solid phase which takes the place of the heavier phase in the series of separatory funnels. If an adsorbent and solvent is chosen so that about half the solute is adsorbed from the solution, the conditions are met for easy application... 

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