Thermal analysis of lipoic acid and evaluation of the compatibility with excipientes

Differential scanning calorimetry (DSC) was used as a screening technique for assessing the compatibility of lipoic acid with some currently employed cosmetic excipients. In the first phase of the study DSC was used as a tool to detect any interaction. Based on the DSC results alone, methyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butylated hydroxytoluene, non ionic self emulsifying wax, propylene glycol and acetylated lanolin were found to exhibit interaction with lipoic acid. Stressed binary mixtures (stored at 50 degrees C for 1 week) of lipoic acid and excipients were evaluated by HPLC. Binary mixtures were evaluated by IR spectroscopy.