TomTec QUADRA 4 - Section VI: Pipetting with the Positive Displacement Pipettor Head; Pipetting 0.5µl with Positive Displacement; Dispensing 0.5µl spots - Aqueous

Quadra 4 Operator Manual
Tomtec
178
Section VI - Pipetting with the Positive Displacement
Pipettor Head
The 96 SV, 96 LV, 384 SV, and 384 LV pipettor heads are all positive
displacement designs. The 60 µL SV heads were designed to aspirate and
dispense small volumes down to 0.5 µL . They use a swaged tip orifice. The
200 µL LV pipettors are designed for higher volumes (200 µL ) with some
sacrifice at the 1 µL level.
The positive displacement designs, do not have the tip blow through feature
of the air displacement design. To clear the tip orifice of residual, they use
piston derived blow out air and surface contact touch off. The dip tip function
after a dispense is also very useful.
The SV heads are capable of aspirating and dispensing 0.5uL volumes with a
CV of 2-3% providing careful pipetting techniques are used. These are
detailed as follows. They are primarily based on transferring 0.5 µL of
compounds in 100% DMSO into a 25-50 µL assay.
1.0 Pipetting 0.5µl with Positive Displacement
When transferring 0.5 µL 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 0.5 µL 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 0.5 µL aliquot.
When transferring 0.5 µL it is recommended that the tip exterior be rinsed in
the tip washing station. If only 50 nanoliters is on the tips exterior, it
represents a 10% error over the desired 500 nanoliters. Before dipping the
tips, aspirate a 2-3 µL air gap at the orifice. This will prevent the surface
tension of the rinse water from attracting and diluting the 0.5 µL aliquot. Tests
have shown this method of pipetting small volumes will result in a CV of 2-3%
when using the 96SV or 384 SV tips.
The above applies to only the Teflon coated needles of the 96SV and 384SV
head. These results cannot be obtained with the polypropylene tips of the
450uL head. At 10 µL they will consistently provide a CV of 2%. At the 2-5 µL
level, the CV may be expected to be in the 3-5% range with careful pipetting
techniques.
2.0 Dispensing 0.5µl spots - Aqueous
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
when pipetting aqueous solutions.