Metrohm 756 KF Coulometer - Manual (Page 21)

2.8 Optimal working conditions
756/831 KF Coulometer, Instructions of Use 13
2.8.2 Reagent exchange
In the following cases the electrolyte solutions should be exchanged:
• When the titration vessel is too full.
• When the capacity of the reagent is exhausted.
• If the drift is too high and shaking the cell does not result in any
improvement.
• If a two-phase mixture is formed in the titration vessel. In this case
only the sample phase can be aspirated off, see also page 25.
• If during the determination the error message
"
check generator
electr.
" appears (see page 105).
Removal of the used electrolyte solutions from the cell is most easily
carried out by aspiration as it is not necessary to disassemble the
cell.
If strong pollution occurs the cell can be rinsed with a suitable sol-
vent which should also be aspirated off.
A Dosino or Titration Stand 703 can be used to aspirate the electro-
lyte solutions, see pages 114ff.
For the generator electrode with diaphragm the catholyte should be
exchanged approx. once a week. Extended use may cause darken-
ing of the catholyte and yellow participation in the cathode com-
partment. An unpleasant smell indicates the need for catholyte ex-
change also.
2.8.3 Indicator electrode
A new indicator electrode may require a certain running-in period for
the formation of the surface. This may cause unusually long titration
times and measurement results which are too high. These phenom-
ena vanish after a short period of use. In order to speed up the run-
ning-in of a new indicator electrode the Coulometer can be condi-
tioned overnight, for example.
A polluted indicator electrode can be carefully cleaned with an abra-
sive cleansing agent (aluminium oxide (6.2802.000 Polishing Set) or
toothpaste). After cleaning it should be rinsed with ethanol.
The two Pt wires of the indicator electrode should be as parallel to
one another as is possible. Check on insertion.