2.6. Encapsulation efficiency (EE) and drug loading content

In order to measure encapsulation efficiency (EE), centrifugal ultrafiltration was used to separate the free OPC in the SDEDDS (Fan, Liu, Huang, Li, & Xia, ²⁰¹⁴). At first, 0.5 g of solid OPC‐SDEDDS was added dispersedly into 9.0 g of deionized water, and note that, dispersion was placed in the upper chamber of centrifuged tube with an ultrafilter (30 kDa, Millipore) and spun at 13,225 g for 30 min at 4°C. The OPC in SDEDDS (total drug) and ultrafiltrate (free drug) was determined by UV‐visible spectrophotometer. EE was calculated from the Equation 3, and drug loading content was calculated from the Equation 4. All experiments were verified in triplicate.

where W (total) is the total amount drug in OPC‐SDEDDS, W (free) is the amount of unentrapped drug, and W (excipients) represents the weight of added excipients in the preparation stage.