Phase Diagram for the System Water–Dimethylsulphoxide

Abstract

IN 1959, Lovelock and Bishop¹ reported the protective action of dimethylsulphoxide (DMSO) in preventing freezing injury to living calls. The “cryoprotective” action of this substance, now in wide use² for the frozen preservation of various types of living cell, presumably resides in part in its ability to reduce the extent to which salts are concentrated when water is converted to ice. On the basis of this assumption Farrant^3,4 proposed and developed two procedures by which DMSO might be used to prevent altogether the concentration of the soluble electrolytes in tissues cooled to temperatures in the range −78° to −196° C. In the course of his studies, Farrant obtained preliminary data describing the phase equilibrium behaviour of the system water–DMSO, both in the absence and in the presence of small quantities of salts. In view of the current interest in the use of DMSO we undertook a more extensive determination of the phase equilibrium and non-equilibrium behaviour of solutions of this compound in water. These measurements form the subject of this communication. They indicate (1) that the system water–DMSO can, in all proportions, be crystallized completely, and (2) that, in certain conditions, a stable hydrate (DMSO.3H₂O) is formed.