Antec Scientific ROXY Exceed, User Manual, Page: 77 / 126

Chapter 7 Optimization of working potential 77
flow rate not only affects temporal peak width and analysis time but also
peak height. Also the background signal is sensitive towards fluctuations
in the flow rate. Therefore, it is important to use a pulse-free solvent deliv-
ery system.
Construction of a hydrodynamic voltammogram
Before a hydrodynamic voltammogram can be obtained, the chromato-
graphic conditions should be optimized. Then the following steps are
taken:
1. A solution of the analyte at a concentration between 1 - 100
µmol/L, is prepared in mobile phase.
2. The electrochemical potentiostat is stabilized in the DC mode at a
high potential. After stabilization the background current is read
from the display of the potentiostat (I-cell) and the noise is
measured.
3. The run is started by injecting the compound. When at the high
working potential no signal is obtained, it may be concluded that
the compound is not electrochemically active. In such a case
derivatization of the compound may be an option.
4. If a peak is measured, the working potential is decreased by 50 or
100 mV and step 2 to 4 is repeated until the lowest potential
setting (Fig. 34).
5. The peak heights and the background currents are plotted against
the working potential (Fig. 27).
The working potential which gives the best sensitivity is obtained by
plotting the signal-to-noise ratio against the working potential.
Fig. 34. Construction of a hydrodynamic voltammogram for nor-
epinephrine. Chromatograms are obtained at cell potentials ranging from
1.0 V (back) to 0.4 V (front), with 100 mV steps.