High-resolution continuum source graphite furnace atomic absorption spectrometry for the monitoring of Au nanoparticles
This work investigates the possibility of obtaining information on the chemical form (ionic or as Au nanoparticles (NPs)) in which Au is found in solutions by means of high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS), without the need to use any additional separation step or any extra technique. It is demonstrated that proper optimization of the temperature program, using a very slow heating ramp (150 °C s−1) during the atomization step and a sufficiently high atomization temperature (2200 °C) in the absence of chemical modifiers, enables a fast and simple screening to be performed, since the signal profiles obtained for solutions/suspensions of ionic Au and AuNPs are very dissimilar. Moreover, in the case of finding NPs, it is possible to estimate the average particle size, because this parameter appears to be directly related with the time of appearance of the maximum peak height (a value of 27.7 nm ± 8.8 nm was estimated for NIST Reference Material 8012 Gold nanoparticles, nominal 30 nm diameter). The proposed procedure offers a limit of detection of 5.5 pg (0.55 μg L−1) and a linear range up to 10 ng (1000 μg L−1), and was further validated by spiking a natural water certified reference material (CRM KEJIM 02). The occurrence of mixtures of ionic Au and AuNPs seems to be more complicated to resolve if quantitative information is aimed at (e.g., calculating the exact amount found in each form) because, even though the mixture behaves as predicted by summing the individual signals of ionic Au and AuNPs, signal overlaps can be anticipated and, thus, proper signal deconvolution should be carried out.