| The sedimentation field-flow fractionation (sedFFF) system has been refined both from the system control point of view and with the aim of increasing the accuracy and reproducibility of the experimental measurements. Using polystyrene (PS) latex as an example, the analytical ultracentrifugation (AUC) technique has been compared with the sedFFF regarding their capabilities to size and to recover a given sample. It is found that AUC generally provides accurate size and quantity assignments. However, no fractions are collected, and correlation between size and other properties are therefore impossible. In sedFFF, particle sizes may be assigned accurately when the diameter is less than 400 nm. After applying the lift force correction, developed during this study, sedFFF can also be used to determine particle diameters up to 1 {dollar}mu{dollar}m. The refined sedFFF operation allows an accurate analysis of surface concentrations of adsorption of proteins, as confirmed by amino acid analysis.; The use of the combination of sedFFF and photon correlation spectroscopy (PCS) greatly increases the ability to characterize complex emulsions, which generally have unknown densities. Based on the relationship between elution volume and diameter, determined for each fraction by PCS, the sedFFF fractograms of emulsions may then be easily converted into the corresponding size/density distributions. When applied to Liposyn-II, an emulsion designed for administration as parenteral nutrition supplement for the evaluation of its stability under a variety of environmental conditions, it is found that electrolyte additives and organic solvent will generally destabilize the emulsion. However, incubation with human plasma does not affect its size distribution at all.; The investigation of the droplet size and density distributions of two commercial fat emulsions reveals that emulsion droplets of the same sizes may have different densities, suggesting possible variations in the emulsifier:oil ratio. Freeze fracture electron microscopic observation demonstrates that these droplets may have multilamellar structure and may also contain entrapped vesicles, proposed to be either micelles or inverse water-in-oil emulsions or both. The brief electrical FFF study has also indicated that the emulsion droplets, although of similar composition, may bear different surface charges. |
