R. Fernández-Ruiz

First approximation to the analysis of Ru and Se in carbon nanoparticles as a new voltaic pile system by TXRF

This work presents the first analytical study carried out by total-reflection X-ray fluorescence (TXRF) in the special system constituted by carbon nanoparticles impregnated with Ru and Se, which is currently being investigated as an alternative voltaic system. This study shows that conventional analytical techniques, such as atomic absorption spectroscopy (AAS) or inductively coupled plasma spectroscopy (ICPS), can produce large deviations in the metallic contents of this material, as high as 50%, due to recovery problems, mainly of Ru, in the acid leaching process. This fact can have important consequences in related research, industrial fabrication and for their environmental impact. An alternative methodology based on the quantitative direct solid analysis of metallic impregnated carbon nanoparticles by means of the TXRF technique has been developed. The suspension conditions have been optimized by the use of different programs of ultrasonic pulses, and it has been characterized by dynamic light scattering (DLS) with the aim of checking the final size distribution of the particles. This methodology has been checked for different sample size distributions of the suspension. A microscopical image and scanning electron microscopy (SEM) of the solid depositions over the TXRF sample carrier have also been performed to evaluate homogeneity from a macroscopic and microscopic point of view and, additionally, to evaluate the possible presence of matrix effects. Finally, the TXRF results were validated by means of inductively coupled plasma mass spectrometry (ICP-MS), in a direct solid way, and by elemental analysis (CHNS), which confirmed the validity of the TXRF quantitative direct solid measurements. From an analytical point of view, the more important result was the strong correlation found between the particle size distributions and the homogeneity of the depositions with respect to the uncertainty of the Ru and Se TXRF measurements, but not with respect to their nominal values. The optimum uncertainties obtained with the developed methodology were 5.9% and 2.9% for Ru and Se, respectively, for a coberture factor k = 2 (95%). Finally, the application of ICP-MS to the analysis of solid samples by suspension method has proven to be a non trivial task, at least for this nanoparticle system. The results obtained in this work indicate that the adequate modification of the fundamental ICP-MS parameters, i.e. dilution factor, RF power and nebulizer gas flow, could be the initial way to optimize the analytical results by ICP-MS.

Study of bioaccumulation kinetics of chromium(VI) in Acinetobacter beijerinckii type bacterium by Total Reflection X-Ray Fluorescence Spectrometry

Total Reflection X-Ray Fluorescence (TXRF) has been applied for the first time to evaluate the kinetic behavior of the Cr(VI) bioaccumulation process that the recently isolated bacterium, named ANCR (Acinetobacter beijerinckii type), presents. First, a qualitative study of the bacterium elemental profile detected by TXRF has been carried out. Second, detection limits and the uncertainty of the technique were evaluated for this case. Finally, an experiment was designed to evaluate the behavior of the chromium content by two ways: in the cultured medium of the experiment, evaluating its decrease, and bioaccumulated in the bacteria, evaluating its increase. The results demonstrate that this new strain of Acinetobacter bacterium is able to reduce the chromium present in the culture medium. As a consequence, it can be used as a promising microorganism for Cr(VI) bioremediation from polluted wastewaters. Finally, TXRF has shown its versatility, potential and sensitivity for the analytical evaluation of toxic metals in this kind of microbiological system.

Eu and Tb quantitation in luminescent γ-ZrP-organometallics compounds by TXRF direct solid procedure

This work presents the analytical procedure developed to quantify Eu and Tb lanthanides by Total-reflection X-Ray Fluorescence (TXRF) by a direct solid method for first time. These rare-earth elements are doping the organic-inorganic hybrid compound γ-ZrP-TerPy which is currently being investigated as a highly efficient luminescent system. The developed procedure allows for the analysis of very low sample quantities, ca. 5 mg, with an adequate expanded uncertainty, around 8%, and detection limits lower than 0.002 wt% for Eu and Tb. The hereby described direct solid procedure has been tested against the usual quantitative analysis by means of the acid digestion of the samples by TXRF and ICP-MS. Discrepancies as large as one order of magnitude were found between the direct and the acid-digestion measurements. The combination of several unanticipated chemical effects, produced in the conventional digestion procedure of this material, explain its strong loss of Eu and Tb. The thorough optimization of the digestion procedures finally confirmed the validity of the easy and simple direct procedure carried out by TXRF in a solid way without sluggish sample digestion. This research shows once again the versatility and confidence of the quantitative direct solid measurements performed by TXRF.