pH compartmented w/o/w multiple emulsion: a diffusion study

In order to develop w/o/w emulsions characterized by two separate aqueous p hases of different pH, a preliminary study was carried out to obtain a bett er insight into the possible diffusion processes taking place between an in ner acidic aqueous phase and an external phase of higher pH (pH approximate to6). In fact, such systems could be of great interest for pharmaceutical use. For this purpose, a model emulsion was formulated. The study of pH and conductivity showed that acidic species transport take place between the t wo aqueous compartments. The three main release mechanisms that might be re sponsible for this passage across the oil phase were investigated: breakdow n of oil globules, facilitated transport by surfactant micelles across the oil phase or by Fickian diffusion. It appears that this last mechanism was involved. In order to control this diffusion process, an alkaline species, octadecylamine was introduced in the oil phase. This compound could form an ion pair with the lactate ion at the interface of the external aqueous pha se and the oil phase, thus, limiting the acidification of the external aque ous phase. (C) 2001 Elsevier Science B.V. All rights reserved.