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A simple low-blank method is described for the analysis of Pb, Cu, and Cd in seawater using Mg[(OH).sub.2] coprecipitation and isotope dilution inductively coupled plasma mass spectrometry (ICPMS). Here, 20-40 [[micro]liter] 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).sub.2] precipitate dissolved in 100 [[micro]liter] of 5% HN[O.sub.3] 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.

A new isotope dilution inductively coupled plasma mass spectrometry (ICPMS) method is developed to determine picomolar concentrations of titanium (Ti) in seawater. The method applies Mg(OH) 2 coprecipitation to concentrate Ti from seawater, and uses a new 49 Ti- 47 Ti isotope dilution to eliminate the need for separating Ti from seawater Ca, resulting in an isobaric interference-free analysis by high-resolution multicollector ICPMS. The method uses a 1.8 mL seawater sample with a detection limit of 1.6 pmol L -1 that is determined mainly by Ti contamination during sample preparation rather than by ICPMS sensitivity, instrumental Ti background, or isobaric interferences. An oceanographically consistent vertical profile of dissolved Ti in the Sargasso Sea near Bermuda is measured with this method.