TomTec QUADRA 4 - Dispensing Techniques; Mixing Techniques; Titration Method

Quadra 4 Operator Manual
Tomtec
176
using 10-15µL air gaps, for separation. The separating air gap must remain within
the narrow portion of the tip, which has a capacity volume of 90µL.
As an example, assume the protocol requires 50µL of buffer, 30 microliters of
reagents A, 20 microliter of reagent B, and 10µL of drug compound. The Quadra 4
shuttle will present these devices in order to the pipettor head. First is to aspirate
50µL of buffer, then 10µL of air gap, followed by 30µL of reagent A, then 10µL of air
gap, then 20µL of reagent B, then 10µL air gap and finally 10µL of compound. In
addition to speed of throughput, the method can improve the accuracy of pipetting.
The higher volume buffer is used to wash out the smaller critical volume of drug
compound.
3.0 Dispensing
Normally the speed of dispensing is not critical. However, the 3 speeds are
provided. By making the dispense at the top of the well, any separating air gaps do
not create bubbles. These may have an effect on some plate readers.
After a piston actuated dispense, there may be drops hanging on the tips. The
Quadra 4 software provides several means of returning these drops to the contents
of the well. The simplest and most effective method is a timed dispense function.
This is made at the clear height of the well, as set in the database. Low air pressure
from the internal air tank is discharged through the tips, clearing the orifice.
Another method is tip touch off. If this is checked, the stage will move the plate over
to cause the tip to touch the sidewall of the well. This distance is defined in the
plate database.
The third option is to dip the tip back into the liquid contents of the well to allow
surface tension to remove the clinging drop. The choice of the methods is
dependent on the application.
4.0 Mixing
In many applications, it is desired to mix the contents of the well, following a
dispense. The Quadra 4 provides several mixing functions.
5.0 Titration
This is simply making multiple aspirate and dispense moves. It can be
accomplished with any of the Quadra 4 pipettor heads. It is recommended that the
aspirate be made from the bottom of the well, and dispensed at the top to turn the
liquid over. Aspirate approximately 70% of the well contents volume each time.