BrandTech Scientific Dispensette III - Manual (Page 46)

46
Depending on use, we recommend that gravimetric testing of the instrument be carried out every 3-12
months. This time frame should be adjusted to correspond with individual requirements. The complete
testing procedure (SOP) can be downloaded at www.brandtech.com. In addition, you can also carry out
function checks at shorter intervals, e.g. dispensing the nominal volume into a volumetric test flask (volu-
metric flask with 3 marks, DAkkS calibrated). For GLP- and ISO-compliant evaluations and documenta-
tion, we recommend the EASYCAL
™ calibration software from BRAND. A demo version can be down-
loaded from www.brandtech.com.
x
i
= results of weighings
n = number of weighings
Z = correction factor
(e. g., 1.0029 µl/mg at 20 °C, 1013 hPa)
V
0
= nominal volume
Mean volume
V – V
0
V
0
A% = · 100
Σ (x
i
– x) 2
n – 1
s = Z ·
Mean value x =
Σ x
i
n
Mean volume V = x · Z
Standard deviation Coefficient of variation
Checking the Volume (Calibration)
100 s
V
CV% =
Gravimetric volume testing according to DIN EN ISO 8655-6 (for measurement conditions, see 'Error
Limits', page 45) is performed as follows:
1.
Preparation of the instrument
Clean the instrument ('Cleaning', page 48-51),
fill it with distilled H
2
O and then prime it carefully.
2.
Check the volume
a) 10 dispensing operations with distilled H
2
O in
3 Volume ranges (100 %, 50 %, 10 %) are
recommended.
b) For filling pull up the piston gently until the
upper stop of the volume set.
c) For discharge depress piston slowly and
steadily without force until the lower stop.
d) Wipe off the tip of discharge tube.
e) Weigh the dispensed quantity on an analytical
balance. (Please follow the operating manual
of the balance manufacturer.)
f) Calculate the dispensed volume. The Z factor
takes account of the temperature and air
buoyancy.
3.
Calculations
Accuracy