TomTec QUADRA 4 - Section V: Suggested Pipetting Methods and Recommendations; Aspirating Techniques; Pipeline Pipetting

Quadra 4 Operator Manual
Tomtec
175
Section V - Suggested Pipetting Methods &
Recommendations
1.0 Aspirating
The stepper motor driving the pistons has several speeds. Speed 3 is the fastest
and is recommended for aqueous pipetting, with near water like viscosity. For more
viscous liquids, use speed 2 or 1, which is the lowest. At speed 1, the stepper motor
noise increases due to the lower step rate.
If the pistons move too fast, the liquid may not follow that motion, due to the viscosity.
This can create errors in accuracy and precision. If in doubt, watch the liquid level in the
tip, follow the piston motion.
Normally, aspirations are made near the bottom of the container. These values are set
in the Quadra 4 Database. When setting these values, do not pin the tip to the bottom of
the well.
The software provides for "slow withdrawal". The speed with which the tip leaves the
liquid has an effect on drops that can cling to the tip exterior. These drops are
uncontrolled and can affect accuracy. If "slow withdrawal" is checked, the stage will
move down slowly, allowing the surface tension of the reservoir liquid, to wipe the tip
exterior. The stage moves down slowly to the clear height set in the database, for the plate
or reservoir in use. If it moves slowly all of the way, the database is being used. For
aspirating small volumes, accuracy is improved by pre-wetting the tip. By
checking the pre-wet function, the tip will aspirate and dispense an appropriate
volume 3 times, before aspirating the desired volume.
Polypropylene is basically hydrophobic (repels water), pre-wetting the interior surface,
reduces this hydrophobicity, allowing a more accurate aspirate.
Experience has shown, repeated use of the tips with ultrasonic washing, reduces this
surface characteristic even more. The caveat is that more liquid will adhere to the tip
exterior, thus the slow withdrawal function is of value. If the tip set is
allowed to dry out, the sequence starts all over. These are small variations that
have been observed. They may or may not have a noticeable effect on all applications.
2.0 Pipeline Pipetting
As described elsewhere, the long narrow portion of the Quadra 450µL tip, may be
used for pipeline pipetting. This allows aspirating several reagents sequentially,