Acetonitrile, the polarity chameleon

Abstract

Acetonitrile (CH 3 CN, ACN) is a relatively nontoxic, highly volatile and aprotic polar organic solvent. ACN plays a key role as an extraction and deproteinization medium for a variety of pre-purification and concentration techniques using liquid-liquid extraction, solid-phase extraction (SPE) or microextraction (SPME) protocols. In terms of polarity, acetonitrile shows a number of unexpected physicochemical properties that may strongly affect the final results of analytical protocols applied in detection and separation science. Strong hydrogen bonding and the creation of low-polar self-associated forms of acetonitrile affect a number of physical and chemical properties of acetonitrile-water mixtures. The relatively low polarity of pure ACN can easily be disrupted by the presence of a small amount of water, which is usually present in either the raw biological sample or the ACN itself. The phenomenon of acetonitrile-water phase splitting at subambient temperature provides a convenient way to deproteinize biological samples and to preconcentrate target analytes.