Determination of low-level 135Cs and 135Cs/137Cs atomic ratios in large volume of seawater by chemical separation coupled with triple-quadrupole inductively coupled plasma mass spectrometry measurement for its oceanographic applications

Radioisotopes of cesium are powerful tracer for oceanographic studies. In this work, a novel method was developed for determination of ultra-low level Cs-135 and Cs-137 in seawater using triple-quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). Cesium was pre-concentrated from up to 45 L seawater samples using ammonium molybdophosphate (AMP) adsorption, following a selective leaching of cesium using Sr (OH)(2). The cesium was further purified from interfering elements using AMP-PAN and cation-exchange chromatography. Sr(OH)(2) leaching was found to be an effective approach for selective exchange of cesium from the AMP sorbent without dissolution, which avoids the problem of separation of huge amount of NH4+ and MoO42- in the following steps. The decontamination factors for barium and rubidium with the developed method were more than 4 x 10(7) and 800, respectively. The separated Cs-135 and Cs-137 were measured using ICP-MS/MS by employing N2O as reaction gas to further elimination of isobaric (i.e. Ba-135 and Ba-137) and polyatomic ions interferences. A detection limit of 1.5 x 10(-16) g L-1 for Cs-135 in seawater was achieved. The concentrations of Cs-135 in seawater from Baltic Sea, Danish straits and Roskilde Fjord were determined using the developed method to identify the sources of Cs-135, the water masses exchange in this region was investigated using Cs-135 and Cs-137.

Automated summary

A novel method was developed for determination of ultra-low level Cs-135 and Cs-137 in seawater, demonstrating successful pre-concentration and measurement of the isotopes. The method was used to investigate water masses exchange in the study region using Cs-135 and Cs-137.