This article deals with acetonitrile physico-chemical properties and its mixtures with water. It covers the information about isotherms of such parameters of the acetonitrile-water binary system as density, viscosity, permeation coefficient, refraction index, optic density, a boiling point isobar. Authors suggest a generalized criterion of acetonitrile polarity. The article also discusses means of polarity assessment and eluotropic strength of mobile phases on the basis of acetonitrile mixtures with water with application of generalized criteria. Special attention is paid to the options of acetonitrile application in various extraction methods of chromatographic sample preparation. The article also reveals advantages and problems of acetonitrile application as a mobile phase modifying agent in the HPLC reversed-phase and as a hydrophilic extra-agent in liquid-liquid extraction.

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