Aerosol nanostructure study with porous grids - A review
Résumé
The study of particle morphology is a key step in risk assessment related to the inhalation of nanoparticles. The analysis is generally ensured by TEM (Transmission Electronic Microscope). Up-tonow, using porous TEM grid is one of the easiest technique to provide samples. On the one hand, the present communication reviews applications using the technique, and on the other hand, provides feedback from the state of the art to support the set of sampling time, which is a key parameter for users. The sampling on porous grid technique has been introduced by VTT (Lyyränen 2009) and assessed by INERIS developing and using a Mini Particle Sampler (MPS, www.ecomesure.com), both in a theoretical and experimental point of view (R’mili 2013). AIST (Ogura 2014) confirmed these results. The main interest of this technique is that the sampling support is also the support of analysis. The MPS sampler is low cost, portable and easy to use. The grid is immediately available for analysis as soon as the sampling is stopped. A state of the art about the use of MPS shows there is a growing number of applications. Regarding nanosafety, the MPS is carried out for exposure assessment at the workplace as well as the study of emissions from powder handling, dustiness testing, mechanical solicitation of end-products, processes (e.g. deposit of nanoparticles on textiles), exposure of consumer, end of life (e.g. characterization of incineration fumes), characterization of exposure during in vivo and in vitro toxicological studies, etc. Some Guidance or future Standards are supporting the use of MPS. Applications appear also in other fields, such as car exhausts, road particle release, exposure in cars, air quality in clean rooms, worker exposure to diesel fumes or brakes emissions, etc. The sampling time is an important parameter to consider for providing good samples to the microscopist. It is recommended to each user of MPS to feed-back his own experience from his specific sampling conditions. Such an approach is illustrated on the Figure below where optimized sampling time has been plotted versus the related total number concentration provided by a CPC in the submicronic range. This feed-back is based mostly on studies conducted at a flow rate of 0.3 lpm in various contexts. As a result, the operator can assess the order of magnitude of the sampling time by using the total number concentration measured simultaneously in real time.