Page 261 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioTechnology

P1: GLQ/GLE P2: GPB Final Pages
Encyclopedia of Physical Science and Technology EN014J-683 July 30, 2001 20:3

Separation and Purification of Biochemicals 669

the medium, which can contain particles or cells, in or- are typically very low and the system can be operated
der to bind the target molecule in a one-step adsorption at very high flow rates, which may be as high as one or
process. The beads have then to be separated from the two column volumes per minute. Several applications in
medium by gravity or by applying a magnetic field in the biotechnological field have been reported even at very
the case of magnetic bead cores, or by filtration. Desorp- early stages of the purification process. Another advantage
tion and collection of the target molecule is done with of this type of column is that they are quite easy to pack
the same eluents as in chromatography. Equal recovery homogeneously.
might require slightly higher affinity constants for a sin-
gle contact in suspension vs multiple contacts occurring
3. Preparative-Continuous Annular
in biochromatography.
Chromatography
The concept of the continuous annular chromatography
2. Radial Chromatography
(CAC) was introduced by Martin in 1949. The packed bed
In radial flow chromatography, the adsorbent is packed of the adsorbent occupies the annular space between two
between two concentric cylindrical porous frits. Eluent coaxial cylinders. The bed rotates past a fixed port through
and feed flow via capillary channels from the top of the which sample is continuously fed. The eluent percolates
instrument to the outer cylinders through the stationary downward through the bed. Substances elute as helical
phase to the inner porous cylinder and then to the exit port bands due to the simultaneous axial chromatographic pro-
of the column, see Fig. 12. The separation path length is cess and bed rotation as shown in Fig. 13. The stronger
therefore comparatively short, i.e., equal to the thickness the adsorption of a given substance is, the further away
of the annulus. Radial chromatography has been devel-
oped to overcome backpressure problems that can arise
when a process is scaled up from the laboratory to the
production scale. A unit is easily scalable because the
length of the cylinder may be increased while the sample
path/backpressure stays constant. Column backpressures

FIGURE 13 Continuous annular chromatograph. [From Freitag,
FIGURE 12 Schematic representation of a radial flow column. R. and Giovannini, R. (2001). Biotechnology and Bioengineer-
[From Bioseparation and Bioprocessing: A Handbook (1998). ing, Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc. With
Vol. 1, p. 147. Wiley-VCH Verlag, Weinheim. With permission.] permission.]