Низкотемпературное разделение и концентрирование в условиях образования гетерогенных систем (обзор)

Abstract

The review considers modern approaches used in the methods of separation and concentration of biologically\xa0active compounds under conditions of formation of heterogeneous systems at low temperatures.\xa0The factors that improve the efficiency of low-temperature liquid-liquid extraction, cryoconcentration, and\xa0extraction freezing are discussed. The scope and capabilities of subambient HPLC are shown. The possible\xa0mechanisms of physical and chemical separation processes that are implemented in low temperatures are\xa0considered.In the pharmaceutical and food industries, cryoconcentration of substances from aqueous (organicwater)\xa0solutions has received the greatest development from cryometods. The solutions are cooled until ice is\xa0formed from water and aqueous (aqueous-organic) solution. The concentration of solutes is observed in the\xa0liquid phase. The ice is separated from the liquid phase by centrifugation. The effectiveness of cryoconcentration\xa0is increased by repeatedly repeating the freezing of already concentrated solutions, due to the use of\xa0shaking and increasing the freezing rate.With the introduction of a hydrophilic organic solvent into a cooled heterogeneous ice-liquid system\xa0(for example acetonitrile) a concentration option, called extraction freezing or liquid-liquid extraction withpartition at low temperature, is implemented. This method turned out to be convenient in the sample preparation\xa0of a number of analytes in the analysis by the method of reversed-phase HPLC.When the temperature drops to -10 ÷ -20°C, the mixture of acetonitrile and water quickly forms a\xa0heterogeneous system with two liquid phases, without a phase of ice. The organic lipophilic components are\xa0concentrated in a phase enriched in acetonitrile in this case. Low-temperature liquid-liquid extraction using\xa0acetonitrile and its mixtures with other organic solvents is also applicable to sample preparation in the HPLC\xa0method. Subambient HPLC is most effective in the separation of cis-trans-isomers, tautomers, thermolabile\xa0substances. The review examines in detail the manifestations of heterogeneity at the nano-, micro- and macro-levels observed in the process of cooling water-organic mixtures. The conditions for the spinodal decomposition\xa0of the liquid phase adjacent to the crystallization front are discussed. The analogies in the mechanism\xa0of the redistribution of analytes in the conditions of extraction freezing and hydrophilic liquid chromatography are carried out.