Biomedical Engineering Reference
In-Depth Information
4.5.2 Types of Miniature Columns
Centrifuge Columns
There are three types of miniature column supplied by Atoll. The first is operated
centrifugally, with a reservoir located above the resin bed and through which
buffers or feed solutions can be spun. The size of the reservoir varies according to
the resin bed volume underneath; e.g. the 50-lL bed has a 315-lL reservoir,
whereas the 200-lL bed has a 230-lL reservoir. Such columns are best employed
where there are many samples available for processing but where robotic platforms
are unavailable. Liquids are driven through at between a few hundred and a few
thousand rpm (with recommended values of 1,000 rpm for 60 s, although the
impact of this upon residence time needs to be borne in mind). Centrifuge columns
enable very fast initial screening. It is important to check that the centrifuge bowl
in question can accommodate the full height and footprint of the column stack.
Pipette Columns
The second column type relies upon manual or motorised handheld pipetting to
pass liquid through a bed using a standard pipette tip and an adaptor at the top of
the column which forms a seal around the tip. The recommended dispense rate is
around 0.5 mL/min. This format is useful when one needs to regulate liquid flow
through the bed but where automated workstations are unavailable and again are
useful for early-stage resin screening. 'Starter kits' are also available, being
designed for simultaneous screening of eight different resins in pipette-compliant
miniature columns.
Robotic columns
The third column type is controlled robotically, with an inlet adaptor enabling a
reversible seal to be formed with fixed tips to introduce buffers or feed. The
column inlet possesses a conical duct which enables the fixed tip to be directed
into the column inlet, where an O-ring ensures a tight seal. A frit is located at the
top of the bed. The volume of liquid that can be delivered in one go is limited by
the pipetting capacity of each liquid handling channel, and where the total volume
exceeds the channel capacity, several cycles are used. Fractionation in microtitre
plates can be achieved by automation, with devices used to position a plate
underneath the column stack to collect liquid droplets.
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