https://doi.org/10.1351/goldbook.S05582
The @[email protected] \(D_{i}^{*}\) of species \(i\) in the absence of a @[email protected] @[email protected] It is related to the @[email protected] \(D_{i}\) by \[D_{i}^{*}=D_{i}\ \frac{\partial (\ln c_{i})}{\partial \ln a_{i}}\] where \(a_{i}\) is the activity of \(i\) in the solution, and \(c_{i}\) is the concentration of \(i\). If an @[email protected] species (\(i^{*}\)) is used to study @[email protected], the @[email protected] @[email protected], \(D_{i}^{*}\), is practically identical to the [email protected]@ provided that the @[email protected] is sufficiently small.