Peak on highly curved baseline – Metrohm 757 VA Computrace User Manual

Page 187

8.6 Voltammetric problems

757 VA Computrace – Software

177

mL analysis solution] would also give a clearly defined current
peak for CuCl

–

Supporting electrolyte:

without EDTA

with EDTA (0.001 mol/L)

Analysis solution:

25 µg/L Cu; 10 µL HCl 30%

Standard addition:

with 250 ng Cu

Electrode:

HMDE (enrichment 90 s at –600 mV)

Peak on highly curved baseline

If peaks lie on a highly curved baseline, the first attempts at recti-
fication should involve chemical or measurement technique coun-
termeasures to eliminate the adverse effect on the peak evalua-
tion due to the highly curved baseline. Such measures include
longer purging times (see Oxygen interference), changing the pH
value, changing the supporting electrolyte concentration, modify-
ing or changing the supporting electrolyte, use of complexing
agents (see Complex formation), longer enrichment times and
changing the measurement technique.
If the curvature of the baseline can not or only partially be elimi-
nated by the above measures, the 757 VA Computrace offers the
possibility to approximate a curved baseline by selecting

Polyno-

mial

Exponential

for the baseline

Type

(see Baseline, section

5.2).
A further possibility to evaluate peaks on curved baselines in-
volves the background subtraction after measuring a blank solu-
tion, in particular when the curved baseline can be clearly attrib-
uted to the supporting electrolytes (see Determination, section
5.2).

CuCl

2–

CuCl

–

CuEDTA