New prospects for plutonium speciation - CE-RIMS and CE-DAD-ICP-MS

Full text of publication follows: In the last years, capillary electrophoresis (CE)-ICP-MS has been applied successfully for the speciation of plutonium and neptunium [1] in aqueous solutions, especially in groundwater samples. To achieve lower detection limits and to determine complexing agents, two detection methods, namely RIMS and DAD, coupled with the separation technique CE are under investigation. A detection limit of 20 ppb was found for plutonium with an ICP-QMS, whereas with the coupling with a sector field ICP-HRMS 100 ppt could be detected. The off-line coupling of CE to the very sensitive resonance ionisation mass spectrometry (RIMS) with an absolute detection limit of 106 atoms gives new options. For this, a sample is injected into the CE-capillary and the separated oxidation states of Pu(III), Pu(VI/V) and Pu(IV) are collected in different fractions from which filaments are prepared for the RIMS measurements [2]. The migration times of the different Pu species have been previously calibrated by means of the CE-ICP-MS. The second innovation is the combination of a diode array detector (DAD) with the CE-ICP-MS. In addition to the information on the metal ions detected by the ICP-MS, the DAD can detect complexing agents like humic acid and also the electro-osmotic flow (EOF) by a suitable marker like acetone. This is necessary for internal standardisation of the migration times of the species in the capillary. By applying both detection methods, it is possible to determine in an anionic run free humic acid, humate complexed metal ions, and other (humate free) anionic metal species. In a cationic run, the free metal ions can be detected. This will enable the determination of complex formation constants. Related results will be presented at the conference. [1] B. Kuczewski et al.: Analytical Chemistry, 2003, 75, 6769-6774. [2] N. Trautmann et al.: Analytical and Bioanalytical Chemistry, 2004, 378, 348-355. (authors)