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PIPETTING OF HETEROGENEOUS SAMPLES
(deproteinization in blood glucose determination, for example)
Use steps 1 and 2 of the forward technique to fill the tip with blood.
Wipe the tip carefully with a dry clean tissue.
1. Immerse the tip into the reagent and depress the push button to the first stop, making sure
the tip is well below the surface.
2. Release the push button slowly to the ready position. This will fill the tip. Keep the tip in
the solution.
3. Depress the push button to the first stop and release slowly. Keep repeating this procedure
until the interior wall of the tip is clear.
4. Finally, depress the push button all the way to the second stop to completely empty the tip.
CALIBRATION
All Finnpipettes are factory calibrated and adjusted to give the volumes as specified with
distilled or deionized water. The pipettes are constructed to permit re-adjustment for liquids of
different temperature and viscosity.
DEVICE REQUIREMENTS AND TEST CONDITIONS
An analytical balance must be used. The scale graduation value of the balance should be
chosen according to the selected test volume of the pipette:
Volume range
readable graduation
under 10 µl
0.00 1 mg
10-100 µl
0.01 mg
above 100 µl
0.1 mg
Test liquid: Water, distilled or deionized, “grade 3” water conforming ISO 3696. Tests are done
in a draft-free room at a constant (±0.5°C) temperature of water, pipette and air between 15°C
to 30°C. The relative humidity must be above 50%. Especially with volumes under 50 µl the
air humidity should be as high as possible to reduce the effect of evaporation loss. Special
accessories, such as the evaporation trap, are recommended.
PROCEDURE TO CHECK CALIBRATION
The pipette is checked with the maximum volume (nominal volume) and with the minimum
volume. A new tip is first pre-wetted 3-5 times and a series of ten pipettings is done with both
volumes. A pipette is always adjusted for delivery (Ex) of the selected volume.
Procedure:
1. Do 10 pipettings with the minimum volume.
2. Do 10 pipettings with the maximum volume.
3. Calculate the accuracy (A) and precision (cv) of both series.
4. Compare the results to the limits in the Table 1.
If the calculated results are within the selected limits, the adjustment of the pipette is correct.
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