Chemistry Reference
In-Depth Information
concentration, are identical, and therefore reference is made to section 2.3
for a more quantitative approach.
2.6.3
Potential step voltammetry
In potential step voltammetry, a DC potential window is covered by a DC
ramp (linearly increasing applied DC potential) with discrete and symmet-
rical pulses superponated to this ramp. As an alternative, the pulse ampli-
tude can increase with each pulse, superponated on a constant DC offset.
Methods where pulses are involved superponated on a DC signal are gen-
erally called potential step methods.
Normal pulse voltammetry
In normal pulse voltammetry
68
, rectangular potential pulses with increasing
amplitude
E
p
and constant pulse time t (10-100 ms) are superponated at a
constant DC offset
E
b
(Fig. 2.10).
E
b
is equal to a potential smaller than the
potential where the oxidation or reduction of the analyte starts to occur.
This offset can be situated in the background current region or in a limit-
ing-current region of a preceding oxidation/reduction reaction. The ampli-
tude of the pulses increases with constant time intervals (e.g. 0.5 s) with a
value D
E
.The current signal is measured at the end of the applied poten-
tial pulse, because under this condition the capacitive current is very small
compared with the Faraday response (Fig. 2.11). It may also be clear from
Fig. 2.11 that this effect depends on the pulse time, t.From Fig. 2.10, it can
Time (s)
2.10
Variation profile of the applied potential in normal pulse
voltammetry.
