ISO 11352:2012

Overview

ISO 11352:2012 - Water quality: Estimation of measurement uncertainty based on validation and quality control data - defines practical, top-down methods for estimating measurement uncertainty of chemical and physicochemical methods in single laboratories performing water analysis. The standard is intended for quantitative measurement procedures and uses validation data plus internal and external quality control (QC) results to quantify uncertainty. It aligns with the principles of ISO/IEC Guide 98-3 (GUM) but emphasizes an accessible, QC-driven approach for routine laboratory use.

Key Topics and Requirements

• Scope: Applies to single-laboratory estimation of measurement uncertainty for chemical and physicochemical water analyses; excludes qualitative procedures.
• Top-down approach: Relies on performance characteristics extracted from method validation and analytical quality control rather than a detailed bottom-up component analysis.
• Two main components:
  • Within-laboratory reproducibility (random error) - derived from validation and QC datasets.
  • Method and laboratory bias (systematic error) - estimated from reference materials, interlaboratory comparisons or recovery experiments.
• Combined and expanded uncertainty: The combined standard uncertainty is obtained by combining (quadratic sum) the components for reproducibility and bias. An approximate coverage factor of 2 is applied to produce an expanded uncertainty at roughly 95% confidence.
• Preparatory requirements: Analysts must specify the measurand, measurement procedure, field of application (matrices, concentration ranges), and whether uncertainty will be reported as absolute or relative.
• Data sources and tools: Uses validation data, internal QC charts (including range control charts), external proficiency testing results; Annexes provide normative guidance and examples.
• When to separate estimates: If uncertainty varies substantially by matrix or concentration range, estimate separately for each range/matrix.

Applications and Practical Value

• Provides a straightforward method for environmental and water testing laboratories to report measurement uncertainty with confidence using routine QC and validation data.
• Useful for laboratory managers, quality assurance personnel, analysts, and accreditation assessors who need defensible uncertainty estimates for compliance reporting, regulatory submissions, or accreditation (e.g., ISO/IEC 17025).
• Helps interpret routine water quality data by quantifying the combined effect of random variation and systematic bias, improving data comparability and decision-making.

Related Standards

• ISO/IEC Guide 98-3 (GUM) - principles for expressing uncertainty of measurement
• NEN 7779, Nordtest TR 537, Eurolab TR 1, QUAM - approaches that influenced ISO 11352:2012

Keywords: ISO 11352:2012, measurement uncertainty, water quality, validation data, quality control, within-laboratory reproducibility, method bias, combined standard uncertainty, expanded uncertainty.