8 – LABNET LABPETTE FX PIPETTORS
Aspirating High-density Liquids
When pipetting liquids of higher viscosity or lower surface
tension than water (e.g., sera or organic solvents), a film of
liquid may be formed on the inside of the pipet tip which
may produce erroneous results. As the film remains relatively
constant in successive pipetting operations with the same
tip, this error can be eliminated by pre-rinsing the tip and
allowing a film to form before transferring the first sample.
This is achieved by aspirating a sample and dispensing it
back into the same vessel. Allowing a film to form prior to
sampling ensures optimal accuracy and repeatability.
This pre-rinsing operation should be repeated when
the volume to be aspirated is changed or when a new pipet
tip is used.
NOTE:
Normally the degree of error resulting from viscous
liquids is negligible if pipetting is performed slowly and
carefully, however can be minimized further by holding the
pipet tip in position for at least 2 seconds after aspiration
to allow the liquid time to react to the change in pressure
before it is dispensed.
If the above method does not result in accurate values,
recalibrate the pipettor in accordance with Section 9.
It is recommended to record recalibration and correction
values, in order to facilitate reverse calibration to a standard
liquid.
9. Checking Pipetting Accuracy Parameters
and Pipettor Recalibration
The pipettors have been factory-calibrated using gravimetric
methods with manufacturer pipet tips and distilled water,
in accordance with ISO 8655 guidelines
for the liquid volume drawn by the pipettor according to
the values given (Section 5). The pipettors are designed to
enable recalibration and adaptation to different pipetting
techniques and liquid properties (e.g., temperature, density,
and viscosity). Periodic checks of the operation of the
pipettor are recommended at least once per year. Frequency
of checks should be increased depending on workload,
sterilization or autoclave processes, and frequency of
replacement of component parts.
If during pipettor operation the accuracy error exceeds the
permissible value given in the table in Section 5, pipettor
recalibration should be carried out. Recalibration of the
pipettor involves adjusting the settings according to the
table on page 10.
