Quadra 4 Operator Manual
Tomtec
180
Section VII - Bioanalytical Applications
1.0 Aqueous and Organic Pipetting
The features of the Quadra 4 450
µL
pipettor head has made it the dominant
instrument for BioAnalytical applications. It lives on its history of use in the
Quadra 96 Model 320 and Quadra 3. Quadra 4 platform is the third generation
design and may be supplied with stackers and automated filtration for full walk
away automation. The other option is the lower cost, non-stacker equipped,
Quadra 4 SPE Model.
When pipetting volatile organic fluids, it is necessary to first fill the tip head
space (dead air volume) with the organic vapors. Otherwise, as the organic
evaporates to equilibrate the head space, this decreases the negative
pressure (tip vacuum) that is holding the column of liquid in the tip. The result
is the tips drip.
To prevent the dripping action, first use the mix function to aspirate and
dispense 450
µL
one or more times, depending on the organic involved. A more
volatile organic such as MBTE may require 2 or 3 mix cycles. Actonitrile (ACN)
may only require 1 or 2. An expedient for less volatile liquids, such as the
alcohols, is to aspirate the desired volume followed with a 10
µL
air gap. The
organic may not have displaced the air gap before the final dispense is made.
An even more important consideration is to clear the tips of the organic vapors prior
to pipetting aqueous liquids. This is easily accomplished with the Quadra 4 by
making 2 or more time dispense functions. This opens the pinch clamp, allowing air
pressure, from the internal air tank, to clear the tips of organic vapor. If the organic
vapors are not cleared, the well condense in the head space which has the opposite
effect. The condensing vapors decrease the negative pressure in the tip head
space, aspirating a higher volume than required. This affects the accuracy of the
pipetting.
2.0 Protein Precipitation, Liquid/Liquid, And SPE
For some applications the required mixing of protein and organic may be
accomplished on the Quadra 4 eliminating the secondary operation of vortexing.
Using a deep well plate, (1mL or 2mL), mixing may be accomplished using bubbling
or injection as described before. Before aspirating free air for bubbling, make a time
dispense to clear the orifices of precipitated protein. The use of protein filter plates
(i.e. Waters Sirocco, Varian, Captiva, etc.) can eliminate the centrifuge requirement
for separation. Tomtec's automated vacuum box accessory can provide full walk-
away automation for filtration protocols.
To Next Page
Loading...