Chemistry Reference
In-Depth Information
At the beginning of this research, one of the aims was to develop a hydro-
gen peroxide sensor that would be useful in the complete pH area. When,
after the preliminary study, the glassy-carbon electrode was chosen for
further research but was limited for pH values in the envisaged high hydro-
gen peroxide concentration range, several attempts were made to use the
sensor system also in the lower pH area. Modifying the pre-treatment
method of the glassy-carbon electrode, adjusting the electrode configura-
tion and even investigating other electrode materials did not lead to a solu-
tion to the problem. When research is limited to the vitreous-carbon
electrode, it appears in the oxidation reaction mechanism on which the
sensor is based that a minimal concentration of hydroxyl ions is required.
Inevitably, it has to be concluded that the developed hydrogen peroxide
sensor cannot be adjusted to mediums with pH < 10.5 in combination with
the detection of high hydrogen peroxide concentrations.
Hence, other strategies were considered, e.g. a system where the sensor
is in permanent contact with an alkaline solution, which is separated from
the measurement solution by means of a membrane which sufficiently con-
ducts hydrogen peroxide. In such configurations, the fast response time and
advantages of this system obviously disappear. In general, this strategy boils
down to influencing the medium in which the measurements take place
instead of adjusting the sensor system itself to the medium. A possible
mechanism for achieving this strategy in practice is the so-called FIA (flow-
injection analysis) system. For further research, this method was preferred
because the advantage of the short response time was not lost. This study
is more exploratory than exhaustive and should be considered as a pre-
research investigation, aiming at figuring out whether the system qualifies
for further research.
FIA systems are used to investigate the kinetics of homogeneous chem-
ical reactions and for the analytical determination of many components by
means of spectrophotometric detection, amongst other applications. In the
latter method, a certain concentration of reagent (component forming a
coloured complex with the component to be determined) is added (injec-
tion), to a constant liquid flow of the solution in which the component to
be determined is situated (flow). The resulting solution subsequently passes
a reaction chamber, after which detection occurs by means of a spec-
trophotometer (analysis).
The aimed use of the FIA principle in the hydrogen peroxide sensor
system is similar. More specifically, the aim of this part of the research was
to verify whether the following approach could lead to the desired result.
A constant flow of a bleaching solution (flow) is mixed with a constant flow
of a solution with a known sodium hydroxide concentration (injection). This
concentration depends on the final pH of the process solution to be estab-
lished and is chosen in such a way that, after homogenising the two liquid
