Comparison of Analytical Methods for the Determination of Uranium in Seawater Using Inductively Coupled Plasma Mass Spectrometry

Trace element determinations in seawater by inductively coupled plasma mass spectrometry are analytically challenging due to the typically very low concentrations of the trace elements and the potential interference of the salt matrix. In this study, we did a comparison for uranium analysis using inductively coupled plasma mass spectrometry (ICP-MS) of Sequim Bay seawater samples and three seawater certified reference materials (SLEW-3, CASS-5, and NASS-6) using eight different analytical approaches. The methods evaluated include the following: direct analysis, Fe/Pd reductive precipitation, off-line preconcentration using the actinide specific resin, UTEVA, standard addition calibration, on-line automated dilution using an external calibration with and without matrix matching, and on-line automated preconcentration using the seaFast preconcentration resin. The two methods which produced the most accurate results were the method of standard addition calibration and off-line preconcentration using the UTEVA resin, recovering uranium from a Sequim Bay seawater sample at 101 +/- 1.2% and 98 +/- 2.7%, respectively. The on-line preconcentration method and the automated dilution with matrix-matched calibration method also performed very well. The two least effective methods were the direct analysis and the Fe/Pd reductive precipitation method using sodium borohydride.