Journal Article Triple-quadrupole inductively coupled plasma-mass spectrometry with a high-efficiency sample introduction system for ultra-trace determination of 135Cs and 137Cs in environmental samples at femtogram levels

Zheng, Jian  ,  Cao, Liguo  ,  Tagami, Keiko  ,  Uchida, Shigeo

88 ( 17 )  , pp.8772 - 8779 , 2016-09 , ACS Publications
High yield fission products, 135Cs and 137Cs, have entered the environment as a result of anthropogenic nuclear activities. Analytical methods for ultra-trace measurement of 135Cs and 137Cs are required for environmental geochemical and nuclear forensics studies. Here we report a highly sensitive analytical method combining the APEX-Q desolvation sample introduction system with triple-quadrupole inductively coupled plasma-mass spectrometry (AEPX-ICP-MS/MS) for the determination of 135Cs and 135Cs/137Cs isotope ratio at femtogram levels. Using the APEX-ICP-MS/MS system, we introduced only selected ions into the collision/reaction cell to react with N2O, significantly reducing the isobaric interferences (135Ba+ and 137Ba+) and polyatomic interferences (95Mo40Ar+, 97Mo40Ar+, 119Sn16O+, and 121Sb16O+). Compared to the standard instrument setup of ICP-MS/MS, the APEX-ICP-MS/MS enables a 10-fold sensitivity increase. In addition, an effective chemical separation scheme consisting of AMP Cs-selective adsorption and two-stage ion-exchange chromatographic separation was developed to remove major matrix elements and interfering elements from environmental samples (10-40g). This separation method showed high decontamination factors (104-107) for major matrix elements (Al, Ca, K, Mg, Na and Si) and interfering elements (Ba, Mo, Sb and Sn). The high sensitivity of APEX-ICP-MS/MS and the effective removal sample matrix allowed reliable analysis of 135Cs and 137Cs isotopes with extremely low detection limits (0.002 pg mL-1). The accuracy and applicability of the APEX-ICP-MS/MS method was validated by analysis of seven standard reference materials (soils, sediment and plants). For the first time, ultra-trace determination of 135Cs and 135Cs/137Cs isotope ratio at global fallout source environmental samples was achieved with the ICP-MS technique.

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