BAS 100B/W - Page 74

10-6
Therefore, for a reversible process, i
p
is proportional to the concentration, C, and the
square root of the scan rate,
υ
1/2
.
As discussed above, there are many parameters that can affect the shape of the
CV
curve. Slow electron transfer kinetics can increase the separation of the peak
potentials (
∆
E
p
), and the rate constant for electron transfer can be calculated by
examining the variation of
∆
E
p
with scan rate. However, uncompensated resistance
between the working and reference electrodes can also increase
∆
E
p
. The effect of
uncompensated resistance can be lowered or eliminated using electronic iR
compensation (see
iR Compensation
under the
Control
menu).
Another application for
CV
is the study of the reactions of electrolyzed species.
These are generated on the forward scan, and their reactivity can be examined on the
reverse and subsequent scans. Qualitative estimates of reaction rates can be obtained
by varying the scan rates.
The simplicity and speed of
CV
means that it is often used as the first technique to
characterize a redox system, and it is a very powerful technique for qualitative
analysis of kinetics and mechanism. However, quantitative kinetic measurements
using
CV
generally require digital simulation, since there is no other way to separate
the effects of slow electron transfer and chemical reactivity.
The charging current that is present in
CV
and
LSV
limit their usefulness as
techniques for quantitative analysis. However,
LSV
is used as one of the techniques
for the detection of trace metals using stripping voltammetry. This is discussed in
more detail in section 10.6.
It is important to note that the potential wave form used for
CV
and
LSV
on the BAS
100B/W (and other digital instruments) is a staircase wave form, since it is
impossible to generate digitally a true linear wave form. There has been much
discussion on the equivalence of "digital staircase"
CV
and
LSV
and "analog"
CV
and
LSV
, and it has been shown that variation of the parameters used for the
"staircase" techniques can lead to significant differences. Theoretical studies have
shown that equivalence can only be guaranteed if the potential step height of the
staircase wave form is less than 0.3/n mV (where n = number of electrons
transferred). Therefore, for
Scan Rates
in mV/s, the potential wave form used on the
BAS 100B/W for
CV
and
LSV
is identical to a true analog linear wave form, since
the step height is 0.1 mV. However, for
Scan Rates
in V/s, the step height is 1.6 mV,
so small inequivalences may arise.
BAS has a considerable number CV Notes, together with articles and Capsules that
describe the applications of CV (the articles and capsules are listed below). These can
beobtained at no charge from BAS.