Table 2. Commonly Used Ion Selectivity Definitions in the Literature.

symbol	equation	description
Pji(184) or Sj190		Ji and Jj are the flux (in mol·m–2·s–1) of the target and competing ions, respectively. ci and cj (in mol/L) are the concentrations of the target and the competing ion on the diluate side, respectively.
Fji(188),a		Ji and Jj are the flux (in mol·m–2·s–1) of the target and competing ions, respectively, when the source phase contains equal concentrations of the target and the competing ions.
ρji183 or βj197		ci,0 and ci,f are initial and final concentrations of the target ion. cj,0 and cj,f are initial and final concentrations of the competing ion.
Rji(190)		Ri and Rj are the resistance (in Ω·cm2) of the target and the competing ion, respectively.

^aIn literature, there is no symbol used for this type of selectivity; here, we introduce F for matters of clarity.