Metrohm 817 Bioscan User Manual

Page 61

4.4 Optimization of the measuring potential

817 Bioscan

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

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