Low blank preconcentration technique for the determination of lead, copper, and cadmium in small-volume seawater samples by isotope dilution ICPMS

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 mu L 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 mu L 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.