The first ISO Technical Standard for nanoparticle concentration
Challenge
Nanoparticles (NPs) are extremely small – less than 100 nm in size. Due to their high surface area, nanoparticles often have increased activity. This has led to their use in a wide range of modern products, including sunscreen, fuel cells, semiconductors, drug and gene delivery vehicles, or as contrast agents for Magnetic Resonance Imaging.
However, a common issue is batch-to-batch variability, with over half of NPs produced for high performance applications failing to meet specifications. Numerous cycles of production and measurement are required to develop reproducible processes.
The nanotechnology sector is also an area where product innovation is developing faster than the techniques required to ensure compliance with regulatory frameworks. This is especially the case for determining the concentration of nanoparticles in suspension – the knowledge of which is required to optimise and reproduce formulations and products. In most cases, this number concentration is not known but is calculated upon the basis of assumptions and mass-balance considerations.
The direct determination of number concentration for nanoscale particles is challenging. Documentary standards need to be developed within the International Organization for Standardisation (ISO) to measure this parameter. A lack of validated measurement protocols, reference materials for calibration or quality control has hindered the establishment of metrological traceability.
Solution
The Innanopart project developed and validated a wide range of techniques for accurately measuring nanoparticle number concentrations. In addition, as a world first, gold colloidal nanoparticle reference materials were characterised and validated.
Based upon these results, a VAMAS intercomparison (TWA34, Project 10) was launched using the reference material and the techniques developed. A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles. The study identified best practice to improve accuracy by a factor of five. As the need for standardisation in nanoparticle characterisation was marked as an area of high priority, the chair of ISO/TC 229 ‘Nanotechnologies’ asked that the underlying metrology developed in the project be adapted and published as an ISO Technical Report in order to meet ongoing industry and legislative needs.
Impact
Based upon the work performed in the Innanopart project, in 2019 a new EURAMET project was launched, ISOCONCur, in order to adapt these results into a working ISO Technical Specification.
This was successful, and in November 2023 the new ISO standard was published: “ISO/TS 24672:2023 Nanotechnologies — Guidance on the measurement of nanoparticle number concentration”. This document provides an overview of the methods used to determine nanoparticle number concentration in liquid dispersions and aerosols.
Much of the data it contains was derived from the methods developed in Innanopart including DCS, SAXS, UV-vis, PTA, CPC and spICP-MS, providing information on the use of each technique, along with considerations on sample preparation, advantages and limitations.
The standardised and validated measurements it details will enable the industrial and pharmaceutical industries utilising these particles to demonstrate compliance with EU regulations linked to the definition of nanomaterials (2011/696/EU). It will also help allow the European Chemical Agency (ECHA) to more accurately evaluate the properties of new nanomaterials submitted for authorisation under ‘Registration, Evaluation, Authorisation and Restriction of Chemicals’ (REACH) legislation (Regulation (EC) 1907/2006).
In addition, the new Technical Report will help contribute to an improved acceptance of nanotechnology and nanotechnology-based products by society and provide a basis for more reliable, efficient and new products with higher performance.
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