https://doi.org/10.1351/goldbook.DT06932
The equilibrium relation between the concentration of a sample component in the stationary phase \(c_{\rm{S}}\), and in the mobile phase \(c_{\rm{M}}\), expressed as a function \(c_{\rm{S}}=f(c_{\rm{M}})\). In some versions of chromatography, a distribution isotherm can be seen as a partition isotherm, an adsorption isotherm, or a combination of these, depending on the mechanism of separation.
Note: The relation can be influenced also by concentrations of other sample components. \(c_{\rm{S}}\) and \(c_{\rm{M}}\) are usually expressed per unit volume of the phase; \(c_{\rm{S}}\) may also be expressed per mass of the dry solid phase or per unit surface area.
This definition supersedes an earlier definition of distribution isotherm.