Development of a fully automatic separation system coupled with online ICP-MS for measuring rare earth elements in seawater

Rare earth elements (REEs) are useful geological indicators of marine geochemistry. However, extremely low concentrations (sub-ng L-1) and high-salt matrices result in inefficient measurements. A fully automatic separation system (ELSPE-2 Precon) is used in the online determination of ultra-trace REEs in seawater using inductively coupled plasma mass spectrometry. This system mainly comprises three sections: (i) an auto-sampler (eas-2A) with 120 positions; (ii) a poly(styrene-divinylbenzene) resin column (Prin-Cen Col007) with iminodiacetic and ethylenediaminetriacetic acid functional groups to eliminate the high-salt matrix (e.g., Na, Ca, K, Mg, Al, Ba, Fe, Sr, P, and S) and preserve the target REEs; and (iii) a Trp002 cleanup column for the reduction of the reagent and procedural blank values. The detection limits (3 sigma) were in the range 0.002 (Dy)-0.097 ng L-1 (La), and the long-term reproducibility (8 h) was between 80% and 120% for all REEs in a 3.5% NaCl matrix solution. The accuracy of this method was verified using a seawater reference material (NASS-6), and the measured REE concentrations were consistent with those previously reported. The proposed online system was used to investigate coastal water samples with varying salinities from the Pearl River Estuary (Guangdong, China). Variations in the REE distribution patterns of different layers of seawater were observed, which could be due to the mixing of potentially light rare earth element-enriched bottom seawater. Moreover, a positive Gd anomaly in river water and seawater might be attributed to anthropogenic pollution from hospitals and the pharmaceutical industry.

Automated summary

This study introduces a fully automatic separation system for the online determination of ultra-trace rare earth elements (REEs) in seawater and applies it to coastal water samples from the Pearl River Estuary in China. The results show variations in the REE distribution patterns of different layers of seawater, potentially due to the mixing of light rare earth element-enriched bottom seawater. Additionally, a positive Gd anomaly in river water and seawater is observed, which may be attributed to anthropogenic pollution from hospitals and the pharmaceutical industry.