Membrane adsorbers

Bedzyk and co-workers used the XSW technique to probe the ion distribution in the electrolyte above a charged cross-linked phospholipid membrane adsorbed onto a silicon-tungsten layered synthetic microstructure (LSM) as shown in Figure 2.80(a). The grazing-angle incidence experimental set-up... 

Membrane absorbers are continuous chromatographic supports, which circumvent some of the above-mentioned problems of particulate stationary phases. They were originally derived from membrane (filtration) technology. The immobilization of interactive (ionic, hydrophobic, or biospecific) groups on the surface of microfiltration membranes was found to increase the selectivity of certain separation procedure. Ideally such activated membranes, or membrane adsorbers, allow the selective adsorption of certain substances and substance classes, which may subsequently be eluted by means of a stepwise change of the mobile phase (elution buffer). More complete information on the various types of modern membrane technology can be found in some recent reviews [e.g., 31-33]. 

The most important feature of monolithic media is that the mobile phase flows exclusively through the separation unit. In contrast, there is no flow inside the conventional porous chromatographic particles and only a partial flow through the perfusion beads. Just as with the membrane adsorbers, monolith stationary phases may be operated with a minimum in mass transfer resistance with the concomitant advantages in terms of speed and throughput. 

Reif, O.W, and R. Ereitag, Comparison of membrane adsorber (MA) based purification schemes for the down-stream processing of recombinant h-AT III. Bioseparation, 1994. 4(6) 369-81. 

Fig. 10 Schematic of headspace sampling by a HWG internally coated with an extractive polymer membrane adsorbing the analytes investigated [47]...

In addition, it has been shown that membrane adsorbers are competitive in bind-and-elute applications for large solutes such as DNA, RNA, and viruses. Most bead chromatographic media have pore sizes that are too small, which exclude large molecules from entering and binding to specific sites. Under these circumstances, membrane chromatography exhibits a competitive binding capacity for these molecules, such as DNA. 

Membrane adsorbers derive from the technological developments in the membrane separation field and in column chromatography of proteins. They combine the high selectivity of chromatographic separations and the high productivity usually obtained in membrane separation processes. 

The use of microporous membranes as a chromatography matrix avoids intraparticle diffusional limitations, since their pores, around two orders of magnitude larger than those of conventional resins, are accessed mainly by convection (Figure 12.10). This enables the operation at relatively high flow rates, with relatively low pressure drops. Additionally, membrane adsorbers present better mechanical resistance than gels, with no deformation and bed compaction problems. Also, the systems are usually modular and easy to scale up (Klein, 2000 Bueno and Miranda, 2005). 

Comparison of solute transport to the adsorption sites (A) in conventional porous resins and (B) in membrane adsorbers. Adapted from Ghosh (2002). 

TABLE I Summary of Commercially Available Membrane Adsorbers... 

FIGURE 2 Photo of stack of flat sheet disk membrane adsorbers in a filter holder. (Courtesy of Sartorius Corp.)... 

FIGURE 8 Arrangement of multiple radial flow modules to increase capacity and flow rate. Two 8 m2 modules were connected in parallel, with one 4 m2 module in series, in conjunction with a final I m2 module in series. Total membrane area is 21 m2. (Adapted from Journal of Chromatography, Vol. 852, W. Demmer and D. Nussbaumer, Large-scale membrane adsorbers, 73-81. Copyright 1999 with... 

Freitag, R., Splitt, H., and Reif, O.-W. (1996). Controlled mixed-mode interaction chromatography on membrane adsorbers. ]. Chromatogr. A 728, 129-137. 

Chaudhary, A., Mehrotra, B., and Prestwich, G. D. (1997). Rapid purification of reporter group-tagged inositol hexakisphosphate on ion-exchange membrane adsorbers. BioTech-niques 23, 427-430. 

Ruth, M. E. (1996). Use of a Q-type membrane adsorber for the removal of DNA during the purification of a monoclonal antibody. PrepTech Con/., East Rutherford, NJ, 1996. 

Levine, H. (1995). The use of membrane adsorbers for the purification of monoclonal antibodies. BioWest 95. 

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