An improved method for rapid preconcentration and determination of bioactive trace metals in seawater using solid phase extraction and high resolution inductively coupled plasma mass spectrometry

Investigating how bioactive trace metals influence the cycling of macro-nutrients and carbon in oceanic and neritic environments is hindered by the labor-intensive and slow metal preconcentration methods currently available. We describe here a solid phase extraction method that rapidly preconcentrates a suite of bioactive trace metals from seawater. The ligand bis(2-hydroxyethyl) dithiocarbamate (HEDC) is added to seawater samples and forms neutrally-charged, but polar (water soluble) metal–ligand complexes with Fe, Co, Ni, Cu, Zn and Cd. These neutral complexes can be recovered onto polystyrene-based C-18 resin columns for subsequent elution with acidic methanol. Metals are recovered quantitatively between sample pH 5–8.5. Sample flow rates of >10 ml min−1 can be used, making it logistically possible to extract the larger sample volumes necessary for determining open ocean metal concentrations on conventional analytical instruments. Moreover, the method is well suited for developing flow extraction instrumentation for autonomous shipboard and in situ metal extractions and determinations. Here, we combine rapid seawater extractions with the measurement of bioactive metal concentrations by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). The low instrumental blank and high sensitivity and precision of HR-ICP-MS analyses combine to yield detection limits of ≤5 pM for the bioactive metals of interest.