The applicability of field-flow fractionation (FFF) to the characterization of liposomes is discussed and theoretically described. Because of fundamental differences in their driving forces, sedimentation FFF and flow FFF measure different vesicle properties. Sedimentation FFF, although used previously to measure vesicle sizes and size distributions, is fundamentally a technique that measures the effective mass and mass distribution of particles. It is sensitive to small changes in the effective mass of either the biomembrane or its encapsulated load and thus is likely to be useful in characterizing such properties as drug loading, bimembrane volumes and areas, and distributions of these properties. Size characterization by sedimentation FFF can only be done by deducing size from effective mass. Flow FFF, by contrast, provides a direct measurement of vesicle size and size distribution. After demonstrating the high resolution and relative accuracy of size measurement of flow FFF by the separation of polystyrene latex standards, flow FFF was applied to two preparations of DSPC-DSPA liposomes that were sonicated under different temperature conditions. Fractograms and size distributions are reported as a function of sonication time. The rapid elimination of a large diameter tail to the distribution is shown to constitute a major mechanism for distribution narrowing. Finally, results are provided bearing on the reproducibility of size distribution measurements by flow FFF.
Bibliographical noteFunding Information:
Acknowledgements - This work was supported by Public Health Service Grant GM10851-35 from the National Institutes of Health. The authors acknowledge the advice of Dr Yonghee Kim of the Department of Pharmaceutics at the University of Utah and Dr Sabrina Hoffstetter-Kuhn of Ciba-Geigy (Base& Switzerland) on the preparation of liposomes.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry
- Pharmaceutical Science
- Drug Discovery
- Clinical Biochemistry