Metrohm 871 Advanced Bioscan - Manual (Page 27)

3.4 Optimization of the measuring potential
871 Advanced Bioscan / Instructions for Use 8.871.1003
19
3.4 Optimization of t
An optimization of
may bring benefits
a) The sensitivity
against the bac
vity
peak overlappi
optimally separ
If there are no suita
mogram is require
the given potential
dividual chemical s ces.
here are two different types of voltammograms, each of which is suit-
ynamic voltammogram
and a scan voltammogram.
ch a hydrodynamic voltammogram:
he measuring potential
the measuring potential for amperometric detection
in the following situations:
of the detection of the analyte is to be increased
kground signal.
b) The selecti of the detection is negatively affected by the analyte
ng with a second substance peak that has not been
ated by chromatography.
ble literature data available, recording of a voltam-
d. This is a curve showing the relationship between
and the measured current. It is characteristic for in-
ubstances or even whole classes of substan
T
able for solving a different problem: a hydrod
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. Figure 6 shows a schematic ex-
ample of su
I
Figure 6: 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 recommended 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.
The scan voltammogram is recorded in the scan mode. The measur-
ing potential is varied backwards and forwards between two given limits
rent is then measured for each potential.
t a separation column
connected. If you work on trace concentrations of your analyte and
while the analyte is passed through the measuring cell. The actual cur-
The substance under investigation can be dissolved in the IC eluent
used (e.g. 10 ppm Sucrose in 0.1 M NaOH) and a larger amount (e.g.
100 mL) pumped through the flow cell withou