September 2014 Archives

So far, high-resolution microscopic analysis of individual atmospheric particles has been fairly difficult because of problems with the filters used for capturing particles. The research group in the National Institute for Standards and Technologies, United States, is proposing a multiplatform approach for microscopically assessing chemical and optical properties of individual heterogeneous urban dust particles. The procedures described in the paper could also be useful for similar analysis. The method uses 5 steps; (i) particles embedded in fibrous filters are transferred to polished silicon/germanium wafers with electrostatically-assisted high-speed centrifugation, (ii) particles with light absorbing/scattering behavior are identified from bright/dark field light-microscopy, (iii) particles identified from light microscopy are compositionally mapped at high-definition with field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy, (iv) compositionally-mapped particles are further analyzed with focused ion-beam (FIB) tomography whereby a series of thin slices from a particle are imaged, and the resulting image stack is used to construct a 3-dimensional model of the particle, and (v) particle chemistry is assessed over two distinct regions of a thin FIB slice of a particle with energy-filtered transmission electron microscopy (TEM) and electron energy-loss spectroscopy associated with scanning TEM. For more information, see the paper, "Qualitative Multiplatform Microanalysis of Individual Heterogeneous Atmospheric Particles From High-Volume Air Samples", J. M. Conny et al., Anal. Chem., Just Accepted (DOI: 10.1021/ac5022612 Publication Date (Web): September 14).