Metrohm 797 VA Computrace - Manual (Page 282)

9 Troubleshooting
797 VA Computrace – Software
270
deposition even with concentrations ρ > 100 μg/L (e.g. DP voltam-
metry at the HMDE or also at the DME).
The effects of a deposition time which is too long are shown by the
following two examples:
• Nickel and cobalt determination in the trace region
by cathodic adsorption stripping voltammetry (with
dimethylglyoxime complexes)
Prolongation of the deposition time from 30 s to 120 s (kee-
ping all other measurement parameters constant) leads to non-
linear standard additions and in the case of nickel also to shifts
in the peak maximum:
Deposition time: 30 s Deposition time: 120 s
Analysis solution: 20 μg/L Ni; 20 μg/L Co
Supporting electrolyte: 0.1 mol/L NH
4
Cl/NH
3
; pH = 9.3
5⋅10
-4
mol/L dimethylglyoxime (DMG)
Standard addition: with 200 ng Ni / 200 ng Co
Electrode: HMDE
• Mercury determination at the gold electrode
On prolongation of the enrichment time from 30 s to 240 s,
side peaks appear during standard addition:
Enrichment time: 30 s Enrichment time: 240 s
Co
Ni
Co
Ni