Separation and determination of arsenic and selenium in natural water samples by energy dispersive X-ray fluorescence

This work had as main objective to study a method for separation and determination of Arsenic (III) and (V), and Selenium (IV) and (VI) present in aqueous solutions at trace level. For this purpose a preconcentration method based on the adsorption of the elements in activated charcoal loaded with zirconium (ZrC*) was used. The ion As (III) was better absorbed onto 200 mg ZrC* in pH 8, while, the ion As (V) presented better results when the absorption was carried out onto 100 mg ZrC* with the pH adjusted for 2. The ions Se (IV) and Se (VI) presented a better absorption when the solutions were adjusted for pH 4, but with different masses of ZrC*, 200 mg for Se (IV) and for Se (VI) just 100 mg. The detection limits obtained by the X-ray fluorescence were 0.050 mg.L-1 and 0.009 mg.L-1 for As (III) and As (V), respectively. In the case of selenium the limits were 0.011 mg.L-1 and 0.016 mg.L-1 for Se (IV) and (VI) species, respectively. The errors obtained by this methodology were smaller than 2% for the ion As (III) and smaller than 1% for As (V), Se (IV) and Se (VI). (author)