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

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 Th-230 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 x 10(-7) which is small enough for the quantification of sediments with Th-230/Th-232 ratios as Tow as 10(-6). Using a microconcentric nebulizer (MCN-100), the lowest sample volume required for a single measurement was less than 200 yl. Analysis time was 80 s per sample. Th-229 and- U-236 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).