Quadra 4 Operator Manual
Tomtec
179
a. Set the tip height carefully to obtain 100% touch off of all needles. If set
too loose or too tight to the plate 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.
b. Using 2
µL
of blow out air will improve the CV of the spot.
c. Dispense the 0.5
µL aliquot with the tips in free air above the wells. Then move
the tips down to the touch off height and dispense 2 µL of blow out air.
d. Do not try to rinse the tip exterior as described before. If the 0.5
µL
is not
moved away from the orifice, it will be lost without the supporting liquid
above. If rinsed with the 0.5
µL
at the orifice the rinse water will capture it.
3.0 Dispensing 0.5µl spots – DMSO
DMSO (Dimethyl Sulfoxide) is not as hydrophobic to Teflon as water is. When
aspirating DMSO, small droplets may cling to the tip exterior. On the dispense,
if the aliquot touches the tip exterior that is wetted by a droplet, the small
aliquot will follow the wetted surface up the tip exterior. Corrective action is as
follows.
a. Use the slow withdrawal function in the program when aspirating DMSO
from the source. The slow withdrawal of the tips from the DMSO allows
surface tension to clear the tip exterior of clinging droplets.
b Make the dispense when in firm contact with the bottom of the plate. The
tips should press firmly to the well bottom (just short of stage height error). Do
not dispense the drop in mid air as with aqueous.
c Keep the tips clean.
4.0 Protocol Verification
a.
Having completed a pipetting protocol, it is prudent to evaluate it, with food
coloring to represent the various reagents. This will provide a visual image of
the protocol. Look for the following criteria:l
b. Is the liquid level uniform within the tips at the end of an aspirate or dispense
function?
c. On a mix function, is liquid level following the piston motion? If not, slow the
aspirate/dispense speeds.
d. Are the tips being cleared on a dispense?
e. Is there liquid clinging to the tip exterior?
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