Metrohm 757 VA Computrace - Manual (Page 188)

8 Troubleshooting
757 VA Computrace – Software
178
Peak overlapping
If the peak overlapping has reached a critical level at which the
calculated peak height or peak area is falsified by the neighbour-
ing peak, it is advisable to take the overlapping into account by a
change in the baseline calculation. For this, select the
Front end or
Rear end option for the baseline Scope (see Baseline, section 5.2).
If the overlapping is too large, the peak can no longer be evalu-
ated. In this case chemical or measurement technique counter-
measures must be used to attempt to separate these peaks bet-
ter. Possible measures include changing the pH value (see ex-
ample below), changing the supporting electrolyte concentration,
changing the supporting electrolyte, use of complexing agents
(see Complex formation), longer enrichment times and modifying
or changing the measurement technique.
• Determination of lead and thallium
With a supporting electrolyte of pH = 1, Pb and Tl peaks
overlap greatly. Changing the pH to 13 separates the two
peaks. (The separation of lead and thallium can also be
achieved by subsequent electrolysis or in acetate buffer with
EDTA).
Supporting electrolyte: Supporting electrolyte:
pH = 1 pH = 13
Analysis solution: 0.5 mg/L Pb; 1 mg/L Tl
Standard addition: with 10 µg Pb and 10 µg Tl
Electrode: SMDE
Pb
Tl