Direct determination of rare earth elements in natural water and digested sediment samples by inductively coupled plasma quadrupole mass spectrometry using collision cell

The present study is based on the use of a conventional quadrupole ICP-MS for determining directly rare earth elements (REEs) in both fresh or slightly saline waters and digested sediments. The development of a robust method using a collision reaction cell (different collision gases and fluxes have been tested) and kinetic energy discrimination is proposed for the accurate quantification of REEs without any mathematical corrections and preconcentration steps. The choice of He gas over H-2 and its flow in the collision reaction cell as well as the isotopes studied are thoroughly discussed with the aim of reducing drastically interferences. The exhaustive list of interferences (argides, chlorides, oxides, hydroxides, hydrides and doubly charged) has been investigated for the first time at different concentration levels, relevant with those found in environmental matrices based on the FORum of European Geological Surveys (FOREGS) database. The interference equivalent concentrations (IECs) have been determined and summarized. Although the impact of barium interferences onto europium and the impossibility to measure Sc have been pointed out, this method has been validated for all the other REEs in aquatic environmental matrices by studying the recoveries of spiked natural waters (5 commercially available mineral waters with dry residues ranging from 22 to 2,513 mg L-1 and a filtrated natural river water from Northern France) with relevant concentrations of REEs. Standard reference materials (Le. three waters (AQUA-1, SLRS-6 and SLEW-3) and four sediments (BCR-667, HISS-1, Metranal-1 and PACS-3)) were also analysed to ensure the robustness of the method.