Metrohm 817 Bioscan - Manual (Page 61)

4.4 Optimization of the measuring potential
817 Bioscan
53
The final aim is to select a suitable potential for use as the measuring
potential for pulsed amperometric detection. This means that usually a
compromise has to be found between the highest possible sensitivity,
selectivity and reproducibility:
Higher potentials can increase the sensitivity; however, more sub-
stances can also be determined and this reduces the selectivity. In or-
der to achieve high reproducibility, a potential from a flatter segment
near to the maximum of the analyte voltammogram should be selected.
In the example shown in Fig. 12, E
1
was a potential determined in this
way.
During the determination of the optimum measuring potential the
constancy of the parameters pH and temperature as well as the
pulsation-free eluent supply are important (see Section 4.2).
Hydrodynamic
voltammogram
Scan
voltammogram
Situation
• Selectivity for an inadequate
IC-separation is to be im-
proved
• Sensitivity of a substance
peak is to be increased
Requirement
• Substance can be investi-
gated in the mixture
• IC parameters must be
known
• Substance must be present in
a pure form
Advantages
• "Chromatographic" condi-
tions, i.e. a direct check of
selectivity and sensitivity is
possible
• Several substances can be
investigated at the same time
• Less time needed for single
substances
Disadvantages
• More time required for a
single substance
• Possible formation of an oxide
layer on the working electrode