Channel electrode waveshape analysis is employed to determine the rate of complexation of the radical anion of chloranil, with Mg2+ or Ba2+ ions in acetonitrile solution. The presence of less than stoichiometric amounts of M2+ results in a voltammetric wave for the reduction of chloranil which is split into two regions. At less negative potentials, the Nernstian equilibrium of chloranil and its radical anion is perturbed by the following reaction, resulting in current flowing at a more positive potential than with chloranil itself. At more negative potentials, the current-voltage response reverts towards that expected for chloranil alone once the supply of metal ion is exhausted. Analysis of the full waveshape is shown to be a sensitive method for the quantification of the complexation kinetics.