6
FORMULAS FOR CALCULATING RESULTS
Conversion of mass to volume
V = (w + e) x Z
V = volume (µl)
w = weight (mg)
e = evaporation loss (mg)
Z = conversion factor for mg/µl conversion
Evaporation loss can be significant with low volumes. To
determine mass loss, dispense water to the weighing
vessel, note the reading and start a stopwatch.
See how much the reading decreases during 30 seconds
(e.g. 6 mg = 0.2 mg/s). Compare this to the pipetting time
from tareing to reading. Typically pipetting time might be 10
seconds and the mass loss is 2 mg (10s x 0.2mg/s) in this
example. If an evaporation trap or lid on the vessel is used
the correction of evaporation is usually unnecessary.
The factor Z is for converting the weight of the water to
volume at test temperature and pressure. A typical value
is 1.0032 µl/mg at 22°C and 95 kPa. See the conversion
table on page 8.
Accuracy (systematic error)
Accuracy is the difference between the dispensed
volume and the selected volume of a pipette.
A = V - V
0
A = accuracy
V = mean volume
V
0
= nominal volume
Accuracy can be expressed as a relative value:
A% = 100% x A / V
0
Precision (random error)
Precision refers to the repeatability of the pipettings. It is
expressed as standard deviation (s) or coefficient of
variation (cv)
1
)
(
2
-
-
=
n
V
V
S
i
S
i=1
n
PACKAGE
The FINNPIPETTE PDP is shipped in a specially designed
package containing the following items:
1. The pipette
2. Instruction manual
3. Service tool
4. Calibration certificate
5. Sample of Finntip PDP
s = standards deviation
v = mean volume
n = number of measurements
cv is the relative value of standard
deviation.
cv = 100% x s / v
