Leave-one-ion-out cross-validation for assisting in developing robust QSPR models of ionic liquids

•The leave-one-ion-out cross-validation (LOIO-CV) is proposed to evaluate the ILs-QSPR model.•Two f(T,P,I)-QSPR models are developed to predict density (ρ) and viscosity (η) under variable temperatures and pressures.•Strict rules for dividing the training/test set are employed.•The stability and predictability of the two models are fully evaluated.