Mass Discrimination Effect in Isotope Ratio Measurement of Barium by Triple-Quadrupole Inductively Coupled Plasma-Mass Spectrometry: Estimation of Mass Bias Coefficient for Isotopic Analysis of Radioactive Cesium Nuclides

Abstract

The mass discrimination effect in the isotope analyses of barium isotopes with natural abundance, from Ba-130 to Ba-138, was investigated by triple-quadrupole inductively coupled plasma-mass spectrometry (ICP-QQQ). The mass bias coefficients for Ba isotopes, denoted by ε(Ba), were determined from the slope of a linear relationship between the atomic mass differences and the ratios of ion count rates for a given isotope pair experimentally determined and calculated from natural abundances. The effect of the addition of a collision-reaction cell (CRC) gas such as helium, hydrogen, nitrous oxide, or carbon dioxide on ε(Ba) was examined. Large ε(Ba) values were observed in the case of He- or H2-CRC gas, and the values were from ＋0.8 to ＋1.7％ per atomic mass unit. On the other hand, ε(Ba) observed with CRC gasses containing N2O or CO2 was relatively small and below ＋0.3％ per atomic mass unit. In addition, the dependence of the energy discrimination potential (ED) applied between the CRC and the second quadrupole mass separator of ICP-QQQ on ε(Ba) was investigated. Finally, the analytical mass bias coefficient of the radioactive cesium nuclides 134Cs, 135Cs, and 137Cs, ε(Cs), was discussed for ε(Ba) in the same mass range as that of Ba isotopes.