Analysis of rare earth elements in seawater by inductively coupled plasma mass spectrometry after pre-concentration using TSK™-HD-MW-CNTs (highly dispersive multi-walled carbon nanotubes)

This study aimed to identify easy-to-use multi-walled carbon nanotubes (MW-CNTs) having a high capacity to adsorb metals and thereby expand the usability of these materials as a solid-phase adsorbent for the analysis of trace metals in seawater. High-dispersion-type MW-CNTs had the highest metal binding capacity (70.8±5.1 mg/g for La) after a strong acid oxidation procedure, possibly because the high dispersibility resulted in a more complete reaction than with highly crystalline types. Because the high-dispersion-type MW-CNTs leaked from a conventional column, they were attached to polymer beads (TSK™) (pore diameter about 20 μm). Flow rate, pH, and volume of the seawater sample, as well as eluent type and volume, were optimized to obtain 0.01–0.16 pg/mL detection limits for rare earth elements (REEs). In addition, normalized patterns for samples collected from the East Sea showed characteristic features of REEs in seawater, i.e., a negative Ce anomaly, low atomic number REE (LREE) depletion, and high atomic number REE (HREE) enrichment.