The phase-shift method and correlation constants, that is, unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the behavior (-phi vs E) of the phase shift (90 degrees >= -phi >= 0 degrees) for the optimum intermediate frequency and that (theta vs E) of the fractional surface coverage (0 <= theta <= 1) of intermediates for sequential reactions, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On Pt-Ir (90:10% (by weight)) alloy in 0.1 M LiOH (H(2)O) and 0.1 M LiOH (D(2)O) solutions, the Frumkin and Temkin adsorption isotherms (theta vs E), equilibrium constants (K), interaction parameters (g), rates (r) of change of the standard Gibbs energies of hydroxide (OH) and hydroxide and deuteroxide (OH, OD) with theta, and standard Gibbs energies (Delta G(0)(0)) of OH and (OH, OD) are determined and compared using the phaseshift method and correlation constants. Depending on theta (0 <= theta 1), the value of K for OH is approximately 1.4 to 11.5 times greater than that for (OH, OD). The OD effect on the adsorption of (OH, OD) on the Pt-Ir alloy in 0.1 M LiOH (D(2)O) solution is not negligible, especially when E is high and theta approximate to 1. Both the values of K for OH and (OH, OD) decrease with increasing E and theta. A lateral repulsion (g > 0) interaction between the adsorbed OH or (OH, OD) species appears.