Improved HPLC determination of the Centella asiatica terpenes:: Analysis in a multiple emulsion, influence of the surfactants on the retention

High performance liquid chromatographic methods were established for the determination of the three terpenic compounds of Centella Asiatica. The samples were analyzed with a Spherisorb ODS-2 reversed phase column and detected at UV 206 mn. Regression equations were derived showing linear relationships (individual correlation coefficients ranged between 0.998-1.000). This quick and simple method has been used for evaluating the interaction of Centella Asiatica terpenes with surfactants. By comparing the elution volume of terpenes injected onto the surfactant-free column (V-e) with that of terpenes injected onto the surfactant-doped column (V), an association constant (K-a) for the terpene-surfactant complex was determined.