3.7. Encapsulation Efficiency Determination

Protocol to calculate EE% and DL%

1) Measuring parameters
Initial amount of drug added: W initial
Amount of free/unencapsulated drug in the supernatant or filtrate: W free
Total weight of the final drug-loaded formulation: W formulation

2) Calculate encapsulated drug

The measuring parameters are usually based on the spectrophotometric method, where the absorbance values of the samples with a drug, and the supernatants after the centrifugation are measured. The amount (weight concentration) of free and encapsulated drug is evaluated from the calibration series, i.e., from the calibration curve. The most common approach is to measure the supernatant and calculate the “W free” from the calibration equation of the calibration curve. The encapsulated drug amount is then calculated by the difference:
W encapsulated = W initial - W free
This gives the amount of drug actually retained in the carrier.

3) Calculate EE%
Encapsulation efficiency is determined as follows:
EE% = (W encapsulated / W initial) * 100

4) Calculate DL%
Drug loading is calculated as follows:
DL% = (W encapsulated / W formulation) * 100

where W formulation is the total weight of the dried (nano)particles or final product, including both drug and carrier.

5) Example calculation

Suppose you begin with:

Initial drug = 10 mg
Free drug in the supernatant = 3 mg
Final dried formulation = 120 mg

Then:
W encapsulated = 10 - 3 = 7 mg
EE% = (7/10) * 100 = 70%
DL% = (7/120) * 100 = 5.83%
 

6) Experimental workflow
A typical workflow is:

Prepare the drug-loaded formulation.
Separate (nano)particles from the aqueous phase by centrifugation, filtration, or dialysis.
Measure the amount of free drug in the supernatant using UV-Vis, HPLC, fluorescence, or another validated assay.
Dry and weigh the final formulation.
Apply the formulas above.

7) Important practical notes

Make sure your assay for drug quantification is validated and linear in the concentration range you use.
If the formulation contains other substances that absorb at the same wavelength, you may need HPLC instead of UV-Vis.
If the final formulation contains residual solvent or moisture, the weight used for DL% may be inaccurate unless fully dried.