Detection and quantification of diiodine during the electrooxidation of pharmaceuticals on a boron-doped diamond electrode (BDD)

Abstract

Oxidative species play a very important role in the degradation process of organic pollutants. However, their detection and quantification are often very complex. In this work, the aim is to determine qualitatively and quantitatively the iodine (I₂) generated in situ during an electrochemical process by the starch-poisoning test and by spectrophotometry, respectively. Thus, for quantification, a simple, linear, reliable and accurate technique with a detection limit of 0.0023 mM and a quantification limit of 0.007 mM was used. Preparative electrolysis of NaI leads to the in-situ generation of iodine characterized by a very rapid increase in the concentration of I₂ during the first 20 minutes of electrolysis followed by a quasi-constant evolution of the concentration of I₂ until 240 minutes. The degradation of metronidazole (MNZ) (0.1 g/L) in the presence of NaI (0.05M) in KClO₄ medium (0.1M) leads to the in-situ generation of I₂ with a maximum concentration reached (1702 mg/L) after 5 minutes of experiment. After this date, a rapid decrease of I₂ in the medium is observed, which reflects the participation of I₂ in the MNZ degradation process. The contribution is positive from I₂ and it allows to reach 100% of the chemical oxygen demand (∆(COD)) abatement rate against 83.48% in its absence. In addition, iodine is generated during the electrolysis of telebrix (TLX) (1g/L). The release of I₂ is evidenced by the end-of-electrolysis coloration of TLX being identical to that obtained during NaI electrolysis, by the maximum wavelength of the TLX samples being identical to that of I₂ and by the starch stain test being positive.