Overview
EN 27941:1993 (identical to ISO 7941:1988) specifies a laboratory gas‑chromatographic method for the quantitative determination of hydrocarbons in liquefied petroleum gas (LPG)-primarily commercial propane, butane and their mixtures. The method excludes components present at concentrations below 0.1 % (m/m) and is intended for batch laboratory analysis (it does not apply to on‑line chromatography). The standard defines safety warnings, sampling guidance, instrumentation, column packings, detector options and calculation procedures for reporting component concentrations.
Key topics and technical requirements
- Scope: C2–C5 saturated and unsaturated hydrocarbons in LPG; detection limit 0.1 % (m/m).
- Safety: Handling LPG (frost burns), earthing of containers to prevent static, and precautions when using hydrogen carrier gas.
- Sampling: Follow ISO 4257 procedures for representative LPG sampling prior to GC analysis.
- Chromatograph setup:
- Carrier gases: hydrogen, helium or nitrogen (hydrogen requires extra safety checks).
- Injection: liquid sample valve (0.5–1 µL) preferred; gaseous loop (up to 0.5 mL) alternative.
- Columns: recommended packings include di‑n‑butyl maleate ± PP′‑oxy‑dipropionitrile or sebaconitrile; tubing ID 2–5 mm; specific column lengths indicated for propane vs butane analyses.
- Packing support: Chromosorb P (acid‑washed, 180–250 µm fraction) and defined stationary phase loadings.
- Oven and injector temperatures: guidance provided (e.g., injector ≈40 °C; column conditioning and operating temperatures specified per column type).
- Detectors: thermal conductivity (hot‑wire or thermistor) or flame ionization (FID). System sensitivity must reliably detect 0.1 % components with acceptable signal‑to‑noise and repeatability.
- Resolution and performance: specified chromatographic resolution criteria to separate critical pairs (e.g., propane/propene and propene/isobutane) and procedure for column conditioning.
- Calibration and calculation:
- Internal normalization using corrected peak areas (peak area × correction factor).
- Correction factors provided as guidance; laboratories may determine their own.
- FID mass‑based correction approach based on carbon/hydrogen content is described.
Practical applications
- Quality control of LPG production and formulation (propane/butane blends).
- Regulatory compliance testing and verification for safety and trade.
- Custody transfer and commercial verification where accurate hydrocarbon composition is required.
- Laboratory method standardization for petrochemical testing labs and independent testing houses.
Who should use this standard
- LPG producers, distributors and retailers
- Analytical and quality control laboratories performing GC analysis of gaseous fuels
- Regulatory agencies, certification bodies and customs laboratories
- Instrument manufacturers and method developers implementing LPG GC methods
Related standards
- ISO 7941:1988 (original International Standard)
- ISO 4257 (sampling of liquefied petroleum gases)
- ISO 565 (test sieve requirements referenced for packing support preparation)
Keywords: EN 27941:1993, ISO 7941:1988, LPG analysis, gas chromatography, propane butane, flame ionization detector, thermal conductivity detector, chromatographic columns, sampling, calibration.
