Hygroscopic Study of Glucose, Citric Acid, and Sorbitol Using an Electrodynamic Balance: Comparison with UNIFAC Predictions

balance (EDB). The mass fraction of solute (mfs), dee ned as the ratio of the dry solute mass to the solution mass, of the additives was measured as a function of relative humidity (RH) at equilibrium. Bulk measurements and literature data suggest that these three additives all crystallize at their respective saturation conditions. However, crystallization or deliquescence was not observed for the suspended particles of the three additives. They behave as nondeliquescentmaterialsandsorbanddesorbwaterreversibly.At RH = 5%,citricacidparticlesstillcontain » 8wt%residualwater, which corresponds to a stoichiometry of citric acid monohydrate. Glucose and sorbitol particles are essentially water-free. Universal FunctionalActivityCoefe cient (UNIFAC)modelpredictsthewater activities of glucose, citric acid, and sorbitol (expressed as mfs of the particles ) to within §16%, 24%, and 6% of those determined by the EDB, respectively.