Biomedical Engineering Reference
In-Depth Information
operation, sample handling and how the matrix is arranged physically. These
formats have become widely recognised as useful techniques in early process
development (some of the variables examined by HTS are shown in Fig. 2 ).
Compared with larger-scale operation, feed and time savings using high-
throughput automated systems can be up to a couple of orders of magnitude. The
resulting data can then be used to home in on feasible operating ranges. Microscale
data can be used to elucidate capacity, selectivity, kinetic and thermodynamic
data, but conversion of outputs into column predictions is complicated by scale
and operating differences. Thus, the scale-down data can be used in their raw form
for approximate screening, or through theoretical or empirical models for more
accurate scale-up predictions.
4.2 General Considerations
4.2.1 Robotic Versus Manual Operation
It is possible to operate all three microlitre scale-down formats manually, although
doing so with tips or miniature columns while maintaining a consistent fluid flow
rate/contact time is prone to error. Robotic platforms can simplify sample han-
dling, accuracy and reproducibility. Such systems have multiple pumping channels
and can be specified with manipulating arms to grip microtitre plates and move
them to other equipment e.g. for agitation, solid-liquid separation or spectro-
photometry. The ultimate form of this is 'walkaway' automation, which minimises
the requirement for user intervention for routine activities.
4.2.2 Scale and Convenience Issues
The selection of matrix volume depends in part upon the type of study being
conducted; e.g. for an overloading study used to determine maximum binding
capacities, using as small a resin volume as possible will minimise the sample
volume needed for saturation. Nevertheless, there is a practical limit to how low
the feed volume can be, and it may be limited by robotic precision and accuracy.
Batch incubation filter plates are available for selected commercial matrices,
containing small pre-dispensed resin aliquots (e.g. 2-lL GE plates). Atoll GmbH
sells packed miniature columns with between 50 and 600 lL and PhyNexus sells
chromatography pipette tips with between 5 and 320 lL of matrix. In all cases,
resin volumes are available at discrete values within the specified ranges. Self-
dispensed plates can be used for any combination of resin type/volume from pre-
existing stocks, leaving the filter plate as the main consumable cost and making
this format cheaper than self-dispensed plates. Conversely, pre-dispensed plates
remove the need to aliquot matrix and offer consistent resin volumes.
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