Determining Entrapment Efficiency of Drug Formulations

The entrapment efficiency was determined by the ultrafiltration method [40 (link)] using a Centrisart tube with a molecular weight cut-off of 10 kDa (Sartorius, Gottingen, Germany). Centrifugation was performed on the device containing 2 mL of the sample in the donor chamber for 30 min at 6000 rpm to separate the unloaded DTX or CCM in the aqueous phase into the inner floater tube. The drug solution in both the recovery and donor chambers was collected and quantified using the HPLC method as outlined in our previous report [30 (link)]. The following equation was used to calculate the percentage of drug that was entrapped.
$$\mathrm{Entrapment} \mathrm{efficiency} (\%)=\frac{\mathrm{Winitial} - \mathrm{Wobtained} }{\mathrm{Winitial}} \times 100$$
where “ $\mathrm{Winitial}$ ” is the amount of drug loaded in the formulation, while “W_obtained” is the amount of unloaded drug in the aqueous phase of the formulation.