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

A double focussing sector field ICP-MS with its variable resolution capabil ity was used for the simultaneous measurement of Th and U isotopes to calcu late excess Th-230 and total U content in marine sediments. The necessary s eparation and concentration of Th and U from major and minor elements in th e sediment samples was achieved by acid digestion followed by anion exchang e. ICP-MS measurements were performed using a resolution of R = 4430 result ing in an abundance sensitivity of 230/232 = 5 x 10(-7) which is small enou gh 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 volu me required for a single measurement was less than 200 yl. Analysis time wa s 80 s per sample. Th-229 and- U-236 were used for quantification and as yi eld tracers. The overall uncertainty introduced by the entire separation pr ocedure and the ICP-MS analyses was about 5% (95% confidence interval). The precision of each individual measurement was within 3% (2s).