A Green Analytical Method for Pre-concentration of Uranium in Water Samples Using Minicolumn with Sugarcane Bagasse

Abstract

This study proposes a method based on solid-phase extraction using a minicolumn with sugarcane bagasse for pre-concentration uranium in water samples. The first optimization step was used factorial design in two levels (25) for the preliminary assessment of factors: elution flow, sample flow, pH, buffer concentration, and eluent concentration. From this design, it was found that all variables showed significant influence. In the second stage, using the Doehlert design with 5 variables, the optimal conditions were determined: pH 8.3, flow elution 5.5 mL min−1, buffer concentration 0.045 mol L−1, sample flow 5.5 mL L−1, and eluent solution (ascorbic acid 0.6% w/v in medium of hydrochloric acid at a final concentration of 0.06 mol L−1). The method was applied to the determination of uranium with a detection limit (LD) of 0.41 μg L−1 and quantification (LOQ) of 1.40 μg L−1, Relative standard deviation (RSD) 2.5 and 1.3% uranium concentration of 20 and 60 μg L−1, respectively. The factor of pre-concentration for the system is 46 for a sample volume of 50 mL. The accuracy was confirmed by the spike test. The procedure was applied for the determination of uranium in tap water, well water, and human consumption; the samples were collected in the municipalities of Caetite, Cruz das Almas, Itabuna, Aramari-BA, and seawater samples from Todos os Santos Bay. Uranium concentrations were found in the analyzed samples varying from 7.0 to 16.5 μg L−1.