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

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. (author)