Method for ultra-trace cesium isotope ratio measurements from environmental samples using thermal ionization mass spectrometry

Cs-135/Cs-137 isotope ratios can provide the age, origin and history of environmental Cs contamination. Relatively high precision Cs-135/Cs-137 isotope ratio measurements from samples containing femtogram quantities of (CS)-C-137 are needed to accurately track contamination resuspension and redistribution following environmental Cs-137 releases; however, mass spectrometric analyses of environmental samples are limited by the large quantities of ionization inhibitors and isobaric interferences which are present at relatively high concentrations in the environment. We report a new approach for Cs purification from environmental samples. An initial ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) column provides a robust, selective method for extracting Cs under a wide variety of sample matrices and mass loads. Application of a novel cation exchange separation approach using AMP-PAN results in more than two orders of magnitude greater Cs/Rb separation factors than commercially available strong cation exchangers. Final sample purification using a microcation column (AG50W resin) enables consistent 2-4% (2 sigma) measurement errors for samples containing 3-6000 fg Cs-137, representing the highest precision (CS)-C-135/Cs-137 ratio measurements currently reported for soil samples at the femtogram level. Published by Elsevier B.V.