Phase diagram for the mixtures of ibuprofen and stearic acid

The binary mixtures of ibuprofen and stearic acid have been tested on the DSC at a heating rate of 5 degreesC min(-1). All temperatures reported here are for endothermic peak temperatures. The heating curves are employed to construct a phase diagram. The resultant phase diagram shows the existence of a compound formed between the two materials and is essentially two simple eutectic systems compressed into one equilibrium diagram. The component in excess melts at a lower temperature than its single entity. There are two eutectic melting points at 42% ibuprofen and 65% ibuprofen. It would seem probable that the "condensed phase compound" has the formula AB(2), where A is stearic acid (C18H36O2) and B is ibuprofen (C13H18O2) A relationship between the enthalpy of melting (DeltaH(m)) and %composition is found. However, the overlapped endothermic peaks pose difficulty in peak integration resulting in a deviation from a typical plot. DSC is a fast, useful, and reliable analytical tool to detect and investigate the eutectic compound in this study. (C) 2001 Elsevier Science B.V. All rights reserved.