Chlorine is widely used in industry as a strong oxidizing agent. One of its most important features is that it can be used as a disinfectant in water treatment and purification. When it is used for disinfection, disinfection gets faster due to the rapid attack to microorganisms by its active chlorine species. Such chlorine is generated during the reaction of chlorine ion with ozone at the time of ozone disinfection of seawater.
Recently, ozone has often been used for water disinfection in swimming pools and aquariums that use seawater. When seawater undergoes ozone disinfection, ozone as a stronger oxidizing agent oxidizes chlorine ion in the seawater, thus generating free chlorine. However, too much consumption of ozone results in the higher amount of free chlorine, which is harmful to the fish and the human body.
The amount of free chlorine in various kinds of aqueous solutions can be determined by several methods including titration, spectrophotometry and electrochemical analysis. The quantification of free chlorine by electrochemical analysis is accepted as an economical and reliable method with high selectivity since it employs oxidation and reduction properties of free chlorine.
It is an innovative analysis that determines the amount of free chlorine by using the oxidation peak of the hydrogen generated by water analysis during the cyclic voltammetry (CV) with a bare platinum electrode with no addition of any supporting electrolyte to the seawater.
However, since the peak potential of the oxidation peak of the hydrogen generated through water electrolysis in CV of seawater using a bare platinum electrode ranges from -0.8 V to -0.9 V, it could be overlapped with the peaks of some components essentially coexisting in the sample. Furthermore, as platinum has excellent electrochemical characteristics, it has a defect of exhibiting the low selectivity for indirect determination of free chlorine.
Ko Kye Hak, a researcher at the Faculty of Chemical Engineering, has proposed a new possibility of indirect determination of free chlorine using a graphite-epoxy composite (GEC) electrode instead of Pt disk electrode by interpreting the relationship between the peak current of the oxidation peak for hydrogen generated through water electrolysis in CV and the amount of free chlorine.
According to the quantitative analysis, the sensitivity for the GEC electrode is one third of that for the bare platinum disk electrode, but better results can be obtained without any effect of interferences.
You can find more information in his paper “Indirect determination of free chlorine in seawater by cyclic voltammetry using graphite-epoxy composite electrode: Hydrogen adsorption capacity of graphite-epoxy composite is one-third of that of platinum” in “Sensing and Bio-Sensing Research” (SCI).
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