Solvent · nonpolar
Iso-octane C8H18
Also: 2,2,4-trimethylpentane
Weak (nonpolar) mobile phase and sample diluent in normal-phase HPLC, often blended with a polar modifier; low-boiling GC solvent and injection diluent; liquid-liquid extraction solvent for nonpolar/lipid analytes (e.g. isooctane vs acetonitrile fat partitioning); UV-transparent spectroscopy solvent; primary reference standard for octane rating (defined as 100).
Compiled by Hemant RawatLast reviewed July 2026How we verify
Properties
- Formula
- C8H18
- CAS number
- 540-84-1
- UV cutoff
- 215 nm
- Snyder polarity index (P′)
- 0.1
- Selectivity group
- — (non-selective)
- Eluotropic strength ε° (silica)
- 0.01
- Boiling point
- 99.2 °C
- Viscosity (25 °C)
- 0.5 cP
- Refractive index (nD²⁰)
- 1.3915
- Density
- 0.692 g/mL
- Water miscibility
- immiscible
- USP <467> class
- not classified
Safety
- highly flammable liquid and vapor (flash point approx -12 C)
- aspiration hazard - may be fatal if swallowed and enters airways (H304)
- skin irritant / defatting (H315)
- may cause drowsiness or dizziness (H336)
- very toxic to aquatic life with long-lasting effects (H410)
- not a listed carcinogen; not a peroxide former
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 Iso-octane mixes with
Miscible with: 1-Propanol, 1,2-Dichloroethane, 1,4-Dioxane, 2-Propanol, Acetone, Benzene, Carbon tetrachloride, Chloroform, Cyclohexane, Dichloromethane, Diethyl ether, Ethanol, Ethyl acetate, Methyl ethyl ketone, Methyl isobutyl ketone, MTBE, n-Butanol, n-Butyl acetate, n-Heptane, n-Hexane, n-Pentane, Pyridine, tert-Butanol, Tetrahydrofuran, Toluene, Triethylamine.
Partially miscible with: Acetic acid, Methanol, N-Methylpyrrolidone, N,N-Dimethylacetamide, N,N-Dimethylformamide — mix only over a limited range.
Immiscible with: Acetonitrile, Dimethyl sulfoxide, Water — these form two layers.
Check any specific pair on the interactive miscibility chart.
Using Iso-octane in HPLC/GC
Weak (nonpolar) mobile phase and sample diluent in normal-phase HPLC, often blended with a polar modifier; low-boiling GC solvent and injection diluent; liquid-liquid extraction solvent for nonpolar/lipid analytes (e.g. isooctane vs acetonitrile fat partitioning); UV-transparent spectroscopy solvent; primary reference standard for octane rating (defined as 100).
Its Snyder polarity index is 0.1, and its UV cutoff of 215 nm is low enough for most 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.