Direct determination of rare earth elements in natural water samples by inductively coupled plasma tandem quadrupole mass spectrometry with oxygen as the reaction gas for separating spectral interferences

Abstract

Rare earth elements (REEs) were measured by inductively coupled plasma tandem quadrupole mass spectrometer (ICP-MS/MS) with oxygen as the reaction gas to achieve monoxide ions of REEs for separating from spectral interferences. Production rates of REEs' monoxide ions were improved by optimization of the octopole bias voltage for the reaction cell of the ICP-MS/MS. The optimized operating conditions provided instrumental detection limits from 0.004 pg mL−1 of Er to 0.26 pg mL−1 of Nd and permitted the direct determination of REEs in natural river water and lake water samples. Analytical results of REEs in a certified reference material (SLRS-4) were in coincidence with reported values, which confirmed the validity of the method. Compiled values for REEs in SLRS-4 were calculated based on the present results and reported data. Isotope dilution was applied to the determination of Gd, Dy, Er, and Yb in SLRS-4, which results confirmed the accuracy of the compiled values. REEs in multiple river water samples and a lake water sample were determined, covering a range from 0.24 pg mL−1 of Tm to 130.9 pg mL−1 of Ce. The results of REEs in natural water samples were evaluated by normalization to the concentrations of REEs in post Archean Australian shale (PAAS).