Overview
ISO 6144:2003 - Gas analysis: Preparation of calibration gas mixtures - Static volumetric method specifies a rigorous, repeatable procedure for preparing calibration gas mixtures using a static volumetric technique. The standard covers preparation for binary mixtures (one calibration component in a complementary gas such as nitrogen or air) and multi-component mixtures, calculation of the volume fraction of each calibration component, and a full evaluation of the expanded uncertainty associated with the prepared mixture.
Key practical points in the standard:
- Typical concentration scope: about 10 ppb to 50 ppm (parts per billion to parts per million) for many calibration components.
- Guidance on apparatus selection, measurement steps, homogenization and conditioning of the gas-mixing chamber.
- A detailed method for computing uncertainty that includes apparatus, procedure and purity of parent gases.
Key topics and technical requirements
- Principle: inject known volumes (or masses/volumes of volatile liquids) of calibration components into a diluent gas inside a gas‑mixing chamber, homogenize and pressurize to a known value, then calculate volume fractions.
- Apparatus: requirements for a gas‑mixing chamber, vacuum pump, pressure/temperature gauges, pressure‑relief valves, outlet sampling line, motor‑driven mixer, and calibrated metering syringes for precise injections.
- Measurement of chamber volume: methods (liquid displacement, mass increase) and temperature corrections for accurate total volume determination.
- Chamber conditioning: evacuation and flushing to remove contaminants and surface adsorbates before preparation.
- Uncertainty evaluation: rigorous, comprehensive analysis of all contributors (syringe volume, reservoir pressures, parent gas purities, residual vacuum, adsorption/reactions, instrument calibrations). The standard notes that a relative expanded uncertainty of about ±1% (95% confidence) may be achievable under appropriate conditions.
- Informative annexes: examples of apparatus, syringe volume determination, uncertainty calculations and stability testing.
Applications and who uses it
ISO 6144:2003 is used by:
- National and industrial calibration laboratories preparing in‑house calibration gases
- Manufacturers of gas analyzers and environmental monitoring equipment
- Quality assurance teams in ambient air and emissions monitoring programs
- Metrology institutes and academic researchers working on gas standards
Typical applications include generating calibration mixtures for SO2, NOx, CO, hydrocarbons and other trace gas analytes used in instrument calibration and regulatory compliance.
Related standards
Keywords: ISO 6144:2003, calibration gas mixtures, static volumetric method, gas-mixing chamber, metering syringe, uncertainty evaluation, gas analysis standard.
