Low level detection of 135Cs and 137Cs in environmental samples by ICP-MS

The measurement of fission product cesium isotopes Cs-135 and Cs-137 at low femtogram (fg) 10(-15) levels in ground water by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is reported. To eliminate the natural barium isobaric interference on the cesium isotopes, in-line chromatographic separation of the cesium from barium was performed followed by high sensitivity ICP-MS analysis. A high efficiency desolvating nebulizer system was employed to maximize ICP-MS sensitivity similar to 10 cps/fg. The three sigma detection limit for Cs-135 was 2 fg/mL (0.1 mu Bq/mL) and for Cs-137 0.9 fg/mL (0.0027 Bq/mL) measured from the standard with analysis time of less than 30 min/sample. Cesium detection and 135/137 isotope ratio measurement at very low femtogram levels using this method in a spiked ground water matrix is also demonstrated.