Onsite chelate resin solid-phase extraction of rare earth elements in natural water samples: its implication for studying past redox changes by inorganic geochemistry

Rare earth element (REE) patterns in natural water and geological samples provide information on previous changes in environmental conditions, such as redox changes and material cycles; however, quantitative analysis of REEs in these samples is complicated by the relatively low contents of REEs in such samples as well as mass interference from (BaO)-Ba-135-O-16 and (BaO)-Ba-137-O-16 in inductively coupled plasma mass spectrometry (ICP-MS) analyses. In this study, onsite solid-phase extraction and preconcentration methods for REEs using an iminobisacetic acid-ethylenediaminetriacetic acid chelate resin (Nobias Chelate PA1, Hitachi High-Tech Fielding) were adopted for the analyses. Standard reference materials (SPS-SW1 artificial surface water) and natural ground water and spring water samples were used to evaluate the methods. Using the chelate resin, background levels of REEs were found to be less than 0.3 ng L-1 and recovery rates (REEs, 1 ng L-1) were 97.9-106.7% for the artificial surface water. Ba contents were lower than the detection limit after extraction. Additionally, duplicate analyses were performed to check the reproducibility of the onsite extraction. The REE patterns in the natural water samples were in good agreement with those obtained using a previous method (the interference calibration method without solid-phase extraction). Therefore, onsite solid-phase extraction using the chelate resin was demonstrated to be a rapid and simple preparation technique for REE analyses.