Accurate determination of ultra-trace impurities, including europium, in ultra-pure barium carbonate materials through inductively coupled plasma–tandem mass spectrometry

Impurities, especially ultra-trace europium (Eu), in ultra-pure barium carbonate materials were accurately determined through inductively coupled plasma–tandem mass spectrometry (ICP-MS/MS). Two reaction modes, namely, mass shift (with O₂ as reaction gas) and on-mass modes(with NH₃/He and He as reaction gases), were extensively investigated using Eu⁺ as target analyte. The use of Eu⁺ → EuO₂⁺, instead of Eu⁺ → EuO⁺, as ion pairs in mass shift mode eliminated polyatomic interferences based on Ba matrix ions (¹³⁵Ba¹⁶O₂⁺ on ¹⁵¹Eu¹⁶O⁺ and ¹³⁷Ba¹⁶O₂⁺ on ¹⁵³Eu¹⁶O⁺). This procedure exhibited enhanced sensitivity and selectivity. When the ICP-MS/MS was operated in NH₃ on-mass mode, Eu⁺ can be determined in its original mass in interference-free conditions because NH₃ did not react with Eu⁺ but with BaO⁺ to form a neutral product (BaO). The two reaction modes, especially NH₃ on mass mode, were validated to be accurate because their resultant isotope ratios of ¹⁵³Eu/¹⁵¹Eu matched well with that of the natural abundance ratio. The proposed ICP-MS/MS method is a sensitive technique with a limit of detection as low as 2.0 ng L⁻¹ for ¹⁵³Eu⁺. Compared with conventional single-quadrupole (SQ) ICP-MS, both NH₃ on-mass mode and O₂ mass shift mode in ICP-MS/MS can be used to accurately determine Eu⁺ in ultra-pure BaCO₃ materials. The detected concentration of Eu⁺ was 4.0 ng L⁻¹ to 15 ng L⁻¹, with spiked recoveries ranging from 100%–110%. ICP-MS/MS was also used to eliminate polyatomic interferences, particularly Ba-based interferences, prior to measurement of Gd and Sm. Impurities, including Na, Mg, Al, K, Mn, Fe, Cr, Sr, and Cs, in ultra-pure BaCO₃ materials were also determined using ICP-MS/MS in conventional SQ mode. - Highlights: • Novel method for the interference-free determination of Eu at ultra-trace levels in the ultra-pure BaCO₃ materials • Novel method based on EuO₂⁺ reaction product ion formation using recently introduced ICP-MS/MS instrumentation • Lowest limits of detection obtained using quadrupole-based instrumentation for Eu with both on mass and mass shift modes