The Mode of Action of Sodium Hypochlorite in the Cleaning Process

Abstract

The action of sodium hypochlorite (NaOCl) solution in the cleaning of alumina (Al₂O₃) particles fouled with bovine serum albumin (BSA) or pectin was studied as a function of pH. The efficacy of NaOCl in the cleaning process was evaluated in the pH region where OH^- alone exerted no significant action on BSA or pectin removal. The efficiency and the rate of the removal of BSA or pectin increased with increasing available chlorine concentrations and pH. The pH dependence of the efficacy of NaOCl could be explained on the basis of the equilibrium between undissociated hypochiorous acid (HOCl) and dissociated hypochlorite ion (OCl^-). The efficacy of NaOCl in the removal of BSA or pectin depended on the concentration of OCl^-, but not on HOCl. Size-exclusion chromatographic analysis showed that BSA molecules were partially decomposed by the action of NaOCl, whereas no significant variation in the molecular weight of pectin molecules took place. The difference between the actions of OCl^- in the removal of BSA and pectin could probably be ascribed to the reactivity of OCl^- with their molecules. It could be concluded that the concentration of OCl^- was a major factor determining the actual NaOCI concentration required for an efficient cleaning treatment.