12
12. TESTING THE PERFORMANCE AND RECALIBRATION
It is recommended to check the performance of your Biohit
m
LINE
pipettes regularly (e.g. every 3 months) and always after in-house
maintenance. However, the user should establish a regular testing
routine for their pipettes with regard to accuracy requirements of
the application, frequency of use, number of operators using the
pipette, nature of the liquid dispensed and the acceptable maxi-
mum permissible errors established by the user. (ISO 8655-1.)
12.1. Testing the performance
Performance testing should take place in a draught-free room at
15 - 30°C, constant to +/- 0.5°C and humidity above 50%. The
pipette, tips and the test water should have stood in the test room
a suf
fi
cient time (at least 2 hours) to reach equilibrium with the
room conditions. Use distilled or deionised water (grade 3, ISO
3696). Use an analytical balance with a readability of 0.01 mgs.
(ISO 8655-6.)
Weighing
1. Adjust the desired test volume V
s
.
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 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 pipette vertical.
6. Withdraw the pipette vertically and touch the tip against the
inside 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 (m
i
).
9. Repeat the test cycle until 10 measurements have been
recorded.
10. Convert the recorded masses (m
i
) to volumes (V
i
)
V
i
= m
i
Z
Z = correction factor (Table 1)
11. Calculate the mean volume (
v
̄
) delivered:
v
̄
= (
∑
V
i
)/10
12. For conformity evaluation calculate the systematic error e
s
of
the measurement:
in
μ
l:
e
s
=
v
̄
- V
s
V
s
= selected test volume
or in %:
e
s
= 100 (
v
̄
- V
s
)/V
s
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