We developed two models for the estimation of stability constants in dioxane-water mixtures of mono-complexes of lanthanides (La3+, Ce3+, Pr3+, and Nd3+) with carboxylic acids (ethanoic, propanoic, and butanoic). The first, linear model proved suitable for the prediction of logK(1) at low mass fractions of dioxane, w = 0-20% (r = 0.981, S.E. = 0.06), whereas the second, quadratic model, yielded better results at higher fractions, w = 40-60% (r = 0.980, S.E. = 0.10). (C) 2012 Elsevier B.V. All rights reserved.