ISO 11843-6:2019

Overview

ISO 11843-6:2019 - Capability of detection, Part 6 - provides a statistical methodology for determining the critical value and the minimum detectable value (MDV) when measurement counts follow a Poisson distribution and are approximated by the normal distribution. The standard is consistent with other parts of the ISO 11843 series and is targeted at pulse‑counting instruments (for example, XRD, XRF, XPS, AES, SIMS, GC‑MS) where both signal and background variations can be modelled as Poisson processes. Annex C discusses the accuracy of the normal approximation versus the exact Poisson distribution.

Key topics and requirements

• Scope and applicability: Applicable when both background noise and signal counts are Poisson distributed and the conventional normal approximation is acceptable.
• Decision criteria: Defines the critical value for the response variable used to decide whether a signal is present, using predefined error probabilities α (type I error) and β (type II error).
• Estimation and variance: Uses sample means to estimate means and variances under the normal approximation (see Annex B for estimation guidance).
• Sufficient capability criterion: Provides rules to assess whether a detection system meets required confidence (1 − β) for a specified MDV.
• Measurement protocol constraints:
  • Raw counts must not be pre‑processed (no smoothing).
  • Measurement duration and detector channel width should be fixed and reported.
  • Prefer longer single measurements over many short ones to improve normal approximation.
  • Number of detector channels and peak width (FWHM) must be consistent between blank and sample (Annex D).
• Reporting requirements: Specifies what to include when reporting capability assessments and application results (Clause 6–7).
• Supporting material: Annexes include symbols (A), estimation methods (B), approximation accuracy (C), channel selection (D), and worked examples (E).

Applications

ISO 11843-6:2019 is practical for:

• Laboratory analysts and metrologists performing detection limit assessments for pulse‑counting detectors.
• Instrument manufacturers establishing detection performance of spectrometers and counters.
• Environmental and safety testing (e.g., asbestos, crystalline silica) and regulatory compliance testing (e.g., RoHS verification by XRF or GC‑MS).
• Quality assurance in semiconductor contamination and surface analysis where low‑level detection decisions are required.

Who should use this standard

• Analytical laboratories, instrument developers, accreditation bodies, and quality managers who need statistically sound procedures to define minimum detectable values and to document measurement capability.

Related standards

• ISO 11843‑1, ISO 11843‑2, ISO 11843‑3, ISO 11843‑4 (Capability of detection series)
• ISO 3534‑1 (Statistics - vocabulary)
• ISO Guide 30 (Reference materials - terms and definitions)

Keywords: ISO 11843-6:2019, capability of detection, Poisson distribution, normal approximation, critical value, minimum detectable value, detection limit, pulse counting, XRF, XRD, GC‑MS.