Metrohm 757 VA Computrace - Manual (Page 181)

8.6 Voltammetric problems
757 VA Computrace – Software
171
With RDE/SSE:
1. The background current is too high: repolish the electrode.
2. The
Deposition time is too long: reduce the time.
3. Is the Deposition potential correct?
Double peak
With all types of electrodes:
1. Organic components interfere with the analysis: carry out a
UV digestion or other suitable sample preparation.
2. Electrolyte solution too old: make up a new one. Its working
life with organic additives may be as short as 1 day or less.
3. If a second element is present at the same potential: add this
element to the sample and carry out the analysis again. If the
second peak has become higher then the second element is
present. Might it be possible to selectively mask this second
element with a complex former?
4. For Cu: work without chlorides in the electrolyte or increase
the chloride concentration massively.
5. Has any substance formed a precipitate in the measuring
vessel (e.g. lead perchlorate standard with KCl as electro-
lyte)?
6. Try out eluents with different compositions (addition of com-
plex formers).
7. Check method parameters.
8. Try another measurement mode like AC1. If one substance is
reversible and the second one irreversible, only the reversible
substance is detected by AC1.
With MME:
1. Check MME. If necessary, change capillary or replace sealing
needle (see Hardware Manual).
With RDE/SSE:
1. Check RDE and polish if necessary (see Hardware Manual).