Iodine and Disinfection: Theoretical Study on Mode of Action, Efficiency, Stability, and Analytical Aspects in the Aqueous System

Abstract

Although they have been in use for nearly 170 years, the mode of action of iodine‐based disinfectants is not yet clearly understood, as is manifested, for example, in diverging judgements about the relevance of the individual iodine species. Although studies based on calculated equilibrium concentrations in pure iodine solutions have already been done, there is a lack of knowledge about iodine solutions in the presence of additional iodide which would be of intrinsic importance for disinfection practice. Therefore, a re‐calculation was undertaken considering variations of this parameter in the pH range 0—14. The presented calculations concern fresh iodine solutions not affected by disproportionation (iodate formation) and provide information about the equilibrium concentrations of the species I‐, I2, I3‐, I5‐, I62, HOI, OI‐, HI2O‐, IO2‐, and H2OI+. Additional iodide and the pH value have a very pronounced influence on the individual equilibrium concentrations (several powers of ten); hence, conditions can be indicated where the number of species of virtual importance is drastically reduced. In the most common case with iodine in the presence of additional iodide at pH < 6, only I‐, I2, and I3‐ play a role. In the absence of additional iodide, at pH 8‐9 and at high dilution (c(I2) < 10‐5M), on the other hand, HOI accounts for over 90% of the oxidation capacity. At high iodide concentration (e.g. Lugol′s solution) the species I5‐ and I62‐ make up 8.2% of the oxidation capacity. The iodine cation H2OI+, frequently quoted as an active agent in disinfection, is without any relevance under the conditions occurring in practice, as are IO‐ and HI2O‐ which become important only at pH > 10. The stability problem (i.e. rate of iodate formation) arising at pH > 6 can be reduced to hypoiodous acid, as manifested in the simple rate law d[IO3‐]/dt = 0.25[HOI]3/[H+] which allows an estimation of stability under weakly alkaline conditions. The results of this study allow us to deduce general qualities of aqueous iodine solutions, such as reactivity, stability, and analytical aspects, and to estimate major disinfection‐orientated properties such as microbicidal activity, irritation, and incorporation effects. Though the calculations consider primarily preparations devoid of polymeric organic compounds capable of complexing iodine species, the results can be largely transferred to iodophoric preparations.

Pore architecture of the ORAI1 store-operated calcium channel

“…Reactions with aqueous iodine were similarly carried out by the addition of Lugol solution (Sigma) to the final total iodine concentration indicated. Concentrations of aqueous iodine, which consists of I − , I 2 , I 3 − , and other species in proportions that vary with dilution (40), are given as moles atomic iodine per liter. The actual concentrations of oxidizing species are lower.…”

Effects of depth on transport of 129I in crystalline rock

“…The evaluation includes three components: (1) iodine speciation, (2) iodine sorption on rock minerals, and (3) evolution of groundwater compositions. Palmer et al (1985), Lengyel et al (1993) and Gottardi (1999) modeled the iodine speciation as a function of pH. Palmer et al (1985) studied hydrolysis of I 2 to I-and IO 3 À experimentally at the temperature range between 3.8 and 209°C.…”

“…Based on the analysis for direct measurements of the kinetics of iodine hydrolysis at various temperatures by Eigen and Kustin (1962), and Palmer and van Eldik (1986), Lengyel et al (1993) considered overall iodine hydrolysis reactions between pH 2 and 7, and modeled speciation as a function of pH by using a consistent set of equilibrium constants. Gottardi (1999) investigated iodine speciation for various pH. Since disproportionation to iodate proceeds rather slowly, he only considered the fast reactions in speciation calculations.…”

Preparation, stability and antimicrobial activity of cationic cross-linked starch–iodine complexes

“…Iodophores are complexes of iodine and a solubilizing agent or carrier. In an aqueous iodophore solution, iodine is present in the form of different thermodynamically stable anionic iodine species and diatomic iodine [2]. The two most important iodophores used nowadays are polyvinylpyrrolidone-iodine (or povidone-iodine) (PVP-I) and cadexomer-iodine (CI).…”