DETERMINATION OF URANIUM AND THORIUM IN ALUMINUM WITH FLOW-INJECTION AND LASER ABLATION INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

In order to determine uranium and thorium at the sub-ng g-1 level in aluminium, the limit of detection (LOD) for continuous-flow nebulization inductively coupled plasma mass spectrometry (ICP-MS) is not sufficient, when a sample solution with the usual maximum concentration of 1 mg ml-1 is used. Therefore, two alternative sample introduction techniques have been used, flow injection (FI) and laser ablation (LA). With FI-ICP-MS the achievement of sub-ng g-1 detection limits is hampered by the presence of 'spikes'. Although these spikes are also present with LA, it is possible to obtain a 0.2 ng g-1 LOD for uranium and thorium. This LOD is achieved artificially, by rejecting all measurements containing spikes.