Developing reference materials for mass spectroscopy to monitor radioactive and stable isotope pollution in the environment

The project

European Green Deal’s ambition for zero pollution requires the development of highly sensitive techniques to detect ultra-low amounts of pollutants and to determine their isotope ratios. Two such techniques are radiometry, which measures radioactivity, and mass spectroscopy, which measures the mass-charge ratio of particles and allows exact isotope compositions to be detected, even at low concentrations. Radiometry techniques have been well established for some time, but until the work of this project there was a lack of traceability and quality control for mass spectrometry.

Completed Metrology Partnership project Metrology for the harmonisation of measurements of environmental pollutants in Europe (21GRD09, MetroPOEM) helped to bridge the gap between radiometric techniques and mass spectrometry by comparing and linking both techniques. The reference materials and methods developed will support the characterisation and detection of polluting long-lived radionuclides, stable elements, and element tracers. This will significantly improve measurement uncertainties and detection limits.

The outputs from the project could be employed in fields including routine real-time monitoring, emergency response, geological dating and climate change studies through isotopic ratio measurements, and in other activities, such as nuclear forensics, decommissioning non-nuclear industries (such as the oil industry in the North Sea) and radiopharmaceutical facilities, where use is made of long-lived radioactive precursors. The collaboration between European laboratories established in this project is expected to continue beyond the end of the project.

Videos

The project consortium has produced a series of short training videos that are available on their website.

The titles of the videos are:

• Radionuclide Measurement by Mass Spectrometry
• The Basics of Gamma Spectrometry
• Production of liquid reference material for radionuclides
• Accelerator Mass Spectrometry for Actinide Research
• Production of solid reference material for radionuclides
• Stakeholder Workshop for Work Packages related to Stable Isotope Analysis
• Extraction Chromatography Resins
• The determination of Li and B isotope ratios by MC-ICP-MS with normalisation to an internal standard

Availability of new reference materials

• Radionuclide Standards: A series of single and mixed radionuclide standards were prepared, consisting of various actinides (²³⁴U, ²³⁶U, ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Am, mixed ^239/240Pu and U_nat) and ⁹⁰Sr. These were prepared from traceable standards at the NPL. All standards were characterised for activity level and stable and radioactive impurity content. These traceable radioactive standard solutions suitable for calibration of mass spectrometry instruments are now available for customers from NPL.
• Radioactive Reference Materials: Two radioactive reference materials were developed, one solid and one liquid, comprising ²³⁴U, ²³⁵U, ²³⁶U, ²³⁷Np, ²³⁸U, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am. Both reference materials were obtained by spiking a matrix with well-characterised starting solutions of individual radionuclides or a mixture of isotopes of the same element: U, Pu, Am and Np. Seawater was used as a matrix for the liquid RM, while the ‘multi-RN spiking mixture’ was added to two silica precursors for the solid RM. These silica precursors reacted by hydrolysis and condensation processes (sol-gel), and formed a solid tri-dimensional network with embedded radionuclides. The solid was ground to yield a synthetic sand-like material. The reference materials produced are available from CEA-LNHB (solid RM) and CMI (liquid RM) for distribution to the community.
• Certified Reference Material for stable isotope ratios: The certified reference material, UME MetroPOEM CRM, was produced in accordance with the requirements of ISO 17034:2016 standard. Seawater from the North Sea was used as the raw material. Considering the original and the target mass fractions of the elements the material was spiked by using NIST SRM 3100 series standards to obtain concentrations to be measured by analytical laboratories. The characterisation studies were conducted by an interlaboratory study where, in addition to the project partners, several expert organisations were also involved in isotope ratio measurements. All the assessments are based on the isotope ratio measurements conducted by using multi collector ICP-MS instruments except Ni for which mass fraction values determined by ICP-MS-MS were used for the assessment homogeneity and stability; thus only informative value is to be given in the certificate. The certified reference material is intended to be used for calibration of the instruments or quality control purposes in laboratories performing isotope ratio measurements.

Outcomes for relevant standards

The project had significant input to national and international written standards:

• DIN 51013:2023-07 Anorganische Isotopenanalytik - Begriffe und Verfahren 
• Assessment of absolute isotope ratios for the international isotope delta measurement standards
• Terminology and definitions of quantities relating to isotopic analyses
• Within ISO TC 147 SC3 WG14, a standard is being written on the determination of ²³⁷Np and Pu isotopes and this project has provided input into this standard. 

Longer-term economic, social and environmental impacts  

The outcomes of the project benefit the EU population via improved traceability of measurement through shorter and direct traceability chains, leading to improved analytical services that address pollution issues across the EU at lower cost and with more rapid sample turnaround. In turn, this better supports policy decisions and directives on the area of environmental pollution monitoring, with the longer-term effect of reducing health issues for individuals and improving the general environment of the EU member states.

Specific improvements include: 

• Implementation of new procedures and sample protocols developed within the project, 
• Better isotope ratio measurements of, and analytical techniques for Li, B, Ni, Cd and U by MC-ICP-MS 
• New calibration services for isotopes of Li, U and Pu by MC-ICP-MS 
• Establishment of production, characterisation and provision of traceable solid and liquid reference materials containing U, Np, Pu and Am for mass spectrometry measurements in general
• Establishment of production, characterisation and provision of liquid calibration standards containing U, Np, Pu and Am for mass spectrometry measurements in general 

Project coordinator Dirk Arnold from PTB said

‘Good news for metrologists: In MetroPOEM, we established the connection between the two SI units Bq (for activity) and mol (for amount of substance) for radioactive pollutants and we developed an SI-traceable primary measurement method for stable isotope ratios.’

This Metrology Partnership project has received funding from the European Partnership on Metrology, co-financed by the European Union Horizon Europe Research and Innovation Programme and from the Participating States.

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