Quadra 4 Operator Manual
Tomtec
163
Section IV – Pipettor Heads
The Quadra 4 design will accommodate different pipettor heads for specific applications.
They are all interchangeable by the user. Each pipettor head is secured with 4 bolts. The
head plugs into the back plane for its electrical and software connections. Each head is
then manually aligned to the stage. This can be easily accomplished in less than 30
minutes, start to finish. Each pipettor head and its use is described individually, since
any pipettor head may be placed in your Quadra 4.
1.0 Quadra 4 Air Displacement Pipettor Heads
1.1 Quadra 450µL Disposable Tips
This is the primary pipettor head for the Quadra 4. It is the dominant pipettor for general
applications with a long history of reliability and dependable operation. It has several
primary advantages. First is the 450µL volume of the disposable tip. Secondly, the tips
can reach the bottom of the SBS deep-well microplates. The third advantage is the
ability to blow pressurized air through the tips, under software control. This function
permits the combination of aqueous and organic pipetting, without having to change
tips between each liquid. It also permits non- contact dispensing. Another function is to
clear the residual retained in the tip by capillary action, when pipetting small volumes.
The pipettor pistons are driven by a software controlled stepper motor. The motor
requires 400 steps to make one revolution. Each revolution of the motor moves the
individual 96 pistons 0.0625 inches. This distance multiplied by the piston diameter
equates to software steps per microliter.
Each individual piston has a small hole through it. This small hole is connected with
silicon rubber tubing, through a motorized pinch clamp, and then to an internal tank
that is pressurized with regulated air pressure from 0 to 5 psi. When the pinch point is
closed, all pistons act as air displacement pipettors, when the pinch point opens, air
pressure can blow through the tip orifices. This offers a number of distinct operating
advantages to the Quadra 4 user.
1.2 Organic to Aqueous Pipetting
To pipette organic liquids, it is first necessary to fill the tip head space with the organic
vapors to prevent dripping. To switch back to pipetting aqueous liquids, it is necessary
for competitive instruments to change tips, to provide accuracy. The Quadra 4 program
simply opens the pinch valve to clear the organic vapors. Now aqueous liquids may be
pipetted with accuracy. This is a common application in many sample preparation
techniques, solid phase extraction, liquid/liquid, and protein precipitation.
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