Overview
ISO 7941:1988 - "Commercial propane and butane - Analysis by gas chromatography" specifies a laboratory gas chromatographic method for the quantitative determination of hydrocarbons in liquefied petroleum gas (LPG). The method applies to commercial propane, commercial butane and their mixtures containing C2–C5 saturated and unsaturated hydrocarbons. It excludes components present at concentrations below 0.1% (m/m) and is not intended for on‑line chromatography.
Key topics and technical requirements
- Scope and limits
- Quantitative analysis of propane, butane and associated C2–C5 hydrocarbons.
- Components below 0.1% (m/m) are excluded.
- Not suitable for on‑line GC systems.
- Sampling and safety
- References ISO 4257 for LPG sampling procedures.
- Safety warnings for LPG handling: risk of cold burns, static discharge (earthing recommended) and specific precautions when using hydrogen carrier gas.
- Chromatographic principle
- Physical separation on packed columns with identification by reference mixtures or relative retention times.
- Quantitation by internal normalization with peak area correction factors.
- Recommended columns and stationary phases
- Examples in the standard: packed columns with di‑n‑butyl maleate + PP′‑oxy‑dipropionitrile or sebaconitrile (1,8‑dicyano‑octane) on Chromosorb P support.
- Typical column lengths and packings are specified (e.g., 8 m + 3 m combinations or 6 m alternatives).
- Detectors and sensitivity
- Acceptable detectors: flame ionization detector (FID) or thermal conductivity detector (TCD) (hot‑wire or thermistor types).
- System must reliably detect and quantify components at the 0.1% level with acceptable signal‑to‑noise and linearity.
- Injection and analysis parameters
- Liquid injection preferred: 0.5–1 µL; gaseous injection up to 0.5 mL.
- Oven, injection port and detector temperature ranges, resolution requirements between critical pairs (e.g., propane/propene, propene/isobutane) and conditioning procedures are provided.
Applications and who uses it
- Analytical chemistry and quality control laboratories analyzing LPG composition.
- LPG producers, distributors and regulators performing specification testing and batch verification.
- Instrument manufacturers and method developers validating packed‑column GC methods for hydrocarbon mixtures.
- Safety and compliance teams requiring standardized test methods for commercial propane and butane.
Related standards
- ISO 4257 - Liquefied Petroleum gases - Method of sampling.
- ISO 565 - Test sieves (relevant to packing particle size).
- Users should refer to the latest editions of referenced standards for up‑to‑date procedures.
Keywords: ISO 7941:1988, commercial propane and butane, LPG analysis, gas chromatography, FID, thermal conductivity detector, packed column, internal normalization.
