Biomedical Engineering Reference
In-Depth Information
system), which can result in differences in gradient shape, which will further impact the
process (Fig. 13.6b). Again, if the process is defined in the appropriate terms, it should be
simple to justify modifications to operating conditions to ensure that the correct
combination of process parameters, corresponding to the design space for that step,
is delivered, see Fig. 13.6c.
During operation the system should be monitored for continued fitness of purpose.
Packing integritymay fail with time, this can bemitigated by tracking performance using
transition analysis of internal markers, which has been shown to be a useful predictor of
potential failure [36]. As additional experience is gained with the separation, PAT tools
can be used to fine tune performance, for example by modifying the steepness of the
gradient or varying flow rates to shorten elution times, improve yields, increase loading,
improve quality, or decrease buffer consumption, provided of course that attention is paid
both to the behavior of the product of interest and the impurities and contaminants such
that quality is not compromised. Again, this is a science- and risk-based assessment
based on an understanding of differences in properties between the different molecules
(e.g., pI and titration curves in the case of an ion exchange separation).
Figure
13.6.
A variability introduced by materials and equipment. (a) Variation in retention
time and pool volume resulting from differences in buffer conductivity. The three runs show
differences based on the source. Reproduced with permission from Ref. [35]. (b) Variation in
gradient shape arising from differences in equipment scale and design. The runs show differ-
ences in slope and linearity between two different systems, A and B. Note the change in linearity
for systemBafter 1500 S. Unpublisheddata fromAmgen. (c) Variation in retention timeandpeak
shape caused by differences in gradient shape. Steeper gradients result in shorter elution times
and sharper peaks. Unpublished data from Amgen.
