An investigation into the distribution of lecithins in nanosuspension systems using low frequency dielectric spectroscopy

Abstract

A range of nanosuspensions comprising a model drug (RMKP 22) with varying concentrations of Phospholipon 90 were prepared using high pressure homogenization and analyzed using low frequency dielectric spectroscopy as a novel means of characterizing the distribution of Phospholipon 90 within the suspensions. A corresponding range of aqueous Phospholipon 90 suspensions were also studied for the purpose of comparison. The dielectric responses were interpreted using a modification of the Maxwell–Wagner approach, whereby the systems were considered to comprise a high frequency response corresponding to the bulk layer serially connected to a lower frequency response corresponding to an electrode barrier layer. The low frequency responses of both the Phospholipon 90 dispersions and the nanosuspensions were found to be essentially independent of phospholipid concentration, indicating the presence of a barrier layer covering the electrode surfaces. In contrast, the high frequency (bulk) loss response was found to increase with Phospholipon 90 concentration for the surfactant suspensions while a maximum in response was seen with Phospholipon 90 concentration for the nanosuspensions; this behaviour was attributed to the presence of impurities within the phospholipids. Based on this investigation, a model is proposed with which the dielectric response may be related to the surface coverage of the suspended drug particles.