The standard has been developed as a result of a European metrology project, ISOConCur led by National Physical Laboratory (NPL) in partnership with LGC.
Nanoparticles are increasingly used in innovative products manufactured by advanced industries and provide enhanced, unique properties of great commercial and societal value. The demand for high performance materials places increasingly stringent tolerances on nanoparticle properties including nanoparticle number concentration. This refers to the number of nanoparticles in a given volume of material and is an essential measurement to meet regulatory compliance across a range of industries. In nanomedicines, the measurement is required so as to obtain the correct dose of the active ingredient. It is also a useful metric to measure given intentional or accidental release of engineered nanoparticles into the environment at manufacturer plants or by end-users.
The measurement of the number concentration of nanoparticles is challenging for a number of reasons including instrumental limitations, lack of validated measurement protocols and reference materials for calibration, quality control and method validation. This standard is a step to address some of these issues.
The ISO standard provides an overview of nine techniques used to determine the nanoparticle number concentration in both liquid dispersions and aerosols. The methods described are the ensemble measurement techniques of differential centrifugal sedimentation (DCS), multi-angle dynamic light scattering (MDLS), small-angle X-ray scattering (SAXS) and ultraviolet-visible spectroscopy (UV-vis) and the particle counting methods of particle tracking analysis (PTA), resistive pulse sensing (RPS), single particle inductively coupled plasma mass spectrometry (sp-ICP-MS), condensation particle counter (CPC), and differential mobility analysing system (DMAS).
Each of these techniques has advantages and limitations that are detailed along with considerations on sample preparation and uncertainties. The standard also summarises the results of a recent international interlaboratory study where 50 laboratories determined the number concentration of 30 nm gold nanoparticles using five of the techniques discussed in the standard, to assess repeatability and reproducibility.
The standard will be published by ISO later this year and will provide a useful reference for industry, academia, regulators, and non-government organisations.
19 May 2022
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