Separation of external aqueous phase from o/w nanoemulsions

The aim of this study is to develop a simple, reliable, timesaving and cost-effective method for separation of the external aqueous phase from o/w nanoemulsions. The method is based on centrifugation through a hydrophilic membrane. Five o/w nanoemulsions (droplet size of 20-200nm) with radio-labeled C18 triglyceride were prepared. These nanoemulsions were placed in tubes with cellulose membranes (10-50K molecular weight cut-off) and centrifuged at 250-3000g for 5-15min. The filtrates were analyzed for the presence of lipid droplets and radioactivity. The applicability of this method was tested on FITC-dextran-loaded nanoemulsion (FITC-dextran was expected to be in the lipid droplets) and a blank nanoemulsion mixed with FITC-dextran (FITC-dextran was expected to be in the external aqueous phase). The results show that no droplets were detected in the filtrate. The radioactivity in the filtrate was in the range of 0.3-2.9%. The volume of the filtrate increased with increase in the membrane pore size, centrifugal force and time, and decrease in droplet size. There was 41.6±4.2% and 98.4±0.8% FITC-dextran in the aqueous phase of the FITC-dextran-loaded nanoemulsion and the blank nanoemulsion mixed with FITC-dextran, respectively. In conclusion, centrifugation with hydrophilic membrane is an efficient and convenient method for the separation of the external aqueous phase from o/w nanoemulsions with droplet sizes in the range of 20-200nm.