jeudi 4 juin 2015 à 16:00
In nuclear metrology, analysis of actinides present at ultra-trace concentrations in sediments (~mBq/kg) is carried out following a two-steps procedure : (i) the separation of these chemical elements after acid leaching by co-precipitation and/or chemical separation using chromatographic extraction resins  and (ii) the detection and quantification by α spectrometry . In general, the above procedure suffers from several drawbacks. It needs to use several resins, a long time consuming chemical separation steps and a relatively long analysis time by α spectrometry .
In this study, a simple method was developed to separate americium (Am) using single column extraction chromatography employing N, N, N’, N’-tetra-n-octyldiglycolamide (DGA) resin. The optimization of the new protocol was performed by inductively coupled plasma mass spectrometry (ICP-MS) and ionic chromatography (IC) using a synthetic solution doped with Eu, Th, U, Fe, Bi, Ca and real leaching solution doped with Eu.
The protocol has been optimized with U, Th and Eu (as chemical analogue of Am) from acid leaching solution (10 g of sediment per 50 mL of nitric acid 3M HNO3) with the following conditions: 2 g DGA, flow 1.5 mL / min using Ismatec mark pump).
The goal is to separate Am from the interfering elements (Bi, Pb, Tl, Hg, U) with minimal amount of major elements existing in the matrix (Ca, Na, Mg, K ....), the resin was washed with four acid solutions: 3M HNO3, 0.1M HNO3, 0.01M HNO3 and 0.1M HCl. Preliminary results obtained by ICP-MS showed the presence of a residual amount of uranium (1.7ppb) eluated with europium which may be explained by an incomplete separation of both elements or a contamination. As a consequence, an additional clean-up is needed. The collected fraction of Eu is evaporated to dryness using a closed evaporation system (Evapoclean, Analab), then the residue is dissolved in 6 mL of 3M HNO3 and loaded onto the same DGA column. The proposed chemical procedure was efficient to separate europium (Eu yield equal to 97.9±4%) with traces of uranium (33 ppt ‹‹0.5ppb). These results will allow us to determine concentrations of americium by HR-ICP-MS from samples in the Loire estuary.
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