Low Blank Preconcentration Technique for the Determination of Lead, Copper, and Cadmium in Small-Volume Seawater Samples by Isotope Dilution ICPMS

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Abstract
A simple low-blank method is described for the analysis of Pb, Cu, and Cd in seawater using Mg(OH)2 coprecipitation and isotope dilution inductively coupled plasma mass spectrometry (ICPMS). Here, 20−40 μL of 9 M aqueous NH3 is mixed into a 1.3 mL seawater sample spiked with enriched isotopes of Pb, Cu, and Cd. After centrifugation, the supernatant is discarded and the Mg(OH)2 precipitate dissolved in 100 μL of 5% HNO3 for ICPMS analysis. This method is simple, accurate, and precise, with detection limits of Pb = 1.3 pM, Cu = 39 pM, and Cd = 5.0 pM and blanks of Pb = 0.62 pM, Cu = 27 pM, and Cd = 6.0 pM. The method is demonstrated by oceanographically consistent profiles of these trace metals at an ocean station in the eastern North Atlantic.