ABSTRACT
Several methods have been reported for the preparation of multiple emulsions. The double emulsi cation technique is the most commonly employed method of preparation compared to the one-step technique, which is sometimes called the phase inversion method (Matsumuto et al., 1985). Some of the more recent methods of preparation include the membrane emulsi cation technique (Okochi and Nakano, 1997) and microchannel emulsi cation methods (Sugiura et al., 2004). The membrane method uses a microporous glass membrane with a particular pore size as the emulsifying tool. The microchannel method is a very novel approach of producing monodispersed multiple emulsions. Various formulation variables including the method of preparation, emulsi ers, lipophilic phase, phase volume ratio of various phases, temperature, and shear or agitation used during preparation can affect the stability of multiple emulsions (Florence and Whitehill, 1981; Matsumoto et al., 1976). The rheological properties of these emulsions are affected by the nature of the external phase, phase volume ratio, and particle size distribution of the dispersed phase (Jiao and Burgess, 2003; Khan et al., 2006). Various in vitro methods have been used for the quality assurance of multiple emulsions in pharmaceutical practice. These include macroscopic and microscopic examinations, entrapment ef ciency studies, rheological analysis, zeta potential measurements, phase separation, and in vitro drug release characteristics (Khan et al., 2006). The difference in the nuclear magnetic resonance signals of a water proton in simple emulsions versus multiple emulsions has been utilized as an analytical tool in quality control (Khopade and Jain, 2001).
