Metrohm 757 VA Computrace - Manual (Page 182)

8 Troubleshooting
757 VA Computrace – Software
172
Standard addition peaks displaced
With all types of electrodes:
1. Standard solutions have been made too acidic.
2. Buffering capacity of the electrolyte is not sufficient: increase
electrolyte volume.
3. 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 HMDE:
1. If HMDE is used potential displacements of more than 20…30
mV are often normal and have to be accepted; particularly in
adsorption voltammetry.
With RDE/SSE:
1. Electrode surface overcharged: reduce sample volume.
No addition
With all types of electrodes:
1. Has the correct standard solution been used or is the concen-
tration of the solution too low: increase the volume of the
standard addition solution or use a higher concentration or
reduce the sample amount accordingly.
2. If organic components are present: carry out a UV digestion
or other suitable sample preparation.
3. Concentration of the analyte is too high: dilute.
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 HMDE:
1. Addition solution with metal complexing solution (time reac-
tion).
Spikes / signal jump in voltammogram
1. For MME: check the electrode.
2. Reduce the dynamic range of the potentiostat (see Potentio-
stat, section 3.3).