ISO 6974-6:2002

Overview

ISO 6974-6:2002 specifies a laboratory gas chromatographic method for the quantitative determination of helium, hydrogen, oxygen, nitrogen, carbon dioxide and C1–C8 hydrocarbons in natural gas using three capillary columns. The method produces compositional data with defined uncertainty that are used to calculate calorific value, relative density and Wobbe index. ISO 6974-6:2002 is to be used in conjunction with ISO 6974‑1 (guidelines) and ISO 6974‑2 (measuring‑system characteristics and data processing).

Key topics and technical requirements

• Analytical scope and mole-fraction ranges: Component-specific mole-fraction ranges are defined (examples: helium 0.002–0.5%, hydrogen 0.001–0.5%, methane 40–100%, nitrogen up to 40%, CO2 up to 10%). These ranges indicate where the stated precision applies, not the absolute detection limits.
• Three-capillary-column setup: Uses a PLOT precolumn, a molecular‑sieve PLOT column for permanent gases and methane, and a WCOT (thick-film) apolar column for C2–C8 hydrocarbons. Columns are installed across one or two gas chromatographs (dual-oven or separate instruments).
• Detection and optional methanizer:
  • Permanent gases and methane: thermal conductivity detector (TCD).
  • C2–C8 hydrocarbons: flame ionization detector (FID).
  • For natural gas substitutes, a methanizer can be used to convert CO and CO2 to CH4 for FID detection at low mole fractions (recommended when CO/CO2