X-ray absorption fine structure (XAFS) experiments in fluorescence mode have been performed in total reflection excitation geometry and conventional 45°/45° excitation/detection geometry for comparison. The experimental results have shown that XAFS measurements are feasible under normal total reflection X-ray fluorescence (TXRF) conditions, i.e. on droplet samples, with excitation in grazing incidence and using a TXRF experimental chamber. The application of the total reflection excitation geometry for XAFS measurements increases the sensitivity compared to the conventional geometry leading to lower accessible concentration ranges. However, XAFS under total reflection excitation condition fails for highly concentrated samples because of the self-absorption effect.
The distribution and speciation of zinc were studied in the body of female specimens of the soil-inhabiting, plant-feeding nematode, Xiphinema vuittenezi treated with nano-ZnO and its bulk counterpart. Lyophilized nematodes were studied by X-ray absorption near edge structure spectrometry (XANES) in order to characterize the zinc speciation. Furthermore, in the cross-sections prepared by focused ion beam technique, elemental maps were obtained using the electron probe microanalysis (EPMA) technique. XANES spectra were collected from three different regions (head, midbody and tail region) of nematodes in case of two different treatments (50 mg/L bulk and nano-ZnO suspension, 24 h long treatment). The sample spectra were fitted by the spectra of several reference compounds, the main components of the fitted spectra are the following in all cases: bulk/nano-ZnO; ZnHis and Zn3(PO4)2 * xH2O. Consequently, partial biotransformation takes place for both treatments, histidine- and phosphate-rich ligands play dominant role in the binding of zinc. According to the result of the EPMA analysis, it can be established that the distribution of zinc correlates with the calcium and phosphorus distribution for both treatments. Considering the results of the investigations performed by the two microanalytical techniques, it is likely that calcium phosphate granules were formed in order to bind zinc and hereby to take part in zinc detoxification. Apparent difference in the behavior of bulk and nano-sized ZnO in the body of the investigated nematodes was not found.