Hygroscopic properties of a soluble crystalline solid are determined by the water activity of the saturated solution that is present on the crystal surface of the substance. If the substance contains impurities, then they are also found in the saturated solution and affect the solution’s water activity and, consequently, the hygroscopic properties of the substance. The isopiestic method is used to determine water activities of solutions and, thus, is a universal and accurate technique for examining the hygroscopic properties of substances. This review paper considers the specific requirements for the isopiestic method when used to study the hygroscopicity of substances. Additionally, it provides recommendations with regard to the device and appropriate methods for the processing and presentation of research results. The effect of heterogeneous soluble impurities on the hygroscopic properties of solids was studied. It is demonstrated that isopiestic investigations of concentrated and saturated solutions can be applied to study the hygroscopic properties of pure solids, and to evaluate the effect of impurities on the hygroscopic properties of substances.
ASJC Scopus subject areas
- Molecular Biology
- Physical and Theoretical Chemistry