Scaling up with
radial flow columns is a simple matter, whether you are scaling up from a
smaller radial flow column or from a conventional column.
Radial flow columns are recommended for ion exchange, affinity,
hydrophobic, reverse phase and other types of adsorption-desorption
separations.* The sample is bound to the column with one
buffer and eluted under different buffer conditions. With this type of
separation, the most critical parameter is residence time, or the time in
which the sample is in contact with the packing material. This can also be
thought of in terms of column volumes of flow per unit time.**
Scaling up, from a small radial flow column to a larger one is linear. For
example suppose you are currently running 3.5 mL sample on a 50 mL column
at 5 mL/min. To scale up 400 X, simply multiply the column volume, sample
size, and flow rate by 400. Therefore, a 1.4 L sample run on a 20 L column
at 2 L/min will give the same separation.
To scale up from
a conventional column to a radial flow column, first calculate the flow
rate in terms of column volumes per minute. For example, a flow rate of 25
mL/min through a 100 mL column is equal to 0.25 column volumes per minute.
To scale up from 1 L column, the appropriate flow rate would remain a 0.25
column volumes per minute, or 250 mL per minute. Similarly, sample size
should be thought of in terms of percentage of column volume.
Since the bed depth of radial flow columns increases from 3.5 cm on the
small columns to 10 cm on the large columns, a 3-fold pressure increase
can result. Process development on the small columns should be done at
pressures under 8 psi. This will result in operating pressures below 25
psi on a large scale.
*Isocratic
separations that are dependent upon the length of column, such as size
exclusion chromatography, are not recommended with radial flow columns.
**Because the design of radial flow columns is
significantly different from conventional columns, the use of "linear
velocity" (cm/hr) is not appropriate for calculating scale up
parameters from Superflo® Columns.
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