DETERMINATION OF RARE-EARTH ELEMENTS IN SEAWATER BY INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

Shortly after sampling, rare earth elements (REEs) from 11.5 l of seawater were concentrated in 35 ml solutions by ion exchange chromatography on board the German research vessel "Sonne" using Chelex 100 chelating resin for preconcentration. Two millilitres of a 0.2 mug g-1 Lu spike was added to the seawater samples (i) for monitoring the chemical yield which was always found to vary between 85 and 112% (mean: 100 +/- 6) and (ii) as an internal standard. Rare earth elements have been determined by ICP-MS, with REE concentrations ranging from 100 (La) to 1 (Eu) pmol kg-1. La in blanks can be as high as 30 pmol kg-1, but blank concentrations for other REEs range between 0.5 and 0.01 pmol kg-1. The trend of the precision of relative response factors varies between 12% (La) and 4% (Yb). The accuracy is estimated to be about 10% with the exception of La and Ce. Methodology improvements are suggested.