Application of Hildebrand Solubility Parameter for Selection of Organic Solvents in Dispersive Liquid Microextraction of Benzophenones

Background. Proper selection of organic solvents during extraction and microextraction is critical for quantitative recovery of analytes. The purpose of our work was to use the Hildebrand solubility parameter to select optimal extraction solvents and phases in the dispersive liquid microextraction of benzophenones. Methods. The paper uses literature data and calculated the Hildebrand solubility parameter values for a number of benzophenones and their acetylated derivatives, organic solvents and their mixtures. Organochlorine solvents methylene chloride, chloroform, tetrachloromethane, aprotic polar solvents acetone, acetonitrile were studied. The paper uses the preliminary results of the study of dispersion microextraction of benzophenones: optimized parameters, composition of extraction phases, extraction rates. Results. From the above-mentioned dependencies of the values of the extraction recovery of benzophenones on the difference in the solubility parameter of analytes and extraction solvents/extraction phases, it is concluded that the similar values of the solubility parameters of benzophenones and extraction solvents/phases indicate a high affinity between them and a high efficiency of using such solvents in dispersion liquid microextraction. The criterion for optimal selection of the extraction solvent/phase is the difference between the solubility parameter of the analyte and the extraction solvent/phase not more than 4,0. It is also shown in the work that similar values of the difference in solubility parameters between the extraction and dispersion solvents indicate the possibility of interchanging some extraction and dispersion solvents with others during microextraction. Conclusions. High recovery rates (60 to 96 %) of a number of acetylated and non-acetylated benzophenones, namely benzophenone, 2-hydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,4-dihydroxybenzophenone, confirm the feasibility of using the Hildebrand solubility parameter to optimize dispersion liquid microextraction. The Hildebrand solubility parameter is impractical for polar compounds that form hydrogen bonds with a solvent, for example diphenylmethanol. The obtained parameter values do not correlate with the degree of extraction of the analyte. It is also inappropriate to use the Hildebrand parameter to select optimal polar protic solvents if their content in the extraction phase is more than 1 %.