Measuring Drug Encapsulation Efficiency

To determine drug encapsulation efficiency, nanoemulsion formulation samples (1 mL) were added to Eppendorf centrifuge tubes, then subjected to ultracentrifugation (Beckman Optima L-80, Beckman, Brea, CA, USA) at 13,000 × g for 2 hrs to obtain a clear supernatant.21 (link) The supernatant solution (0.1 mL) was withdrawn and stored at 4 °C until analysis. The supernatant was diluted with a 1:1 (v/v, 2.9 mL) methanol:water mixture to determine RIF content, and %EE was calculated using the following equation (3):
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$${\rm{EE}}\left({\rm{\% }} \right){\rm{\ =\ }}\left({{{\rm{E}}_{\rm{2}}}{\rm{/}}{{\rm{E}}_{\rm{1}}}} \right){\rm{ \times 100}}$$
\end{document}where E₁ and E₂ were the total drug content added to the formulation and the total free amount of drug, respectively. Rifampicin content was analyzed using a UV-Vis spectrophotometer at 337 nm.