Theory and procedure on which Reilley curve is based are discussed; it defines the minimum pH for an effective metal titration with EDTA. This curve, widely reported in Analytical Chemistry textbooks, was originally presented in an implicit way by Reilley, who assumed a 106 conditional constant for 0.01 M metal concentration. We report here the conditional constants necessary for 99, 99.9 and 99.99 complex formation percentage at various analytical concentration. An updated Reilley plot is furthermore presented, which takes into consideration all formation constants at 20°C reported till 1998 for EDTA complexes
