Liquid–Liquid Extraction from Frozen Aqueous Phases Enhances Efficiency with Reduced Volumes of Organic Solvent

Liquid–liquid extraction is widely employed for the separation and analysis of mixtures of compounds, both in the laboratory and in industry. Although a large volume of organic solvent is required to maximize extraction efficiency, the principles of sustainability and green chemistry dictate that the consumption of organic solvents should be minimized. This paper proposes a new liquid–liquid extraction method, realizing high extraction efficiencies with only a small volume of organic solvent. Since extraction efficiency is a function of the ratio of organic and aqueous solvent volumes, attaining high extraction efficiency usually requires a large volume of the organic phase. In general, it is difficult to increase this ratio by reducing the volume of the aqueous phase, except by heatingwhich damages, and potentially decomposes, the solutes. However, if the aqueous phase is frozen, a freeze-concentrated solution containing the solutes is formed; the volume of the freeze-concentrated solution can be controlled by altering the main solute concentration and temperature. This paper demonstrates the extraction of organic molecules and metal chelates by freezing the aqueous phase. In some cases, freezing reduces the volume of the organic phase to a twentieth of that required to achieve the same extraction ratio without freezing