Acetic acid is a weak organic acid widely used in biochemical and molecular biology laboratories. It plays a fundamental role as a pH modulator, protein precipitating agent, and analytical reagent in nucleic acid and lipid studies. Its biocompatibility, volatility, and miscibility with aqueous solutions make it particularly suitable for protocols requiring precise chemical control during sample preparation and biochemical analyses.

Chemical Properties

Acetic acid (CH₃COOH) is the simplest carboxylic acid after formic acid. Its molecular structure contains a planar carboxyl functional group and exhibits a pKa of approximately 4.76, allowing partial dissociation in aqueous solutions (a 1 M solution typically has a pH of ~2.4). It is a colorless liquid with a density of approximately 1.049 g/mL, a boiling point of 118°C, and a melting point of 16.6°C. Acetic acid is fully miscible with water, ethanol, and glycerol, and it presents a characteristic pungent odor reminiscent of vinegar. In non-polar solvents, it can form hydrogen-bonded dimers, a property that influences its physicochemical behavior in organic media.

Biochemical Applications

In molecular biology workflows, 0.1–2% glacial acetic acid is frequently used to stop enzymatic reactions such as those involved in RT-PCR workflows or to precipitate chromatin-associated proteins and nucleic acids. Concentrations of 10–20% are commonly applied to fix proteins within polyacrylamide gels (PAGE), preserving band integrity during electrophoretic analysis. In lipid biochemistry, derivatives such as acetic anhydride are used for methylation reactions, while acetate metabolites can be quantified in metabolic pathway studies using techniques such as high-performance liquid chromatography (HPLC). In immunoassays, acetic acid contributes to the preparation of acetate buffer systems (pH 4.5–5.5), which help maintain optimal antibody–antigen interactions during analytical procedures.