Metrohm 757 VA Computrace - Manual (Page 178)

8 Troubleshooting
757 VA Computrace – Software
168
4. Has the electrode been conditioned (e.g. by using Condition-
ing cycles and Cleaning potential ) ?
5. If the concentration to be determined is considerably higher
than expected: reduce sample volume.
6. The background current is normally higher if RDE is used in
place of MME; a background current of several 100 nA is
possible.
Curves with high noise
With all MME types:
1. Have stirring or degassing been switched off during the
measurement?
2. Check contact between needle and capillary. If necessary,
clean the MME (see Hardware Manual).
3. Check tapping mechanism on stand. If tapping strength is too
weak, turn corresponding slotted screw on the valve block
during operation in an anticlockwise direction until a drop falls
each time the tapper is triggered (see Hardware Manual).
4. Electrolyte solution too old: make up a new one. Its working
life with organic additives may be as short as 1 day or less.
With DME/SMDE:
1. If the electrode drops irregularly: check the MME.
Adjust sealing needle. If necessary, change capillary or re-
place sealing needle (see Hardware Manual).
2. If the electrode drops much too quickly: reduce the Voltage
step time on the Voltammetric tab of the EDIT WORKING
METHOD PARAMETERS window.
With
HMDE:
1. If the electrode surface is overcharged: check deposition po-
tential and time.
2. If no drops are at the capillary: change the capillary or replace
sealing needle (see Hardware Manual).