Quadra 4 Operator Manual
Tomtec
188
Section IX - Pipetting Recommendations
1.0 Tip# 1
When dispensing into the assay plate, set the tip height slightly above what will be the
final volume. This will prevent creating air bubbles in the well due to the air gaps. Air
bubbles may affect the readout with some plate readers. They are difficult to remove in
a 384 well plate.
2.0 Tip #2
The Dupont Dryfilm RA
coated stainless steel small volume tips are hydrophobic.
Dispense the blow out air above the final well volume. A small air bubble or droplet may
be formed on the tip. Dip the tips back into the well to wick off this droplet.
Polypropylene tips are not as hydrophobic as Dupont Dryfilm RA coated tips. When
using polypropylene tips, set the tip height for the blow out air at the top of the well. The
Quadra stage also permits touching the polypropylene tips to the well sidewall. This will
not be effective with the stiff Dupont coated tips. Not only will they not bend but the
taper at the orifice prevents it from touching the side wall.
3.0 Tip #3
When transferring 0.5µL aliquots the best Cv is obtained by using pipeline pipetting. The
other reagents in the assay are aspirated into the tips, first using air gap separation.
Aspirate the 0.5µL aliquot last, do not separate it with an air gap. Keep it in contact with
the last reagent. This utilizes surface tension between the two liquids to support the
0.5uL aliquot.
When transferring 0.5µL it is recommended that the tip exterior be rinsed in the tip
washing station. If only 50 nanoliters is on the tip exterior, it represents a 10% error over
the desired 500 nanoliters. Prior to dipping the tips, aspirate a 2-3µL air gap at the
orifice. This will prevent the surface tension of the rinse water from attracting and
diluting the 0.5µL aliquot. Tests have shown this method of pipetting small volumes will
result in a Cv of 2-3% when using the 96SV or 384 tips.
The above applies only to the Teflon
®
coated needles of the 96SV and 384 head. These
results cannot be obtained with the polypropylene tips of the 450µL head. At 10µL they
will consistently provide a Cv of 2%. At the 2-5µL level, the Cv may be expected to be
in the 3-5% range with careful pipetting techniques.
4.0 Tip #4
There are some applications that 0.5µL aliquots need to be dispensed into a dry well
without the use of washing out. Testing has shown the following:
a. Set the tip height carefully to obtain 100% touch off of all needles. If set too loose or
too tight to the late well bottom, some spots will be missed. There is about a 0.010
inch (thickness of three sheets of copy paper) variation that is allowed for 100% touch
off.
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