Chemistry Reference
In-Depth Information
where
I
1
is the limiting-current of the plateau at -0.5 V vs. Ag|AgCl. This
current is counted twice, because
I
1
corresponds to the reduction of oxygen
to hydrogen peroxide with the exchange of two electrons. However, the
same oxygen reduction also contributes to the second plateau, but in this
case it is the reduction to water with exchange of four electrons. Therefore,
the contribution of
I
1
to the current
I
2
has to be counted twice.
I
2
is the
limiting-current at -1V vs. Ag|AgCl, corresponding to the sum of the reduc-
tion reactions of oxygen (Equation 3.8) and hydrogen peroxide (Equation
3.9).
To link
I
2
to the hydrogen peroxide concentration, first a calibration curve
was obtained by measuring
I
2
in a series of solutions with known hydrogen
peroxide concentrations and in the absence of dissolved oxygen (Fig. 3.7).
From this curve, it is possible to obtain the hydrogen peroxide concentra-
tion by measuring the experimental limiting-current,
I
2
, compensate it for
I
1
and calculate the hydrogen peroxide concentration using Equation 3.12:
[3.12]
c
=
k
I
hp
3
90
80
70
60
50
y = 1360.9x + 0.1692
R
2
= 0.9998
40
30
20
10
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Concentration (mol l
-1
)
3.7
Calibration plot of the reduction of hydrogen peroxide at a glassy-
carbon rotating-disc electrode in the absence of dissolved oxygen.
pH
=
5.2,
T
=
303 K,
E
=-
1V vs. Ag|AgCl and
N
=
1000 rpm. (From
Sensor system for simultaneous measurement of oxygen and
hydrogen peroxide concentration during glucose oxidase activity
in
Electroanalysis Journal
, 1999. Reprinted by permission of
Wiley-VCH)
