A new certified reference material for size and shape analysis of nanorods using electron microscopy

Vikram Kestens,Gert Roebben,Andrea Held,Tsvetelina Gerganova

doi:10.1007/s00216-020-02984-z

Abstract

A new certified reference material (CRM) for size and shape analysis of elongated nanoparticles has been developed by the European Commission’s Joint Research Centre. The CRM consists of titanium dioxide nanorods dispersed in 1-butanol, was coded ERM-FD103 and has been certified for different electron microscopy–based operationally defined measurands such as the modal and median values of the particle number-weighted distributions of the minimum and maximum Feret diameter, the maximum inscribed circle diameter, the area-equivalent circular diameter and the aspect ratio. The nanorods have nominal dimensions of 15 nm in width and 55 nm in length. Homogeneity and stability measurements were performed using transmission electron microscopy. The relative standard uncertainty for homogeneity ranged from 0.3 to 1.7%. No significant instability was detected for a shelf life of 18 months and a storage temperature of 18 °C. The certified values have been determined from the results of an interlaboratory comparison in which qualified expert laboratories participated with scanning and transmission electron microscopy. The certified values are traceable to the unit of length in the International System of Units, the metre, and the relative expanded uncertainties (confidence level of approximately 95%) range from 4 to 6%. These properties allow the CRM to be used for quality assurance and calibration of electron microscopy methods for nanoparticle size and shape analysis in ranges relevant for the implementation of EU legislation related to nanomaterials. The presented study discusses the purpose and results of the different steps that were followed to turn an industrially relevant raw titanium dioxide nanorod material into a fit-for-purpose CRM.Graphical abstract

Highlights

Nanoparticles, as well as materials containing them, are widely used in many applications and products because of their desirable unique chemical and physical properties
Joint Research Centre (JRC) has developed and produced a number of certified reference material (CRM) that consist of monomodal and bimodal populations of silica nanoparticles with a near-spherical shape and nominal diameters in the range of 20 to 90 nm
These CRMs have been advantageous for analytical purposes such as validation and quality control of measurement procedures for size analysis of nanoparticles

Summary

Introduction

Nanoparticles, as well as materials containing them, are widely used in many applications and products because of their desirable unique chemical and physical properties. Significant advances have been made in the development and optimisation of new and existing techniques for size analysis of (nano)particles [8]. Most of these techniques do not directly measure true particle size but, instead, infer size from results obtained for other particle-related physical properties such as sedimentation times or diffusion rates [9]. Unless the particles have a perfectly spherical shape, equivalent diameters obtained from various techniques can differ significantly due to different physical measurement principles and data analysis strategies [10]. When dealing with the implementation of the Commission’s nanomaterial definition, the use of analytical procedures that determine equivalent diameters rather than true minimum external dimensions can lead to biased results and inconclusive assessments

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