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.