The experimental set up did not support concentration measurements inside the filtration cell, such that the nopinone concentration of the feed solution could not be monitored. Instead, the change in nopinone concentration throughout the experiment was inferred from mass balances on the overall system. The mean bulk solute concentration of the membrane feed solution at the start of each sampling interval 𝑘, 𝑐̅ 9(&),:,8 !"#$" , was inferred from Eq. 2 -4, using the mean measured concentrations of all collected 5 ml permeate batches, and the known concentration of the feed bulk at the beginning of sampling interval 1. The average concentration of the feed bulk throughout each sampling interval, 𝑐̅ 9(&),:,8 , was then approximated as the log mean of the feed bulk concentrations at the start and end of each sampling interval 𝑘 (Eq. 5).