Chemistry Reference
In-Depth Information
12.3.7 Conclusion
It can be concluded that the electrocatalytic detection of SO
2
is not simple
and is strongly dependent on pH. However, in this study it became clear
that the influence of the pH on the curves is not caused by variations in
carbon-fibre electrode properties, but purely by transformation and shift of
equilibrium conditions in solution. From this study, it can also be concluded
that weakly acidic or alkaline solutions should be used as electrolyte in SO
2
-
sensing applications. For an optimal detection limit, a buffer of pH = 4
should be used in combination with the reduction reaction of HSO
3
-
,the
main compound in solution related to SO
2
. In other cases, advantage should
be given to oxidation of SO
2
(and related compounds) to sulphate because
reduction causes formation of possible interfering and poisoning products.
Except for the pH range from 7.5-9, a detection limit of about 7.5 ± 0.1 ¥
10
-5
mol l
-1
is obtained for SO
2
or its related compounds (HSO
3
-
and SO
3
2
).
However, in a pH = 4 buffer, a detection limit of 4.0 ± 0.1 ¥ 10
-5
mol l
-1
is
obtained. The carbon fibres used in this study can also be used for detec-
tion of SO
2
-related compounds such as sodium dithionite and sulphite. Thus,
these fibres positioned in a flow-through cell can be an alternative for the
previously discussed wall-jet electrode configuration (Chapter 6), or the
results discussed in Chapter 7 can be adapted to a gold fibre positioned in
a flow-through cell.
12.4
Gold-fibre textile electrodes obtained through
chemical modification for the detection of Ce(IV)
during polymerisation reactions of bio-polymers
12.4.1 Introduction
During the past few decades, polymers have found wide applications, and
some synthetic polymers have become important components of the indus-
trial society
54,55
. As well as these synthetic polymers, there are also a large
number of naturally occurring polymers such as polysaccharides, polypep-
tides and proteins
56-59
. All polymerisation reactions, including both the 'syn-
thetic' and 'natural' polymerisations, can be divided into three main classes,
depending on the active species present in the reaction mixture: anionic,
cationic and radical polymerisations. In recent years, our research group has
been working on the development of synthetic cationic polymers that can
be used as non-viral vectors for gene therapy
60-62
. Recently, the synthesis
and evaluation of a series of polymers containing polyethyleneoxide (PEO)
blocks and PEO grafts was reported
62
. Both types of polymers were pre-
pared by radical chain reactions. The block co-polymers, containing a PEO
