Chemistry Reference
In-Depth Information
Time (s)
0
500
1000
1500
2000
2500
3000
3500
0
1c
1b
1a
-5
3c
2c
2b
-10
-15
2a
3b
-20
-25
3a
-30
-35
12.16
Chronoamperometric current signals recorded as a function of
time at a gold-modified PPy-polyaramide woven textile
structure (
E
=
0.25 V vs. Ag|AgCl) positioned in a flow-through
cell with a continuous flow of (a) 0.5 mol l
-
1
, (b) 0.05 mol l
-
1
and
(c) 0.005 mol l
-
1
H
2
SO
4
containing (1) 3
¥
10
-
5
, (2) 1
¥
10
-
4
and
(3) 2
¥
10
-
4
mol l
-
1
Ce(IV).
because, during their preparation, an immediate precipitation of Ce(IV)
was observed. Comparison of the peak currents obtained at different pH
values (between 0 and 6) for a constant concentration of Ce(IV) revealed
that the peak signal is not dependent on pH. This depends on both the flow
rate of the H
2
SO
4
solution and the volume of the injected sample. For the
flow rate (2.36 ml min
-1
) used in this investigation, the maximum volume of
a solution of pH 6 that may be injected is 260 ml. Higher volumes did give
rise to pH-dependent signals. Smaller values resulted in smaller peaks,
which negatively influenced the precision and detection limit of the method.
For the optimal condition of injection volume and a flow rate of 2.36 ml
min
-1
, the relationship between peak current and Ce(IV) concentration is
given by Equation 12.21. A detection limit of about 1 ¥ 10
-7
mol l
-1
was
obtained.
I
=
k
c
[12.21]
()
p
2
Ce IV
where k
2
is 197 000 for the electrode configuration used, when
I
p
and the
concentration were obtained in microamperes and mol l
-1
, respectively.
12.4.5 Analytical and kinetic considerations
Finally, the method was applied to determine the Ce(IV) concentration
during the polymerisation of polyethyleneoxide. A mixture of linear
