Metrohm 817 Bioscan - Manual (Page 59)

4.4 Optimization of the measuring potential
817 Bioscan
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4.4 Optimization of the measuring potential
An optimization of the measuring potential for amperometric detection
may bring benefits in the following situations:
a) The sensitivity of the detection of the analyte is to be increased
against the background signal.
b) The selectivity of the detection is negatively affected by the analyte
peak overlapping with a second substance peak that has not been
optimally separated by chromatography.
If there are no suitable literature data available, this requires the re-
cording of a voltammogram. This is a curve showing the relationship
between the given potential and the measured current. It is characteris-
tic for individual chemical substances or even whole classes of sub-
stances.
There are two different types of voltammograms, each of which is suit-
able for solving a different problem: a hydrodynamic voltammogram
and a scan voltammogram.
A hydrodynamic voltammogram is made of several chromatograms
recorded in the DC mode. This involves recording a chromatogram of
the substance under investigation, dissolved in eluent, at a constant po-
tential. The potential is now varied several times and the process is re-
peated. Finally the height of the current peak obtained is evaluated and
plotted against the particular potential. Fig. 12 shows a schematic ex-
ample of such a hydrodynamic voltammogram:
Fig. 12: Example of a hydrodynamic voltammogram of a substance (A)
with the additional presentation of the measured values for the
pure eluent (B)
This method is advantageous if the analyte is not present in a pure
form. It also provides more realistic information about the signal/noise
ratio and the selectivity towards overlapping peaks.
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