Overview
EN ISO 6975:2005 (identical to ISO 6975:1997) defines an extended gas-chromatographic analysis method for natural gas. It specifies how to separate and quantify gases and hydrocarbon fractions using gas chromatography with thermal conductivity (TCD) and flame ionization detectors (FID). The standard supports detailed composition analysis (C1 to C5, C6+ fractions, inert gases and selected aromatics) required for calorific value, density, vapor‑phase equilibrium and feedstock evaluation.
Key topics and technical requirements
- Scope of analysis: Quantitative determination of helium, hydrogen, argon, oxygen, nitrogen, carbon dioxide, saturated hydrocarbons (C1–C5), C6+ hydrocarbon fractions and aromatics (e.g., benzene, toluene).
- Measurement capability: Typical measurement sensitivity ranges span low ppm levels (≈0.001% n/n) up to tens of percent for inerts (N2, CO2) and up to 100% for methane; hydrocarbons C1–C5 and C6+ are measured across their relevant concentration ranges.
- Analytical systems: Use of packed or capillary (open tubular) columns; detectors include TCD for main components and FID for hydrocarbons. Systems must support isothermal and/or temperature‑programmed operation.
- Identification and quantification: Retention index (linear retention index) is used for hydrocarbon identification; FID response is treated as proportional to carbon number for quantifying uncalibrated higher hydrocarbons.
- Calibration and traceability: Use of certified reference gas mixtures (CRMs) prepared gravimetrically or validated against primary standards (traceable per ISO 6142/ISO 14111). Control charts and response curves are required for ongoing quality control.
- Limitations: Not intended for oxygen compounds (water vapor, methanol, glycols), sulfur compounds, or samples containing measurable hydrocarbon condensate or dense phase gases. Identification above C10–C12 may be ambiguous - C6+ is often reported as grouped fractions.
Practical applications
- Gas composition reporting for transmission and distribution networks
- Calculation of thermophysical properties (calorific value, density)
- Assessment of gas quality for industrial consumers and chemical feedstock (aromatics)
- Vapor‑phase equilibrium and process modeling that require C6+ data
- Laboratory and on‑line monitoring where detailed compositional breakdown is required
Who should use this standard
- Natural gas analytical laboratories and gas quality testing facilities
- Pipeline operators and gas transmission companies
- Gas treatment and processing plants
- Gas metrology institutes and regulators ensuring traceable composition data
Related standards
Keywords: EN ISO 6975:2005, ISO 6975, natural gas analysis, extended analysis, gas chromatography, FID, TCD, certified reference gas mixtures, retention index, C6+ fraction.