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Brazilian Dental Journal

Print version ISSN 0103-6440On-line version ISSN 1806-4760

Abstract

NICOLETTI, Maria Aparecida; SIQUEIRA, Evandro Luiz; BOMBANA, Antonio Carlos  and  OLIVEIRA, Gabriella Guimarães de. Shelf-life of a 2.5% sodium hypochlorite solution as determined by arrhenius equation. Braz. Dent. J. [online]. 2009, vol.20, n.1, pp.27-31. ISSN 0103-6440.  http://dx.doi.org/10.1590/S0103-64402009000100004.

Accelerated stability tests are indicated to assess, within a short time, the degree of chemical degradation that may affect an active substance, either alone or in a formula, under normal storage conditions. This method is based on increased stress conditions to accelerate the rate of chemical degradation. Based on the equation of the straight line obtained as a function of the reaction order (at 50 and 70 ºC) and using Arrhenius equation, the speed of the reaction was calculated for the temperature of 20 ºC (normal storage conditions). This model of accelerated stability test makes it possible to predict the chemical stability of any active substance at any given moment, as long as the method to quantify the chemical substance is available. As an example of the applicability of Arrhenius equation in accelerated stability tests, a 2.5% sodium hypochlorite solution was analyzed due to its chemical instability. Iodometric titration was used to quantify free residual chlorine in the solutions. Based on data obtained keeping this solution at 50 and 70 ºC, using Arrhenius equation and considering 2.0% of free residual chlorine as the minimum acceptable threshold, the shelf-life was equal to 166 days at 20 ºC. This model, however, makes it possible to calculate shelf-life at any other given temperature.

Keywords : accelerated stability test; sodium hypochlorite solution; shelf-life; kinetics; chemical stability; irrigation solution.

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