Determination of the changes in surface energetics of cefditoren pivoxil as a consequence of processing induced disorder and equilibration to different relative humidities.

The change in surface energy of cefditoren pivoxil powder as a consequence of changes in crystallinity (caused by milling duration) was studied using inverse gas chromatography (IGC) under dry conditions. The surface of the powder became more basic with decreasing crystallinity. It was suggested by considering the results of IR spectra that this resulted from exposure of the carbonyl groups, which have electron donating nature, on the particle surface. There was a direct correlation between surface energy and the % amorphous content induced during milling, giving the opportunity to use IGC to quantify amorphous content for this material. Furthermore, the changes in the acidic and basic properties on the surface of amorphous cefditoren pivoxil powder were investigated using IGC under various relative humidities (RHs). The basic nature on the surface of amorphous cefditoren pivoxil decreased with increasing RH, with a dramatic fall between 0 and 10% RH, this was attributed to water preferentially shielding the exposed carbonyl groups from acidic polar probes. Since water molecules would be adsorbed to the most hydrophilic sites at initial RH increment, it seems reasonable to suppose that the most hydrophilic adsorption sites on the surface of amorphous cefditoren pivoxil are the exposed carbonyl groups.