An efficient method for the separation of REEs from Ba for the accurate determination of REE content in Ba-rich samples by ICP-MS

Abstract

Barium (Ba) is a major element in many geological samples (e.g. barite/witherite-rich samples) and introduces serious oxide and hydroxide interferences during the analysis of rare earth elements (REEs) by ICP-MS. Hence, eliminating Ba interference is an indispensable step for accurate ICP-MS analysis of REEs. Though ion-exchange chromatography is widely used for REE purification, the tediousness, time consumption and high cost limit the application of this purification method. In this study, we developed a rapid and reliable separation method to eliminate Ba from geological samples for the precise measurement of REEs by ICP-MS. The new method was established based on the difference in solubility between Ba and REEs in concentrated nitric acid as barium nitrate (Ba(NO₃)₂) is almost insoluble, in contrast to REEs. The whole separation procedure could be completed in less than two hours and only consumed 1.5 mL 15 M nitric acid. The protocol resulted in acceptable procedural blanks (below 0.02 ng mL⁻¹), quantitative recovery (96–103%) of REEs, and limited Ba content (0.37 ± 0.14 μg mL⁻¹, (2SD, n = 50)) in the purified solution (50 mL), in which the interference effect could be eventually eliminated by mathematical correction during the ICP-MS analysis. The method was successfully applied to four natural barite-rich samples with BaSO₄ content ranging from 18.87 wt% to 42.41 wt%. Overall, this accurate and rapid method shows great potential for the precise determination of the REE content in Ba-rich samples by ICP-MS.