Biology Reference
In-Depth Information
Table 11.1. Types of elimination functions
EVLS Function
Characteristics
Equation
f
(
I
)
EVLS Equations
I
d
=
0;
I
k
=
=−
.
+
.
E1
0
f
(
I
)
3
4142
I
1
/
2
3
4142
I
a
1
I
1
/
2
+
a
2
I
I
d
=
0;
I
c
=
=
.
−
.
E2
0
f
(
I
)
4
8284
I
1
/
2
2
4142
I
I
d
=
0;
I
k
=
=
.
−
.
E3
0
f
(
I
)
3
4142
I
1
/
2
2
4142
I
I
d
=
0;
I
k
=
=−
.
+
.
E4
0;
f
(
I
)
11
657
I
1
/
2
17
485
I
I
c
=
−
.
0
5
8284
I
2
E5
I
d
=
0;
I
k
=
0;
a
1
I
1
/
2
+
a
2
I
f
(
I
)
=
6
.
8284
I
1
/
2
−
8
.
2426
I
I
c
=
0
+
a
3
I
2
+
2
.
4142
I
2
E6
I
d
=
0;
I
k
=
0;
f
(
I
)
=
4
.
8284
I
1
/
2
−
8
.
2426
I
I
c
=
0
+
3
.
4142
I
2
I
d
,
I
k
,and
I
c
are the diffusion, kinetic, and charging currents, respectively;
a
1
,
a
2
,and
a
3
are the
elimination coe
cients; and
I
1
,
I
2
,
and
I
3
are the total currents measured at three different scan
rates (
v
1
,
v
2
=
v
ref
and
v
3
).
Generally,
(i) EVLS functions can be set up for the different selected ratios
of scan rates. Then the new coe
cients
a
1
,
a
2
for E1, E2, E3 or
a
1
,
a
2
,
a
3
forE4, E5, E6EVLS functionsmustbe calculated [22].
(ii) The elimination procedure is not limited to the number of
particular currents. It can choose currents with different
dependences on scan rate and calculate the corresponding
elimination functions.
When the above two conditions are not fulfilled, the elimination
function obtained from the experimental voltammograms does not
correspond to the theoretical elimination function, and usually a
distortion of elimination curves may be observed. This distortion
can be used for the electroanalytical determination of some
depolarizators.Alargeincreaseinthesensitivityandresolutionwas
found in the case of the simultaneous elimination of charging and
kinetic currents (
I
c
,
I
k
), while conserving the diffusion current (
I
d
)
— the EVLS function E4 (Table 11.1). According to the behavior of
electroactive species, there are two types of transformation of
I
-
E
curves for an irreversible redox process:
(a) The transport of the electroactive species to the electrode is
controlled only by diffusion and in comparison to the measured
