Evaluation of two fluorescent probes for the characterization of W/O/W emulsions

The aims of this work were to select the most convenient fluorescent probe for the characterization of the W/O/W emulsion and to propose a new technique in order to study the release mechanism from the W/O/W emulsion. For this purpose fluorescence was compared with the well established conductimetric measurements using MgSO4.7H(2)O as electrolyte. Two fluorescent molecules were evaluated: 5,(6)-carboxyfluorescein (5,(6)-CF) and 1,3,6,8, pyrene tetrasulfonic acid, tetrasodium salt (PTSA). After their introduction in the inner aqueous phase of the W/O/W emulsions; their stability (in aqueous solutions) to temperature and to light, their sensitivity at different pH conditions and to the presence of the constituents of the inner aqueous phase, their partition between the different phases of the emulsions and their influence on rheological properties of the emulsions were analysed. PTSA was finally selected as the most convenient probe due to its high stability at different conditions and its excellent yield of encapsulation. After the release studies, a satisfying correlation between HPLC fluorescence and conductimetry was obtained. Both techniques confirm that the release mechanism of the multiple emulsion is swelling-breakdown.