Antec Scientific DECADE II 171, User Manual, Page: 64 / 87

64 DECADE II user manual, ed. 11
Hydrodynamic and scanning voltammogram
A hydrodynamic voltammogram is constructed when the pure analyte is not
available and separation over an analytical column is required. Furthermore,
under real chromatographic conditions reliable information about the S/N
ratio is obtained
In case of metal working electrodes it is also advisable to use a
hydrodynamic voltammogram. On the metal working electrode an oxide layer
is formed which affects the electrochemical reaction and makes the
interpretation of a scanning voltammogram difficult.
Fig. 36. Hydrodynamic voltammogram of norepinephrine (A) at a glassy
carbon working electrode, and the current of the baseline (B). At E
1
the
electrochemical signal becomes diffusion limited.
An alternative for the chromatographic construction of an I/E relationship is
the application of scanning voltammetry. The working potential runs between
two pre-set values and the current is measured while the analyte is
continuously flushed through the flow cell.
As peak heights are used, the signal in Fig. 36, line A is only due to the
analyte. The signal in Fig. 37, line A is the sum of the analyte signal and the
background signal. Subtracting both lines in Fig. 37 results in a similar I/E
relationship as in Fig. 36, line A. It takes only a few minutes to construct a
scanning voltammogram. This is an advantage, especially when a number of
analytes have to be characterised. However, as the scan is obtained in flow
injection analysis (FIA, without analytical column), it is a prerequisite to have
the
pure analyte dissolved in buffer. Any contamination may lead to
artifacts . A blank scan of the buffer should be used to distinguish between
solvent peaks and analyte peaks.