28
Weighting:
1. Adjust the desired test volume Vs.
2. Carefully
fi
t the tip onto the tip cone.
3. Fill the tip with test water and expel to waste
fi
ve times to reach a humidity
equilibrium in the dead air volume.
4. Replace the tip. Pre-wet the tip by
fi
lling it once with the test water and
expel to waste.
5. Aspirate the test water, immersing the tip only 2–3 mm below the surface
of the water. Keep the pipettor vertical.
6. Withdraw the pipette vertically and touch the tip against the side wall of
the test water container.
7. Pipette the water into the weighing vessel, touching the tip against the
inside wall of the vessel just above the liquid surface at an angle of 30°
to 45°. Withdraw the pipette by drawing the tip 8–10 mm along the inner
wall of the weighing vessel.
8. Read the weight in mgs (mi).
9. Repeat the test cycle until 10 measurements have been recorded.
10. Convert the recorded masses (mi) to volumes (Vi) by multiplying the mass
with the correction factor Z (Z-values in the table below):
Vi = mi *Z
11. Calculate the mean volume (
v
̄
) delivered:
v
̄
= (
∑
Vi)/10
12. For conformity evaluation calculate the systematic error es of the
measurement:
in
μ
l: es =
v
̄
–Vs
Vs = selected test volume
or in %:
es = 100 (
v
̄
–Vs)/Vs
13. For conformity evaluation calculate the random error of the
measurement:
∑
(Vi –
v
̄
)
2
n = number of
as standard deviation s = n –1 measurement (10)
or as coef
fi
cient of variation CV = 100s/
v
̄
14. Compare the systematic error (inaccuracy) and random error
(imprecision) to the performance speci
fi
cation values in chapter 14., or
to the speci
fi
cations of your own laboratory.
Note:
Systematic error is the difference between the dispensed volume
and the selected test volume. Random error is the scatter of the dispensed
volumes around the mean of the dispensed volume. (ISO 8655-1.)
Note:
Biohit speci
fi
cations are achieved in strictly controlled conditions (ISO
8655-6). Users should establish acceptable maximum permissible errors
based on the
fi
eld of use and the accuracy requirements placed on the
pipette (ISO 8655-1).
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