MOISTURIZING SUBSTANCES ENTRAPPED IN W O/W EMULSIONS - ANALYTICAL METHODOLOGY FOR FORMULATION, STABILITY AND RELEASE STUDIES/

The purpose of this paper was to prove the efficiency of suitable trac er incorporation in the aqueous inner phase for multiple emulsion stud ies. The use of dihydralazine as tracer allowed the evaluation of both the yield of preparation and the stability of eight multiple emulsion s. In these, concentrations of several components were optimized i.e. oil, lipophilic and hydrophilic emulsifiers, coemulsifier and viscosit y increasing agent. From entrapment data and droplet breakdown curves, calculated from the dihydralazine chromatographic data, one emulsion was selected to study the release of some encapsulated moisturizing so lutes such as urea, chitosan and polyethylene glycol. Dihydralazine pr oved of value to discriminate between the two mechanisms responsible f or the solute release i.e. the breakdown of the multiple droplets and the diffusion of the solute through the oil layer. Diffusion curves we re obtained from the levels of moisturizing substance in the outer aqu eous phase, corrected by the amounts liberated by the droplet breakdow n calculated through dihydralazine levels. The lipophilicity of the so lutes measured under conditions similar to those partitionning in the emulsions correlated with the diffusional route of solute transfer. Th us, the partition coefficient was an efficient parameter to predict th e importance and the rate of the diffusion.