Quadra 4 Operator Manual
Tomtec
21
Section II - Operational Functionality
Pipetting System
The pipettor pistons are driven by a software controlled stepper motor. To provide
precise control it requires 400 half steps of the motor to make one revolution. This in
turn drives the syringe pistons aspirating or dispensing fluid. On the 96SV and 384 head
the pistons extend to the bottom of the pipette tips. This provides positive displacement
pipetting, essential for sub-microliter dispensing. The 450µL disposable tip head is an air
displacement system, providing up to 450µL dispensing.
Upon initialization, the stepper motor drives the piston up to actuate a photo sensor.
This is the home position for the volume counter. It then counts down to the zero volume
position for the pistons. Aspirate and dispense volumes are made by counting up or
down. You must always dispense an equal volume that has been aspirated. If you try to
dispense more than you have aspirated, "Pump Range" error will occur. If you do not
dispense the full amount aspirated, the accumulation will again cause "Pump Range"
error.
There are four speeds for the head motor. It is recommended that you always use speed
3, unless you are aspirating or dispensing viscous liquids. These may not flow through the
tip orifice in the time allowed at speed 3, especially, with the 0.015 inch diameter of the
small volume tips on the 96SV and 384 head.
The 450µL head has the ability to count below zero volume to remove the tips. There is a
software number that determines this function. It drives the tip stripper plate down to or
below the "O" ring to strip the tips from the tip pins. Each time the stripper plate moves
down, it applies a very light coating of lubricant to the tip pin "O" rings.
When loading tips, a sensor detects whether the tips have been fully sealed, thereby
preventing error in the pipetting volumes. If this sensor does not actuate, the stage will try
three times to load the tips properly. If it fails after the third time you are asked to use the
manual lubricator on the tip pin "O" rings. If this occurs frequently it is time to replace the
internal lubrication pad.
The design of the Quadra tips is unique. The long narrow portion (90µL) allows pipeline
pipetting, permitting you to aspirate several reagents sequentially using small air gaps for
separation. This, combined with the multiple stations on the Quadra 4 shuttle, means all of
the reagents can be added in one pass. The larger volume buffer can be used to wash out
the smaller volume of the compound. The 450µL volume of the Quadra tips also permits the
larger tasks, such as Solid Phase Extraction, Liquid/Liquid Extraction, or Protein Precipitation.
The Quadra tips (PN 196-205) are available with a standard orifice size 0.036”, as both
sterile, and non sterile. The Quadra tips are retained in their rack. This permits handling
them as a single unit, not individual tips. They may be used, shucked as a unit, and
reused.
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