Thermolab Sartorius MC210, Руководство пользователя

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26
Factors affecting the accuracy of air
displacement pipettes
Temperature
The most important factor in pipetting accuracy is the liquid temperature. The fig-
ure below shows the change in volume when the liquid has a different tempera-
ture than the pipette and air. If the temperature of the liquid, pipette and air is the
same, the accuracy is not significantly affected.
Density
Density is the mass/volume ratio of the liquid. The density varies according to the
temperature and air pressure. Typically, the density of water is 0.996 kg/dm3, for
ethanol 0.79 kg/dm 3 and for sulfuric acid (H
2
SO
4
) 1.85 kg/dm 3 .
Altitude
The geographic altitude affects the accuracy through the air pressure. The air pres-
sure decreases at higher altitudes and the conversion factor Z decreases as well.
The boiling point of some liquids can also change to quite close to room tempera-
ture, increasing the evaporation loss dramatically.
Temperature
Accuracy with different liquid
temperatures. Calibration at 22°C.
6
4
2
0
-2
-4
-6
10.0
20.0
30.0
Liquid temperature °C
Accuracy %
1
0.8
0.6
0
0.8
1.0
1.2
Liquid density kg/dm 3
A
c
c
u
ra
c
y %
Accuracy with different liquid density.
Calibration with distilled water.
0.4
0.2
-0.2
-0.4
-0.6
1.4
1.6
1.8
Density
Altitude
Accuracy at different altitudes.
Calibration at sea level.
0.5
0.25
0
-0.25
0 m
1000 m 2000 m
Altitude above sea level
A
c
c
u
ra
c
y %