Total dissolution of environmental samples for the determination of uranium and thorium by ICP-MS and alpha-particle spectrometry

A low-cost total dissolution method for accurate determination of uranium and thorium isotopes in environmental samples (soil and sediment) was introduced, optimised and validated. The method included alkaline fusion based on sodium hydroxide (NaOH) and sodium peroxide (Na2O2), followed by sequential extraction chromatography separation and measurements with ICP-MS or alpha-particle spectrometry. The overall chemical recoveries for U and Th for the entire procedure were about 80% and 90%, respectively. The U-238 contribution from partial dissolution of the nickel crucibles accounted for about 80% of the total background activity.