TomTec QUADRA 4 - Page 83

Quadra 4 Operator Manual
Tomtec
83
TARGET(SOURCE)
The "Target" volume. height, speed, etc. Set the "Source" plate volume. The operation
will pre-wet the tips, aspirate the default tip volume, and then dispense the delta to
achieve the target volume.
TARGET(DESTINATION)
The "Dispense" height, speed, timed dispense height, etc. Set the Destination" plate.
Generally all but 3ul is dispensed at the destination plate. The remainder is dispatched
by a timed dispense function. If the volume is less than 3ul, the dispense is skipped,
and the timed dispense will be done.
NOTES: TARGET METHOD PIPETTING
The target method takes advantage of the fact that higher positive pressures
may be developed within the tip on a dispense motion, compared to the low
negative pressures that are available for aspiration. The target method is only available
for pipetting volumes less than 50µL. If target method is selected on the source
characteristics of any template, it will automatically aspirate and dispense 30µL, first
to pre-wet the tip. Then it will aspirate a 50µL volume and automatically
dispense back to the target volume to be dispensed. For example, assume 10µL is
the desired target volume. 50µL is aspirated and 40µL is automatically dispensed back
to the source with the tip submerged in the source liquid.
If target injection is selected for the destination characteristics, then the following action
will occur if the delivery volume is less than 50µL. The dispense will automatically be
made at the top of the well (as determined by the database for the plate selected in the
deck layout. You must use the correct plate layout). All but 3µL of the tip volume will be
dispensed by piston displacement.
The final 3µL will be blown out using the time dispense function. The air pressure for the
time dispense function should be set at 3 psi.
The 3µL blow out volume was derived empirically. At 8µL, the fluid flow was not
fast enough to overcome the surface tension forces at the orifice and the dispensed
liquid may form a drop on the tip exterior. The small 3µL volume and 3 psi driving force,
accelerates the liquid fast enough to minimize or eliminate the clinging drops on the tip
exterior.