A fast method for the simultaneous determination of 230Th, 234U and 235U with isotope dilution sector field ICP-MS

Abstract

A double focussing sector field ICP-MS with its variable resolution capability was used for the simultaneous measurement of Th and U isotopes to calculate excess ²³⁰Th and total U content in marine sediments. The necessary separation and concentration of Th and U from major and minor elements in the sediment samples was achieved by acid digestion followed by anion exchange. ICP-MS measurements were performed using a resolution of R = 4430 resulting in an abundance sensitivity of ²³⁰/₂₃₂ = 5 × 10^–7 which is small enough for the quantification of sediments with ²³⁰Th/²³²Th ratios as low as 10^–6. Using a microconcentric nebulizer (MCN-100), the lowest sample volume required for a single measurement was less than 200 µl. Analysis time was 80 s per sample. ²²⁹Th and ²³⁶U were used for quantification and as yield tracers. The overall uncertainty introduced by the entire separation procedure and the ICP-MS analyses was about 5% (95% confidence interval). The precision of each individual measurement was within 3% (2s).