Bearing in mind, the change in mass will be the product of concentration and change in volume; thus, the change of mass of solute (dm) in plate (p) will be

                         dm = (X_m(p-1) - X_m(p))dV                               (3)

Now, as equilibrium is maintained in the plate (p) by definition, the mass (dm) will be distributed between the two phases, resulting in a solute concentration change of dX_m(p) in the mobile phase and dX_s(p) in the stationary phase_{. Then,}

                             d_m = v_sdX_s(p) + v_mdX_{m(p)                         (4)}

 Substituting for dX_s(p) from equation (2),

                              d_m = (v_m + Kv_s)dX_{m(p)                             (5)}