In the mid-to-late 1990s, twelve principles of "green chemistry" were formulated for researchers working in the field. The main goal for Analytical Chemists was to reduce the consumption of dangerous organic solvents, to choose a direct method of analysis, to miniaturize and automate analytical procedures as well as to try to use new ecological extraction media.
Various innovative extraction procedures using environmentally friendly solvents are currently being developed. These solvents include deep eutectic solvents (DES) and natural deep eutectic solvents. DES is a mixture of quaternary ammonium salts with donor molecules such as amines, amides, alcohols, carboxylic acids, sugar or polyols. DES components are often biodegradable and non-toxic. Its physical properties can also be tuned by choosing their individual components and ratio. However, generally this eutectic mixture is characterized by simple preparation, low volatility at high temperature, selectivity, strong dissolving ability and adjustable polarity.
The unique physicochemical properties of deep eutectic solvents, combined with their compatibility with various chromatographic and spectroscopic techniques, make them suitable for various sample analyses. DESs have been successfully utilized in liquid-liquid (micro)extraction for both organic and inorganic analytes. Organic compounds such as pharmaceuticals, plant bioactive compounds, pesticides, dyes, polycyclic aromatic hydrocarbons, phthalates, parabens, and endocrine disrupting compounds, among others, have been efficiently separated and pre-concentrated using DESs. Notably, DESs have also found applications in speciation analysis of elements and determination of anions, although these remain limited.
The advantages of DESs in liquid-liquid extraction over classical organic solvents are numerous, including their simplicity of preparation and their environmentally-friendly reputation as "green solvents".
The benefits and possibilities of application of DES have been further observed in the review article prepared within the cooperation of dr. Kalyniukova of the Subprogramme 3. The article "Application of deep eutectic solvents in analytical sample pretreatment (update 2017–2022). Part A: Liquid phase microextraction" authored by V. Andruch, A. Kalyniukova, J. Płotka-Wasylka, et al. is available here and in the nearest future you can get acquainted with the continuation of this article in part B.