Determination of rare earth elements in environmental samples with high concentrations of barium by quadrupole inductively coupled plasma mass spectrometry

Abstract

This paper proposes a new method of sample preparation for the determination of rare earth elements (REE) by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) in challenging environmental samples with high Ba concentrations. The method consists in adding 10% (v/v) sulfuric acid to the wet sample digest, obtained after acid decomposition in an open system, in order to precipitate and separate BaSO4. The removal of BaO interference in Eu isotopes was efficient for Ba concentrations in solution higher than 0.1 mg L−1. The methodology was applied to asphalt pavement and the crushed stone used to produce it. Accuracy was assessed using two certified materials, NIST 688 Standard Reference Material of basalt rock and Geological Survey G2 granite, resulting in acceptable recoveries. Additionally, all samples were decomposed by fusion, and the concentrations of major elements and Eu were determined by inductively coupled plasma optical emission spectrometry (ICP OES). Eu results were in agreement with the proposed methodology, and limits of detection for REE varied from 0.003 mg L−1 (Lu) to 0.010 mg L−1 (Gd). The NASC normalized profiles of REE in the crushed stone showed a positive Eu anomaly, that was not observed in the asphalt sample. As well, the latter was enriched in heavy REE (Tb-Lu), suggesting a loss of carbonatite minerals, consequently to the weathering of the pavement.