Matrix CRM of sewage sludge METRANAL® CRM AN-OK01

Importance of the Topic

This summary addresses the development and certification of a reference material (CRM) based on sewage sludge enriched with selected persistent organic pollutants and trace elements. Certified reference materials are essential for ensuring metrological traceability, validating analytical methods, and harmonizing measurements across laboratories in environmental monitoring, waste management, and regulatory compliance.

Study Objectives and Overview

The primary aim was to prepare a homogeneous sewage sludge CRM (AN-OK01) containing certified values for seven PCB congeners, twelve PAH compounds, and multiple element concentrations. The material was produced by spiking a natural sludge matrix with target analytes, followed by milling, irradiation, and rigorous characterization.

Methodology and Sample Preparation

The production process involved:

• Sieving and milling the sludge to a particle size below 100 µm.
• Spiking with calibrant solutions of PCBs and PAHs.
• Stabilization by gamma irradiation (25 kGy) to prevent biotransformation.
• Extraction of elements by aqua regia (ISO 11466) and organic compounds by EPA protocols (EPA 8081, 8082A, 8310).

Short-term stability and homogeneity were assessed in accordance with ISO Guide 35.

Instrumentation

• Gas chromatography (GC) and high-performance liquid chromatography (HPLC) for PCBs and PAHs.
• Flame and electrothermal atomic absorption spectrometry (FAAS, ETA-AAS).
• Inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) for elemental analysis.

Main Results and Discussion

Certified and indicative values (all dry-mass corrected at 105 °C) include:

• PCB congeners: concentrations ranging from 41 to 307 µg·kg⁻¹ with expanded uncertainties (k=2).
• PAH compounds: concentrations from 0.20 to 5.46 mg·kg⁻¹ with k=2 uncertainties; several lower-level analytes are indicative only.
• Elemental extractable fractions: As, Cd, Cr, Cu, Hg, Ni, Pb, Zn and others, spanning low µg·kg⁻¹ up to tens of g·kg⁻¹ (e.g., Ca ~23 550 mg·kg⁻¹), and major nutrients (N, P).

Agreement among at least two independent methods and multiple laboratories underpinned certification. Characterization uncertainty dominated the combined expanded uncertainty budgets.

Benefits and Practical Applications

• Ensures comparability and accuracy in environmental monitoring of sludge contamination.
• Supports method validation, instrument calibration, and quality control in laboratories.
• Enables interlaboratory studies and proficiency testing for waste analysis.

Future Trends and Potential Applications

Emerging priorities include extending CRM portfolios to cover novel contaminants (e.g., microplastics, pharmaceuticals), enhancing commutability with diverse sludge types, and integrating stable isotope-labelled spikes for compound-specific isotope dilution assays. Advanced certification methods combining high-resolution mass spectrometry and nuclear magnetic resonance (NMR) may further reduce uncertainties.

Conclusion

The AN-OK01 sewage sludge CRM offers a well-characterized, stable, and homogeneous tool for laboratories to achieve traceable and reliable measurements of PCBs, PAHs, and trace elements. Its certification under ISO Guide 31 and ISO 17034:2017 standards assures suitability for method validation and quality assurance in environmental and industrial analytics.

References

• ISO Guide 31, Reference Materials—Contents of Certificates.
• ČSN EN ISO 17034:2017, General Requirements for the Competence of Reference Material Producers.
• ČSN EN ISO/IEC 17025:2018, General Requirements for the Competence of Testing and Calibration Laboratories.
• ČSN EN ISO 9001:2016, Quality Management Systems Requirements.