The use of isotope exchange was recently shown to have a potential in determining continuous series of elementary steps in surface reactions. This was demonstrated by analyzing oxidation reactions on oxides. The method is based on equilibrating the oxide in O-16(2) then exposing it to O-18(2) and determining the dependence of the rate of (OO)-O-18-O-16 molecule desorption on oxygen partial pressure and on optional acceptor doping of the oxide. The isotope O-18(2) can be applied as a step function or as a pulse. We here discuss an implicit assumption made concerning the reaction that governs the isotope desorption, discuss the integrated desorption measured after the termination of a pulse of O-18(2), extend the discussion to isotopes other than oxygen and in particular show how to cope with the mass effect when Using deuterium and hydrogen and finally discuss the relevance of isotope exchange experiments, where chemical equilibrium prevails, to analyzing electrocatalysis and heterogeneous catalysis in which significant gradients in the defect concentrations may arise. (C) 2016 Elsevier B.V. All rights reserved.