Metrohm 739 Exchange unit - Manual (Page 37)

4. Stopcock
6.3013.XXX and 6.3014.XXX Exchange Units, 8.110.1346
37
4. Stopcock
Two stopcocks are available: The 6.1542.020 PCTFE/PTFE
stopcock and the 6.1542.010 ceramics stopcock.
Use the ceramics stopcock if hard crystals can precipitate from
your solution or if your dosing is continuously running. If the pre-
cipitate is soft and if you use the Exchange Unit at greater time
intervals, we recommend the PCTFE/PTFE stopcock.
PCTFE/PTFE stopcocks are worn out after a certain time. They
have to be replaced more frequently than ceramics stopcocks.
For the following reagents and applications, we recommend:
6.1542.020
PCTFE/PTFE
6.1542.010
ceramics
Acids, aqueous l l
Alkali, aqueous l
Continuous running l
EDTA l
HClO
4
in acetic acid l l
Iodine, solution l
Karl Fisher reagent l
KOH in ethanol l
Organic solvents l
Permanganate, KMnO
4
l
Silver nitrate, AgNO
3
l l
TBAOH l
Thiosulphate, Na
2
S
2
O
3
l l
What can you do with a blocked stopcock?
1. Remove stopcock from the handle of the Exchange Unit.
2. Soak stopcock in appropriate solvent. Use
hot water for aqueous solutions;
the corresponding organic solvent for non-aqueous solutions;
methanol, than water, than methanol for KF reagent.
3. If you can turn the stopcock, remount it onto the Exchange
Unit.
You may open the stopcock opening the screw nut. The polished surfaces
of the cock plates must be without damage.
Mount the dried parts and do not touch the polished surface of the cock
plates.