ISO 15238:2025

Overview

ISO 15238:2025 specifies a laboratory procedure for the determination of the total cadmium mass fraction in coal. The method combines controlled ashing of a representative coal sample with dissolution of the ash and quantification by graphite-furnace atomic absorption spectroscopy (GFAAS/AAS). This third edition updates normative references and refines calculation formulae; it is intended for routine monitoring, quality control and regulatory assessment of cadmium in coal.

Key Topics

• Principle: Coal is ashed, the ash is dissolved (aqua regia + hydrofluoric acid), complexed with boric acid and analysed by graphite-furnace AAS for cadmium quantification.
• Sample preparation: Prepare representative test samples in accordance with ISO 13909-4 or ISO 18283 and equilibrate moisture before analysis.
• Ashing conditions: Place samples in silica or platinum crucibles and raise to (450 ± 10) °C, maintaining that temperature for at least 2 h (minimum overall ashing time 3 h; up to 18 h allowed).
• Reagents and standards: Use analytical-grade reagents (Grade 1 water per ISO 3696). Key reagents include aqua regia, concentrated hydrofluoric acid, saturated boric acid and certified cadmium standard solutions (stock and working solutions).
• Instrumental analysis: Calibration uses matrix-matched standards (examples: 0.0, 1.0, 2.5 and 5.0 µg/l) and instrument verification with certified reference materials. No additional matrix modifier is required when appropriate furnace parameters are used.
• Quality assurance: Prepare blank solutions, perform duplicate determinations and record the mean result to the nearest 5 ng/g on the "as analysed" basis.

Applications

• Routine environmental and occupational monitoring of cadmium in coal feedstocks and products.
• Laboratory quality control for coal analysis and certification programs.
• Supporting regulatory compliance and risk assessments where cadmium reporting is required.

Practical notes from the standard:

• Exercise caution handling corrosive and toxic reagents (HF is highly hazardous).
• Microwave or pressurized-vessel dissolution of ash may be used as an alternative if quantitative cadmium recovery is demonstrated.
• The method has not been validated for coals that spontaneously ignite; users must validate performance before applying the procedure to such samples.

Related Standards

• ISO 3696 - Water for analytical laboratory use
• ISO 13909-4 - Coal sampling and test-sample preparation
• ISO 18283 - Manual sampling of coal and coke
• ISO 5068-2 and ISO 11722 - Moisture determination methods

This standard is prepared by ISO/TC 27/SC 5 (Coal and coke methods of analysis) and replaces ISO 15238:2016. For implementation, consult the full ISO 15238:2025 document and national standards body guidance.