The solution-diffusion transport model equations with a correction for concentration polarisation (Eq. 8 and 9 from the main text) were fit to the experimentally inferred values of 𝐽 ! , 𝑅 @B' and 𝛥𝛱, where 𝛥𝛱 was calculated using Eq. 10 from the main text to correct for solvent non-ideality. The fit was obtained by arranging Eq. 8 and 9 as 𝛥𝛱 = 𝑓(𝐽 ! ) and 𝑅 @B' = 𝑓(𝐽 ! ) , and finding the values of A, B and k that minimize the RMSE sum between data and predicted values for 𝛥𝛱 and 𝑅 @B' for all measured 𝐽 ! . Simultaneous fitting of both equations was done using the minimize functionality from the python scipy.optimize package. The obtained best fit is shown in Figure . s -1 , and 𝑘 ,% =6.9×10 -6 m 3 m -2 s -1 . Figure shows the variation of 𝐽 ! with the effective transmembrane driving force. Figure shows 𝑅 @B' as a function of 𝐽 ! . Uncertainties in 𝑅 and 𝛥𝛱 result from the propagation of errors in 𝑐̅ ?,.@? and 𝑐̅ K(B),.@? . Errors in 𝐽 ! stem from the propagation of random errors in 𝑡 ̅ N .