Metrohm 871 Advanced Bioscan - Manual (Page 29)

3.4 Optimization of the measuring potential
871 Advanced Bioscan / Instructions for Use 8.871.1003
21
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 the maximum of the analyte voltammogram should be selected. In
the example shown in Figure 6, E
1
would be such a potential deter-
mined in this way.
Hydrodynamic Scan
Situation • Selectivity for an inadequate • Sensitivity of a substance
voltammogram voltammogram
IC-separation is to be im-
proved
peak is to be increased
Requirement •
pure form
Advantages
tions, i.e. a direct check of
• Several substances can be
substances
Disadvantages
de
Substance can be investi-
gated in the mixture
• Substance must be present
in a
• IC parameters must be
known
• "Chromatographic" condi- • Less time needed for single
selectivity and sensitivity is
possible
investigated at the same
time
• More time required for a
single substance
• Possible formation of an ox-
ide layer on the working
electro
During the determ ination of the optimum measuring potential the con-
stancy of the parameters pH and temperature as well as the pulsation-
free eluent supply are important (see Section 4.2).