ISO 54321:2020

Overview

ISO 54321:2020 defines standardized procedures for the aqua regia digestion of solid environmental matrices - soil, treated biowaste, sludge and waste - to extract the aqua regia soluble fractions of elements for subsequent instrumental analysis. The standard specifies two digestion approaches (thermal atmospheric and microwave closed-vessel) and clarifies that aqua regia does not necessarily produce total decomposition; results represent the aqua regia–soluble metal fraction that is considered fit for many environmental protection and monitoring purposes.

Key topics and technical requirements

• Scope and applicable elements: Validated for a wide range of metals/metalloids including Al, As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, Zn and others. Users may apply the procedure to additional elements after verification.
• Two main methods:
  • Method A - Thermal (atmospheric)
    • A1: Reflux for (120 ± 10) min.
    • A2: Heating block at (105 ± 5) °C for (120 ± 10) min.
  • Method B - Microwave (closed vessels)
    • Temperature-controlled digestion at (175 ± 5) °C for (10 ± 1) min.
• Principles of analysis: Digest a defined test portion with aqua regia (1 volume HNO3 : 3 volumes HCl by mass fractions given in the standard) followed by filtration/centrifugation and instrumental determination.
• Quality control and contamination control:
  • Use analytical-grade reagents and procedural blanks.
  • Clean and select sample containers to avoid contamination (e.g., glass can release Al, B, Na, K; polyethylene may allow Hg loss).
  • Validate filtration and sample-contact materials for the target analytes.
• Safety and laboratory practice:
  • Highly corrosive, oxidizing acids and high temperature/pressure operations require fume hood, trained personnel and certified microwave digestion equipment (domestic microwaves prohibited).
  • Do not open pressurized vessels until cooled.

Practical applications and users

ISO 54321:2020 is intended for:

• Environmental testing laboratories performing trace metal analysis in soils, sludges, composts, biowaste and industrial wastes.
• Regulatory agencies and consultants conducting compliance monitoring, risk assessment and remediation evaluations.
• Waste management and treatment facilities needing consistent data on metal solubility/availability.
• Research groups studying metal partitioning, mobility, and environmental impact.

This method supports routine multi-element analysis prior to ICP-MS, ICP-OES or AAS measurement and helps ensure comparability of data used for environmental protection decisions.

Related standards

• ISO 11466 (aqua regia reflux procedures)
• EN 13657, EN 16174 (European procedures for similar matrices)
• NEN 6961 (heating block procedure source) These documents contain similar approaches and are referenced for comparability and method choice.

Keywords: ISO 54321:2020, aqua regia digestion, soil digestion, sludge analysis, biowaste, microwave digestion, reflux digestion, trace metals, environmental analysis, sample preparation, laboratory safety.