The exact determination of supersaturation is essential for the studies of crystal growth processes in solutions. Due to peculiarities in the solubility of LiIO3, the refractive index of the solution is chosen as a measure of the supersaturation instead of undercooling. The experimental setup is based on a refractometer and a special setup to create supersaturation in the cuvette by means of successive evaporation of small amounts of solvent. The refractive index is measured at different solution concentrations and pH and the data are correlated as dependences of concentration and pH on the refractive index. The accuracy of the method and the adequacy of the model are discussed. (C) 2009 Elsevier B.V. All rights reserved.