A new application for the Antoine equation in formulation development

Characterization of formulation components in pre-formulation and formulati on studies will be made easier if a rapid method to evaluate the evaporatio n characteristics of an ingredient in the formulation is developed. This st udy aims at providing a,simple and rapid thermogravimetric method for estim ating the vapor pressure characteristics using the Antoine equation as the analytical tool. The heat treatment for the majority of benzoic acid deriva tives follows zero-order rate processes that are in good correlation with t heir evaporation process. The optimum conditions for the rising temperature experiments were found when the heating rate was 10 degreesC/min in an atm osphere of dry nitrogen (100 ml/min). Methyl paraben was taken as the calib ration compound since its Antoine constants are reported in the literature, and its selected thermodynamic parameters were evaluated using the Langmui r equation. The coefficient of vaporization ((k) under bar) was determined to be 124 525 +/- 0.8, with units being reported in the S.I. system. The co rresponding vapor-pressure plots were obtained for the remaining compounds and their Antoine constants calculated. (C) 2001 Elsevier Science B.V. All rights reserved.