Characterization of various metal nanoparticles by graphite furnace atomic absorption spectrometry: possibilities and limitations with regard to size and shape

Abstract

Graphite furnace atomic absorption spectrometry (GFAAS) is a promising technique for metal nanoparticle (NP) size characterization and differentiation from ions. However, so far only spherical gold (Au) and silver (Ag) NPs have been investigated. Therefore, in this work, non-spherical Au and Ag NPs, like rods and prisms, as well as other metal nanoparticles, like palladium (Pd), platinum (Pt) and zero-valent iron nanoparticles (nZVI) were examined. In the same way as previously shown for Au and Ag, nZVI can be distinguished from ionic Fe(III) due to a significant shift of absorbance signals to later times, i.e. by evaluation of the recently introduced parameter ‘atomization delay’ (t_ad). However, both iron species show the same behaviour regarding increasing iron concentration: t_ad is constant while the appearance time (t_AP) decreases. Furthermore, rod-shaped Au NPs and Ag nanoplates can be distinguished from the ionic form. A form discrimination, however, is not possible, since rods and plates are converted to spheres during the temperature program prior to atomization in the graphite furnace tube. The determined diameters of these in situ formed spheres are in good agreement with theoretical ones and diameters determined by scanning electron measurements (SEM). Hence, instead of one-dimensional parameters like width or length, volumes of the initial, non-spherical NPs can be determined by GFAAS. For Pd and Pt neither a differentiation between ions and NPs is possible nor a size discrimination of NPs.