Effect of storage temperature and heating on the concentration of available chlorine and pH of 2.5% sodium hypochlorite

Aim: This study investigates the amount of available chlorine and pH of sodium hypochlorite after dilution and the influence of storage temperature, heating, and aging. Materials and Methods: A 5.25% sodium hypochlorite solution was diluted to 2.5%, and free available chlorine (FAC) and pH were measured. This was labeled as the control group. The diluted solution was divided into four groups. The first and second groups were stored at 4°C and room temperature, respectively, and FAC and pH were measured at room temperature at intervals of 30 min, 1, 3, and 6 h. The third and fourth groups were stored at 4°C and room temperature, respectively. Samples were collected at intervals of 30 min, 1, 3, and 6 h after heating to 60°C–70°C, and FAC and pH were measured. An iodometric titration method was used for FAC estimation. pH was measured using a digital pH meter. Data obtained were statistically analyzed. Results: All groups showed depletion in FAC and decrease in pH over time. Available chlorine was utmost in Group III and least in Group II. No statistically significant difference in pH was recorded. Conclusions: Sodium hypochlorite at room temperature should be used within 3 h of dilution. Its shelf life can be enhanced by storing at 4°C. Heating the solution to 60°C–70°C before irrigation is more efficacious.