Comparison of different separative techniques in the quantitative determination of active compound enclosed in...

Synopsis The suitability of three different separative techniques, dialysis, gel filtration and centrifugation, for determining the percentage of active compound included (PAI) in liposomal systems was assessed. Two model compounds, glucose and vitamin E acetate were encapsulated in dipalmitoylphosphatidylcholine (DPPC), soybean lecithin (SL) and hydrogenated soybean lecithin (HSL) multilamellar vesicles (MLV). Vitamin E acetate PAI values from DPPC MLV liposomes obtained by dialysis, gel filtration and centrifugation, were compared with those determined by differential scanning calorimetry. Glucose PAI values from DPPC MLV liposomes, obtained using the same separative techniques, were compared with that calculated by taking into account the glucose content of the liposome internal aqueous phase on the basis of liposome mean size determined by light scattering. Vitamin E acetate and glucose PAI values from SL and HSL liposomes were compared with those obtained for DPPC liposomes. Dialysis proved suitable for PAI determination for both lipophilic and hydrophilic compounds, centrifugation was found to be suitable only for the determination of lipophilic compound PAI values while gel filtration using Sephadex G-25M proved inadequate for the determination of PAI values for both lipophilic and hydrophilic compounds in the experimental conditions used in this study.