Stability of Weakly Acidic Hypochlorous Acid Solution with Microbicidal Activity

Current understanding of disinfectant stability is limited in the context of weakly acidic hypochlorous acid solutions. While prior research has shown that hypochlorous acid can exhibit antimicrobial effects, the factors influencing its stability remain unclear. No prior work had resolved how environmental conditions or chemical contaminants impact HOCl's longevity or activity. This uncertainty drove the need for a study focused on HOCl's stability under various conditions. Existing methods often overlook the influence of organic and inorganic compounds on HOCl degradation. The field lacks comprehensive data on how specific ions and organic molecules affect HOCl's microbicidal activity. This gap motivated the investigation into HOCl's behavior when exposed to common contaminants and environmental stressors. The study aimed to clarify how these factors influence both the chemical stability and functional performance of HOCl solutions.

The study aimed to evaluate the stability and antimicrobial effectiveness of a weakly acidic hypochlorous acid solution. Researchers focused on how environmental and chemical factors influence HOCl's degradation and activity. The primary problem addressed was the lack of clarity regarding HOCl's longevity in practical settings. By identifying degradation triggers, the study sought to inform better formulation and storage practices. The motivation stemmed from the need to optimize HOCl as a disinfectant in real-world applications. The researchers aimed to determine which conditions and contaminants most significantly reduce HOCl's stability and antimicrobial potency. This work was driven by the observation that HOCl solutions often lose effectiveness prematurely. The study's goal was to provide actionable insights for producing and preserving stable HOCl solutions.

The researchers prepared a 200 ppm HOCl solution with a pH of 6 and tested its stability under various conditions. They exposed the solution to ultraviolet light, sunlight, and elevated temperatures of 25°C or higher. The team also assessed the impact of contact with air on HOCl degradation. In addition, they introduced organic compounds such as proteins and carbohydrates into the solution. Inorganic ions like NO2−, SO3−, PO3−, Fe2+, Cu2+, and CuS were tested for their effects on HOCl stability. The microbicidal activity was measured against coliform bacteria and total viable cell counts. The study used controlled experiments to isolate each variable's influence on HOCl degradation. The results were analyzed to determine which factors most significantly reduced HOCl's antimicrobial effectiveness.

The study found that HOCl is highly unstable under ultraviolet light, sunlight, and temperatures above 25°C. Exposure to air also accelerated HOCl degradation. The presence of organic compounds like proteins and carbohydrates led to rapid HOCl consumption. Inorganic ions such as NO2−, SO3−, and Cu2+ similarly caused significant HOCl oxidation. These reactions reduced the solution's microbicidal activity against coliform bacteria. The total viable cell count also decreased when HOCl was exposed to these contaminants. The most stable HOCl solutions were those stored in pure water with minimal organic or inorganic content. Storing HOCl in dark, cool conditions below 10°C preserved its concentration and antimicrobial effectiveness.

The authors propose that HOCl solutions require careful formulation and storage to maintain stability and antimicrobial activity. They suggest that pure water with minimal organic and inorganic compounds is essential for HOCl longevity. Storing HOCl in dark and cool environments is recommended to prevent degradation. The study suggests that oxidation reactions with contaminants significantly reduce HOCl's effectiveness. The findings may guide the production of more stable HOCl solutions for practical use. The authors note that UV light, sunlight, and air exposure are major contributors to HOCl instability. They propose that reducing exposure to these factors can help preserve HOCl's antimicrobial properties. The study concludes that optimal conditions for HOCl stability involve low concentrations of contaminants and controlled storage environments.