Checking the volume (calibration) – BrandTech Scientific Titrette User Manual
Page 46
46
Depending on use, we recommend that gravimetric testing of the instrument be carried out every 3-12
months. Set the 10 ml instrument to calibrate to 3 decimal places (page 61). This time frame should be
adjusted to correspond with individual requirements. The complete testing procedure (SOP) can be down-
loaded at www.brand.de. In addition, a function test can also be carried out over shorter time spans, for
example by titration against a standard. For GLP- and ISO-compliant evaluations and documentation, we
recommend the EASYCAL
™
calibration software from BRAND. A demo version can be downloaded from
www.brand.de.
1.
Preparation of the instrument
Clean the burette (see 'Cleaning', page 54), fill it
with distilled H
2
O and then prime it carefully.
2.
Check the volume
a) Dispense 5 drops into a separate receptacle and
wipe off the titrating tube tip.
b) Press the CLEAR key to set the display value to
'zero'.
c) 10 dispensed amounts in 3 volume ranges
(100%, 50%, 10%) are recommended.
d) Turn the hand wheels with both hands without
stopping until the test volume is shown in the
display. Wipe off the titrating tube tip.
e) Weigh the dispensed amount on an analytical bal-
ance. (Please follow the operating manual from
the balance manufacturer.)
f) Calculate the dispensed volume. The Z factor
takes account of the temperature and air buoy-
ancy.
3.
Calculation
Checking the Volume (Calibration)
Gravimetric volume testing according to DIN EN ISO 8655-6 (for measurement conditions, see 'Error
Limits', page 45) is performed as follows:
x
i
= Weighing results
n = Number of weighings
Z = Correction factor
(for example 1.0029 µl/mg at 20 °C, 1013 hPa)
Mean volume
* Calculation of accuracy (A %) and coefficient of variation (CV %):
A % and CV % are calculated according to the formulas for statistical control.
V
0
= Nominal volume
100 s
V
CV% =
Σ (x
i
– x)
2
n – 1
s = Z ·
V – V
0
V
0
A% = · 100
Mean value x =
Σ x
i
n
Mean volume V = x · Z
Accuracy*
Standard Deviation
Coefficient of Variation*