Theoretical Prediction of the Water Activity of Standard Saturated Salt Solutions at Various Temperatures

A theoretical approach was used to predict the water activity (a w ) at 15°C and 35°C of selected saturated salt solutions used as standards in the range of microbial growth (∼0.57–0.97). For this purpose a rigorous thermodynamic model to predict osmotic coefficient was used. The results agreed very well with experimental measurements at 15°C and 35°C for most salts studied, which included NaBr, NaCl, (NH 4 ) 2 SO 4 , KCl, BaCl 2 , and K 2 SO 4 . For KNO 3 the agreement at the higher temperature was somewhat less satisfactory and the reasons for this behavior are discussed.