A Proposal of Method for Evaluating Airborne MWCNT Concentration

As multi-wall carbon nanotubes (MWCNTs) come to be used in a wider range of products, increasing production is expected to result in greater exposure of workers to MWCNTs. In this research, we present a method for evaluating the concentration of MWCNT aerosols distinctively on the basis of the elemental carbon (EC) concentration. Respirable dust is sampled using a Sioutas cascade impactor (SCI) for a certain volume of workplace air. The SCI can collect size-segregated particles having aerodynamic diameters of 2.5 mu m, 1.0 mu m, 0.5 mu m, 0.25 mu m and <0.25 mu m. MWCNTs in sampled particles are determined by carbon analysis. Based on the phenomenon that MWCNTs easily aggregate/agglomerate, the present procedure for distinguishing MWCNTs uses the EC in particles larger than 1 mu m as an index of MWCNT; the EC is oxidized at a high temperature, 920 degrees C, in carbon analysis. We propose a three-step procedure for distinguishing between MWCNT aerosol and atmospheric particulate matter, and for measuring MWCNT concentrations in workplace air on the basis of EC concentration.