ISO 20289:2018

Overview

ISO 20289:2018 - "Surface chemical analysis - Total reflection X‑ray fluorescence analysis of water" is an international standard that specifies a validated laboratory method for elemental analysis of water using Total Reflection X‑Ray Fluorescence (TXRF). It is written for technicians and routine testing laboratories (including those accredited to ISO/IEC 17025) that perform large numbers of water analyses. The document defines good practice for TXRF measurements of dissolved elements in drinking water, surface water and groundwater, and addresses interferences, instrument calibration, quantification and uncertainty.

Key topics and requirements

• Scope and limits: Method applies to dissolved elements; sampling, dilution and pre‑concentration are excluded. Elements determinable depend on the TXRF instrument’s X‑ray source.
• Working range and limits of quantification (LOQ): In relatively unpolluted waters LOQs are typically between 0.001 mg/L and 0.01 mg/L for most elements; typical working range is about 0.001 mg/L to 10 mg/L, depending on element and matrix.
• Interferences and matrix effects: Electrical conductivity should be below 2 mS/cm; suspended solids, high salt matrices (e.g., seawater) and overlapping peaks can affect accuracy and may require dilution or filtration.
• Apparatus and labware: Clean, calibrated glassware or suitable plastics; lab cleanliness, reagent purity and air‑handling strongly influence blank contamination and quantification limits.
• Procedure elements: Sample preparation environment, specimen deposition on carriers, use of an internal standard (e.g., Annex B example using Mo X‑ray source with Ga internal standard), instrument calibration, detection limit determination, spectra fitting and quantification calculations.
• Quality assurance: Instrument performance samples, external quality control materials, measurement uncertainty (GUM approach), precision/repeatability requirements and routine reporting formats.
• Safety: Addresses X‑ray radiation hazards - appropriate shielding and handling procedures are required.

Applications and users

• Routine elemental screening and quantification of dissolved metals and trace elements in drinking water, groundwater and surface water.
• Applicable to environmental testing laboratories, water utilities, contract analytical labs and research groups using TXRF for high‑throughput water analysis.
• Useful for quality control programs where rapid, low‑volume sample analysis is needed and where labs follow ISO/IEC 17025 quality systems.

Related standards

Key normative references cited by ISO 20289:2018 include:

• ISO 3696 (water for analytical laboratory use)
• ISO 5667‑1 / ISO 5667‑3 (sampling guidance)
• ISO 5725‑1 / ISO 5725‑2 (accuracy and precision)
• ISO 14706, ISO 17331 (TXRF methods on surfaces)
• ISO/TS 18507 and the JCGM GUM series (uncertainty evaluation)

Keywords: ISO 20289:2018, TXRF, total reflection X‑ray fluorescence, water analysis, limit of quantification, internal standard, laboratory quality control.