64 DECADE user manual, edition 9
Construction of a hydrodynamic voltammogram
Before a hydrodynamic voltammogram can be obtained, the chromatographic
conditions should be optimised. 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 detector is stabilised in the DC mode at a high
potential. After stabilisation the background current is read from the
display of the detector (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 derivatisation 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. 27).
5. The peak heights and the background currents are plotted against the
working potential (Fig. 23).
6. The working potential which gives the best sensitivity is obtained by
plotting the signal-to-noise ratio against the working potential.
Construction of a scanning voltammogram
The scan mode is programmed in the ‘SCAN SET’ screen of the DECADE.
Depending on the data acquisition software that is used and the experimental
set-up, a full, half or continuous scan cycle can be chosen.
Fig. 28. Programming the scan mode in the 'SCAN SET' screen.
In the example of Fig. 24 and Fig. 29 a ‘half’ scan is used, sweeping the
potential from 0.2 V to 1.2 V. A full scan would include the reverse scan, i.e.
from 0.2 V to 1.2 V and back to 0.2 V. In the continuous mode the voltage is
swept up and down between both potentials.
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