Abstract
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, γSd, and Lewis acid-base parameters, Ka and Kb, for the PPA drug. The values, γSd, were decreasing linearly with increase of temperature and at 323.15 K the value was found to be 26.01±0.40 mJ/m2. The specific components of enthalpy of adsorption of polar solutes have been applied to evaluate Lewis acid-base parameters. The Ka and Kb values were found to be 0.451±0.033 and 0.824±0.622, respectively, which suggests that the PPA surface contains more basic sites and interact strongly in the acidic environment.
Highlights
The surface energetics of a pharmaceutical solid will influence its interaction with another solid or liquid when it is in close contact
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 RT ln VN values are maximum at 323.15 K and decrease with increase of temperature in the range 323.15 to 333.15 K
Summary
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 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]. 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, Ka, and Lewis basicity, Kb, parameters
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