A general formulation for I-D multicomponent localized adsorption is presented, as well as a new mixing function that varies with only temperature and spreading pressure. An understanding of this mixing function completely determines the solution thermodynamics of the system. A closed-form expression for the adsorbed-phase excess Gibbs energy exhibiting an explicit dependence on the spreading pressure is thus obtained The empirical expression proposed in the literature for the adsorbed-phase excess Gibbs energy is found to be consistent with the exact solution obtained in one dimension. The new mixing function further suggests the possibility of considering a binary adsorbed solution as the adsorption of a pseudo adsorbate.