Overview
EN ISO 6974-3:2018 - Natural gas: Determination of composition and associated uncertainty by gas chromatography - Part 3: Precision and bias (ISO 6974-3:2018) defines the expected measurement precision and gives guidance for assessing bias when applying the gas chromatographic method configured in accordance with ISO 6974-1. Prepared by ISO/TC 193 and adopted by CEN, this part complements the analytical procedure by quantifying variability between competent laboratories and by describing how to evaluate systematic error (bias).
Key topics and technical requirements
- Precision metrics: Defines how precision is expressed for natural gas composition analysis - primarily repeatability (short-term, same conditions) and reproducibility (between laboratories/conditions).
- Reference precision values: Provides reference repeatability and reproducibility values derived from statistical evaluation of interlaboratory data (14 proficiency testing exercises organized from 2012–2014).
- Bias assessment: Gives guidance on estimating and interpreting measurement bias and laboratory bias, including how to compare test results to assigned or reference values.
- Principle and scope: Clarifies that the precision values apply to the gas chromatographic method set up per ISO 6974-1 and are intended for use by one or more competent laboratories.
- Terms, symbols and definitions: Standardizes terminology (e.g., measurement precision, error of measurement, repeatability standard deviation sr, reproducibility standard deviation sR).
- Proficiency testing data: Includes an informative annex on proficiency scheme data evaluation and the statistical basis for deriving precision estimates.
- Normative references: Cross-references relevant documents, notably ISO/IEC 17025 and ISO 5725-series for statistical methods.
Applications and users
This standard is essential for organizations involved in natural gas analysis and quality assurance:
- Analytical laboratories performing gas chromatography for natural gas composition and uncertainty estimation.
- Gas producers, suppliers and pipeline operators performing custody transfer, quality control, and regulatory compliance testing.
- Regulatory bodies and certification entities that require harmonized precision and bias assessment methods.
- Proficiency testing providers and interlaboratory comparison organizers using standardized evaluation methods.
Practical uses include method validation, reporting measurement uncertainty, evaluating laboratory performance, and supporting contractual or regulatory decisions where accurate natural gas composition data are required.
Related standards
- ISO 6974-1 (method setup for GC analysis of natural gas)
- ISO/IEC 17025 (laboratory competence)
- ISO 5725 (accuracy - trueness and precision of measurement methods)
- ISO 6974 series (other parts covering components and data handling)
Keywords: EN ISO 6974-3:2018, natural gas, gas chromatography, precision, bias, measurement uncertainty, repeatability, reproducibility, proficiency testing.
