Metrohm 756 KF Coulometer - Manual (Page 16)

2.5 Generator electrode with diaphragm
756/831 KF Coulometer, Instructions for Use 8
2.5 Generator electrode with diaphragm
The 6.0344.100 generator electrode with diaphragm should be used
when your samples contain ketones and aldehydes because special
reagents for aldehydes and ketones are only available for generator
electrodes with diaphragms.
If your reagent has a low conductivity, e.g. if you have had to add
chloroform because of the solubility of the sample then you should
use the generator electrode with diaphragm as first choice.
It can also be recommended when you require very good accuracy
in the lowest trace analysis ranges.
2.5.1 Reagents
Reagents for coulometric water determination with generator elec-
trodes with diaphragms consist of an anode solution (anolyte), which
is filled into the titration vessel and a cathode solution (catholyte)
which is filled into the generator electrode.
Special reagents must be used for water determination in ketones
and aldehydes; please refer to the reagent manufacturer's instruc-
tions.
2.5.2 Cleaning
The electrolyte solution can normally be exchanged without any spe-
cial cleaning of the parts being necessary. If cleaning is necessary
then care should be taken that the Pt grid of the generator electrode
is not damaged.
Resinous deposits on the diaphragm:
Hang the generator electrode vertically from a support rod, fill with
conc. HNO
3
and allow to stand overnight. Rinse with water followed
by ethanol.
Pollutants containing oil:
Clean with a solvent (e.g. hexane) and then rinse with ethanol.
Salt-like deposits:
Clean with water and then rinse with ethanol.
Cleaning (rinsing) the diaphragm:
Fill the cathode compartment of the generator electrode with metha-
nol and allow the filling to drain out. Repeat the process 2-3 times.
This process should also be carried out when the electrode has
been cleaned as described above.
Dry all parts thoroughly after cleaning. A hot-air blower can be used
for this. If the parts are dried in a drying oven take care that the tem-
perature does not exceed 70°C (plastic components!).