SURFACE-ANALYSIS OF PHARMACEUTICAL POWDERS - X-RAY PHOTOELECTRON-SPECTROSCOPY (XPS) RELATED TO POWDER WETTABILITY

Selected barbiturate powders (barbitone, butobarbitone, phenobarbitone and pentobarbitone) have been investigated using XPS. Where possible, samples were studied in the powdered and compacted form. The results indicated that the entire molecule was exhibited in the surface of the samples, irrespective of whether the sample was free powder or a compact. Various published results relating to the wettability of these barbiturates are reported. There is very poor correlation between results obtained by different methods, and also between the surface analysis and the wettability data. The surface energies of powders are known to vary following different physical treatments. One process which is thought to alter contact angles is that of compaction (ironically an essential part of many contact angle measuring methods). The surface analysis results demonstrate that these changes in surface energies are not as a result of changes in the chemical composition of the surface. XPS does not provide information concerning the orientation of the molecules in the samples. The fact that all of the molecule is exhibited does not mean that the hydrophobic portion of each molecule will have the same hindrance towards interactions with water molecules. Finally, the need for further fundamental investigations of techniques for assessing contact angles is highlighted.