Metrohm 756 KF Coulometer - Manual (Page 41)

3.6 Parameters, key <PARAM>
756/831 KF Coulometer, Instructions of Use 33
0
20
40
60
80
100
Start drift
When the actual drift during conditioning is smaller than the start drift a titration can be
started. The "COND" LED remains on all the time.
Stop drift
The titration is terminated when the EP has been reached and the stop drift is undercut.
For the relative stop drift the drift value at the start of the titration + the relative drift ap-
plies.
Drift correction
If the titration vessel has a blank consumption during conditioning then it must be as-
sumed that this blank consumption will also occur during the titration. In this case a drift
correction should be made. The drift correction is calculated as follows:
Drift correction = Drift value (in ug/min) * Titration time (in min)
With automatic drift correction the drift value at the start of the titration applies. If the drift
value varies greatly then a manual drift correction should be made. The drift value to be
entered should correspond to the mean drift value.
3.6.4 Current at the generator electrode
The current at the generator electrode is set by the parameter "generator I" (under titration
parameters). The steps 400, 200 and 100 mA are possible. With the setting "auto" the
current strength will be automatically reduced in the region of the endpoint. The current
strength will also be reduced if the conductivity of the reagent becomes too low.
Generator electrodes with diaphragm
Work should normally be carried out with automatic switching of the current strength.
Generator electrodes without diaphragm
For generator electrodes without diaphragm the current strength must be sufficiently high
so that only hydrogen is produced at the cathode. If this is not the case then the results
obtained will be too high. We therefore recommend that a fixed current strength of
400 mA is used.
If the conductivity of the fresh reagent is too low and therefore the error message "check
generator electr." appears then a generator electrode with diaphragm should be used.
You can also try to continue to use the generator electrode without diaphragm together
with a different reagent. Ask the reagent manufacturer for more information! It may also
be possible to use a lower fixed current strength, e.g. 200 mA, without obtaining high-bias
results (check with a standard).
Drift in ug/min
Time
Start drift
Cond. Start Titr. End Titr.
Stop drift
Drift
value at
start