ISO 11843-6:2025

Overview

ISO 11843-6:2025 - Capability of detection, Part 6 - defines a statistical methodology for determining the critical value and the minimum detectable value (MDV) when both signal and background follow a Poisson distribution. The standard uses the conventional normal approximation to the Poisson law (consistent with ISO 11843-3 and ISO 11843-4) to compute decision thresholds, and it discusses the accuracy of that approximation (Annex B).

Key topics and requirements

• Scope and assumptions
  • Applicable when variations in background and signal are describable by the Poisson distribution.
  • Uses the normal approximation to derive variances, critical values and MDVs.
• Decision criteria
  • Defines the critical value (yC) for the response variable to control the probability of false detection (α, error of the first kind).
  • Defines the MDV (gx) tied to the probability of failing to detect a true signal (β, error of the second kind).
• Computation and reporting
  • Provides formulae for computing yC using standard-normal quantiles and observed means/variances (Clause 6).
  • Includes guidance on estimating mean and variance under normal approximation (Annex A) and examples (Annex D).
  • Specifies reporting requirements for capability assessments and applications (Clauses 7 and 8).
• Practical measurement constraints
  • Both signal and background must be raw, unprocessed counts.
  • Prefer longer single measurements over many short ones (improves normal approximation).
  • Repeat measurements are required to estimate means reliably.
  • Detector must operate in its linear counting range; number of channels and FWHM must match between blank and sample (Annex C).

Applications and users

• Targeted at laboratories and instrument operators using pulse-counting detectors and spectroscopy techniques where counts follow Poisson statistics:
  • X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS)
  • Electron and ion spectroscopy (AES, SIMS), and mass spectrometry (GC–MS)
• Typical uses:
  • Determining detection limits for hazardous-substance screening (e.g., RoHS testing).
  • Environmental monitoring, contamination control, material analysis.
  • Establishing decision thresholds in quality control and compliance testing.
• Users include metrology labs, analytical chemists, instrument manufacturers, and accreditation bodies.

Related standards

• ISO 11843 series (Parts 1–4) - general capability of detection principles and linear calibration cases.
• ISO 3534-1 - statistical vocabulary and symbols.
• ISO Guide 30 - reference materials terms.

Keywords: ISO 11843-6:2025, capability of detection, Poisson distribution, normal approximation, critical value, minimum detectable value, detection limit, pulse-counting, spectroscopy, XRF, XRD, GCMS.