Acetonitrile is a cornerstone polar aprotic solvent in biochemistry and analytical chemistry, valued for its low nucleophilicity, UV transparency, and strong elution strength for hydrophobic analytes in chromatographic systems. Its physicochemical properties make it particularly suitable for high-resolution analytical workflows requiring reproducibility and minimal background interference.

Chemical Properties

Acetonitrile (CH₃CN) adopts a linear molecular structure characterized by a C≡N triple bond, producing 180° bond angles and a dipole moment of 3.92 D due to the high electronegativity of nitrogen. It exhibits a boiling point of 81–82°C, a melting point of −45°C, and a density of 0.786 g/mL. With a dielectric constant of 37.5, it is fully miscible with water, alcohols, and chloroform while remaining resistant to proton donation.

High-performance liquid chromatography (HPLC) grade acetonitrile (>99.9%) minimizes trace contaminants such as ammonia or water (<0.03%), ensuring stable baselines and highly reproducible solvent gradients in analytical applications.

Biochemical Applications

In molecular biology and analytical biochemistry, acetonitrile is widely used in reversed-phase HPLC for the purification of peptides, oligonucleotides, and next-generation sequencing (NGS) libraries. Gradient systems ranging from 5–95% enable efficient separation of carbohydrates, lipids, and other biomolecules based on hydrophobicity.

It is also employed in metabolomics for the extraction of intracellular metabolites prior to mass spectrometry analysis, supporting pathway profiling and untargeted screening studies. In proteomics workflows, acetonitrile facilitates protein precipitation from cell lysates and complements acetone in sample preparation protocols.

For virology research and ELISA-based assays, low concentrations (10–20%) help maintain chromatographic gradient stability without denaturing antibodies, while offering superior UV transparency in the 190–210 nm range compared to methanol.