Theoretical and Practical Aspects of a Comparison between Cascade Impactors (MOUDI, ELPI) and Electron Microscopy Results for Nanoparticles Analysis

Yves Cloutier (1), Alexandra Noël (2), Philippe Plamondon (2), Gilles L'Espérance (2), Chantal Dion (1), Ginette Truchon (1) , Joseph Zayed (1)

(1) Institut de Recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) 505, boul. De Maisonneuve Ouest, Montréal (Québec) Canada, H3A 3C2 (2) Département de chimie, Université de Montreal, CP 6128 Succursale Centre-Ville, Montréal (Québec) Canada, H3C 3J7

     Abstract Number: 180
     Last modified: April 28, 2010

Abstract
Impactors are commonly used in research on nanoparticles for exposure assessment. They allow to classify nanoparticles by their aerodynamic diameter and to predict their site of pulmonary deposition. In addition, electron microscopy grids are often used on impactor stages to enable evaluation of other parameters like size, shape and structure. The aim of this presentation is to discuss the use of impactors, such as MOUDI (Micro-Orifice Uniform Deposit Impactor) and ELPI (Electrical Low-Pressure Impactor), in experimental settings using TiO2 nanoparticles, in order to compare their results with electron microscopy images analysis methods. Data from images analysis has shown that the shape and the agglomeration state of TiO2 can vary between stages making the application of theory difficult for the prediction of others parameters. Electron microscopy, often used as a reference in toxicological studies, can give different measured diameters depending on the image analysis method and technique employed like Scanning Electron Microscopy (SEM) or Transmission Electronic Microscopy (TEM). Our results have also shown that depending on the combination of image acquisition techniques, we can observe measured diameters that are larger than the GMAD (geometric mean aerodynamic diameter) for some impactor stages and smaller for other ones. Measured diameters up to 5.8 and 4.1 GMAD have been observed for the MOUDI and the ELPI, respectively. On the other hand, measured diameters as low as 0.1 and 0.2 GMAD have been observed for the ELPI and MOUDI, respectively. Bias created by impactors, influence of the density and shape factors can partly explain these results. This study puts in light the fact that we should be very careful when measuring the sizes of particles in order to describe their toxicological properties since the measuring and analytical methods chosen for the analysis can greatly affect the conclusion.