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Calibration
•
Calibrate the pipette for the liquid. If the liquid has a specific gravity
and vapor pressure equivalent to distilled water, calibrate using "EASY"
CAL mode. Otherwise, use "CALC" mode.
• Pre-wet the pipette tip. Aspirate and dispense a few times before
aspirating the liquid to increase humidity within the tip, reducing
sample evaporation that results in lower dispense volumes in initial few
pipettings. The need to pre-wet increases when working with liquids with
high vapor pressure and/or high surface tension.
• Immerse tips fully. Tips should be immersed approximately 1/4 inch
(approx. 0.6 cm) below the liquids meniscus and away from the container
surfaces to avoid aspiration of air and excess droplets clinging to the
outside of the tip.
• Discard a primer volume. When the motor changes from aspiration to
dispense, the percentage of error is greater in the first dispense than in
subsequent dispenses.
• Pause consistently. It takes a moment for the liquid in the tip to finish
moving. Pause with the tip in the liquid for about one second after
aspirating the sample to allow the liquid to finish moviing into the pipette
tip after the pipette stops. Otherwise, the volume will be lower than it
should.
• Aspirate slowly, dispense quickly. As a general rule, pipette liquids,
especially viscous liquids, at a slower speed to ensure accurate
pipetting. Dispense aqueous solutions at faster speeds to expel liquid
more accurately.
Note: Viscous liquids should be dispensed slowly.
• Tip touch. During the dispensing of a liquid, touch the tip against the
side of the receiving container to prevent any liquid from remaining on
the tip.
• Discard final dispense. When accurate dispensing of several
increments of liquid are needed, discard the last increment. The
cumulative percentage of error from previous increments carries to the
last volume. (i.e. The pipette aspirates 100 µl and dispenses 20 µl five
times, and if each of the first four dispenses were off by +1.0 µl, then the
last dispense is missing 4 µl before you even dispense it).
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