Enhancing particle size characterization performance through proficiency testing program: result and insights from inter-laboratory comparison

Abstract

The proficiency testing (PT) for particle size characterization by inter-laboratory comparison was organized by the dimensional metrology department of the National Institute of Metrology Thailand (NIMT). This program aims to enhance and to expand the efficiency and capability of testing laboratories in the field of particle size characterization using various techniques, including atomic force microscope (AFM), transmission electron microscope (TEM), scanning electron microscope (SEM), and dynamic light scattering (DLS). The measurement range covers nanometer to micrometer scale. These instruments are importance for research and development especially to nanotechnology related industries. The PT program was conducted in 2022 where five artifacts were used: monodispersed gold nanoparticle (diameter 20 nm), monodispersed polystyrene particle (diameter 100 nm, 500 nm, and 1500 nm) and monodispersed silica oxide particle (diameter 100 nm). The monodispersed polystyrene particles, diameter 100 nm and 1500 nm are certified reference materials (CRMs). These two artefacts were used as the reference to evaluate accuracy of participant laboratories. The other 3 artefacts are reference material under development. Hence, the assigned values were calculated from consensus among all participants. To evaluate the performance of participant laboratories, En values and z-scores were calculated for each artefact and each measuring technique. The assessment of participant performance through performance scores allows the participant to determine how accurate and how appropriate the measurement results and measurement uncertainties evaluation are. From the results, unsatisfied results can be categorized into three scenarios. First, the measurement uncertainties were not appropriately evaluated. Secondly, measurands obtained from all measuring techniques are not the same. Lastly, the magnification used in microscopy techniques plays a crucial role to resolution and accuracy of size determination.