Solvent · polar protic
Acetic acid C2H4O2
Also: AcOH
Widely used as a volatile acidic mobile-phase modifier/additive in reversed-phase HPLC (typically 0.1-1%), to control mobile-phase pH (~3.5), suppress ionization of acidic analytes and improve peak shape; LC-MS-compatible volatile acid (though formic acid is more common). Rarely used as a bulk GC solvent because it is corrosive and causes peak tailing.
Compiled by Hemant RawatLast reviewed July 2026How we verify
Properties
- Formula
- C2H4O2
- CAS number
- 64-19-7
- UV cutoff
- 230 nm
- Snyder polarity index (P′)
- 6
- Selectivity group
- IV
- Eluotropic strength ε° (silica)
- —
- Boiling point
- 118.1 °C
- Viscosity (25 °C)
- 1.13 cP
- Refractive index (nD²⁰)
- 1.372
- Density
- 1.049 g/mL
- Water miscibility
- miscible
- USP <467> class
- Class 3
Safety
- flammable/combustible liquid (flash point ~39 C)
- corrosive - causes severe skin burns and eye damage
- harmful vapor / respiratory irritant
- not a carcinogen
- not a peroxide former
- not classified as reprotoxic
Reference only. Solvents can be flammable, toxic, or peroxide-forming. Always consult the Safety Data Sheet (SDS) and your lab's protocols before handling.
What Acetic acid mixes with
Miscible with: 1-Propanol, 1,2-Dichloroethane, 1,4-Dioxane, 2-Propanol, Acetone, Acetonitrile, Benzene, Carbon tetrachloride, Chloroform, Cyclohexane, Dichloromethane, Diethyl ether, Dimethyl sulfoxide, Ethanol, Ethyl acetate, Methanol, Methyl ethyl ketone, Methyl isobutyl ketone, MTBE, n-Butanol, n-Butyl acetate, n-Heptane, n-Hexane, N-Methylpyrrolidone, n-Pentane, N,N-Dimethylacetamide, N,N-Dimethylformamide, Pyridine, tert-Butanol, Tetrahydrofuran, Toluene, Triethylamine, Water.
Partially miscible with: Iso-octane — mix only over a limited range.
Check any specific pair on the interactive miscibility chart.
Using Acetic acid in HPLC/GC
Widely used as a volatile acidic mobile-phase modifier/additive in reversed-phase HPLC (typically 0.1-1%), to control mobile-phase pH (~3.5), suppress ionization of acidic analytes and improve peak shape; LC-MS-compatible volatile acid (though formic acid is more common). Rarely used as a bulk GC solvent because it is corrosive and causes peak tailing.
Its Snyder polarity index is 6 (selectivity group IV), and its UV cutoff of 230 nm limits low-wavelength UV detection.See what the polarity index means and the full UV cutoff table.
Sources
- University of Toronto (TRACES) — Burdick & Jackson — Solvent UV cutoff table (absorbance = 1 AU, 1 cm cell)
- Stenutz / L. R. Snyder — Solvent polarity index (P′) and selectivity groups
- NIST — Chemistry WebBook — thermophysical properties (BP, density, refractive index)
- PubChem (NIH/NLM) — Compound property records (physical constants, CAS, formula)
- USP <467> / ICH Q3C — Residual Solvents — solvent classification (Class 1/2/3)
Values are compiled from public references and were last verified July 2026. See ourmethodologyfor how we source and verify. Always confirm critical values against primary references and the SDS.
Related solvents
Other polar protic solvents to compare with Acetic acid.