Maintenance - Thermo Scientific Finnpipette Guide D'utilisation Et D'entretien

FORMULAS FOR CALCULATING RESULTS
Conversion of mass to volume
V = (w + e) x Z
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 taring to reading. Typically pipetting time might be
10 seconds and the mass loss is 2 mg (10 s x 0.2 mg/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 38.
Inaccuracy (systematic error)
Inaccuracy is the difference between the dispensed volume and the selected volume of a
pipette.
A = V - V A
0
V
V
0
Inaccuracy can be expressed as a relative value: A% = 100% x A / V
Imprecision (random error)
Imprecision refers to the repeatability of the pipettings. It is expressed as standard
deviation (s) or coefficient of variation (cv)
n
S
( V - V
S
=
i
i=1
n 1
-
Standard deviation can be expressed as a relative value (CV) CV = 100% x S / V
When the Finnpipette Digital Multichannel is not in use, make sure it is stored in an upright
position. We recommend a Finnpipette stand for this purpose.
SHORT-TERM CHECKING
The pipette should be checked at the beginning of each day for dust and dirt on the outside
surfaces of the pipette.
Particular attention should be paid to the tip cone. No other solvents except 70 % ethanol
should be used to clean the pipette.
V = volume (µl)
w = weight (mg)
e = evaporation loss (mg)
Z = conversion factor for mg/µl conversion
= inaccuracy
= mean volume
= nominal volume
s = standards deviation
)
2
v = mean volume
n = number of measurements

MAINTENANCE

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