Overview
ISO 21253-1:2019 - "Water quality - Multi-compound class methods - Part 1" defines objective criteria for the mass spectrometric identification of target compounds in water and other environmental samples. It is a guidance/criteria document to be used together with analytical methods for specific compounds and covers both gas chromatography–mass spectrometry (GC‑MS) and liquid chromatography–mass spectrometry (LC‑MS) workflows for multi‑compound class analyses.
Key topics and technical requirements
- Three-step identification workflow
- Step 1 - Chromatographic separation: confirm relative retention time against a retention time standard before proceeding.
- Step 2 - Mass spectrometric evaluation: collect identification points from MS data (full scan, SIM, SRM/MRM, HRMS etc.).
- Step 3 - Additional analytical confirmation where required.
- Identification decision rules
- Classified as identified when ≥ 3 identification points are obtained.
- Indicated when 1–2 identification points are obtained.
- Absent (below detection limit) when no identification points are obtained.
- Retention time tolerance
- Relative retention time must match the calibration standard within ±0.5% for GC and ±2.5% for LC.
- Mass spectrometry performance
- Minimum scan rate: 7 scans per chromatographic peak.
- Low‑resolution MS: peak width at half‑height ≤ 0.7 Da on tune masses; full scan mass range lower limit ≈ m/z 35 to (target mass + 10 u).
- High‑resolution MS (HRMS): resolution > 10 000 FWHM, mass accuracy typically ≤ 5 ppm.
- Full‑scan identification requirement
- Diagnostic ions (molecular ion, characteristic fragments/adducts/isotopes) with relative intensity > 10% in the reference spectrum must be present.
- Definitions and supporting elements
- Uses terms such as diagnostic ion, identification point, retention time standard, and relative retention time (see ISO 6107 vocabulary).
Practical applications and users
ISO 21253-1:2019 is intended for laboratories and organizations performing environmental monitoring, regulatory compliance testing, and multi‑residue screening of water, wastewater and other environmental matrices. Typical users:
- Environmental and public health laboratories
- Water utilities and wastewater treatment labs
- Contract testing laboratories offering multi‑compound GC‑MS and LC‑MS analyses
- Method developers and QA/QC specialists implementing standard‑based identification criteria
The standard helps ensure reproducible, defensible identification decisions in multi‑compound class methods and supports reporting categories (identified, indicated, absent) used in regulatory and research contexts.
Related standards
- ISO 6107 - Water quality vocabulary
- ISO 22892 - referenced as a general basis for MS identification principles
- EN 16693 - identification points principle (referenced)
- See Annexes A–D of ISO 21253‑1 for technique recommendations, full‑scan criteria, diagnostic ions and examples of identification‑point calculations.
Open preview (PDF)Water quality — Multi-compound class methods — Part 1: Criteria for the identification of target compounds by gas and liquid chromatography and mass spectrometry
