Surface Characterization of Phenylpropanolamine Drug by Inverse Gas Chromatography

The surface thermodynamic properties can be used to understand the interactive potential of a drug surface with a solid or liquid excipient during its formulation and drug release process. The retention data were measured for n-alkanes and polar solutes at intervals of 5？K in the temperature range 318.15–333.15？K by Inverse Gas Chromatography (IGC) on the solid surface of phenylpropanolamine (PPA) drug. The retention data were used to evaluate the dispersive surface free energy, , and Lewis acid-base parameters, and , for the PPA drug. The values, , were decreasing linearly with increase of temperature and at 323.15？K the value was found to be ？mJ/m2. The specific components of enthalpy of adsorption of polar solutes have been applied to evaluate Lewis acid-base parameters. The and values were found to be and , respectively, which suggests that the PPA surface contains more basic sites and interact strongly in the acidic environment. 1. Introduction The surface energetics of a pharmaceutical solid will influence its interaction with another solid or liquid when it is in close contact. An interfacial energy will be developed at the interface when two such condensed systems interact. The magnitude of this interfacial energy depends on the individual surface energies of the two systems. The interfacial energy will influence several factors such as wetting and spreading of a liquid over a solid surface, binding of a film to a tablet, wet granulation, and dissolution and suspension formulation of a drug during processing [1–9]. Several techniques are available to measure surface energetics of a solid; however, the IGC method has been proved to be more effective and simple technique [10–15]. In the IGC method n-alkanes and polar probes are injected at infinite dilution on a column packed with pharmaceutical material. The surface free energy of a pharmaceutical solid is often divided into two components dispersive and specific. The dispersive surface energy is usually investigated by using the retention data of n-alkane solutes and the specific interaction ability of the surface has been studied using the data of polar solutes. The comparison of the retention property of the polar solutes with the n-alkanes will result in the evaluation of Lewis acidity, , and Lewis basicity, , parameters. The purpose of this paper is to determine the surface thermodynamic properties of PPA drug by IGC method. The dispersive surface free energy at four temperatures and Lewis acid-base parameters for the solid PPA surface has been reported. PPA is an important drug which can be