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Environmental context Metal contamination of seawater can present severe environmental problems owing to the high toxicity of metals and their persistence in the environment. This study explores the possibility of analysing lead in seawater media using two recently developed electrochemical methods. The methods are shown to be very useful tools to monitor the behaviour and fate of lead and other metals in seawater. Abstract The speciation of PbII in synthetic and real seawater is studied by absence of gradients and Nernstian equilibrium stripping (AGNES) and stripping chronopotentiometry at scanned deposition potential (SSCP). The usefulness of the combination of both techniques in the same electrochemical cell for trace metal speciation analysis is assessed at different pH values (2.7, 5.0, 6.0, 7.0 and 8.6). The AGNES (free metal ion concentrations) and SSCP (stability constants) results for synthetic seawater agree reasonably with each other and with the theoretical predictions of the software Visual MINTEQ 3.0. This is also true for real seawater media below pH 7.0. Because of the influence of natural organic matter (2.01mgL–1 total organic carbon) in the real seawater at pH 7.0 and 8.6 the SSCP signal showed that the PbII complexes became less labile and were formed by chemically heterogeneous ligands. At these pH values, free metal concentrations determined by AGNES agreed with concentrations predicted by Visual MINTEQ using a generic fulvic acid concentration.

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A simple technique for the isolation, concentration and matrix simplification of Cu(II) ion in natural waters is proposed. This method has been developed using poly(styrene-divinylbenzene) membrane disks modified with the synthesized ligand pyridoxal salicyloylhydrazone (PSH). The retained ions on the disks were eluted with 10 mL 1 mol L(-1) HNO(3) and measured by flame atomic absorption spectrometry at 324.8 nm. The influence of pH, amount of ligand, type and amount of eluent for the stripping of copper ion from the membrane over extraction efficiency were evaluated. Extraction efficiencies >99% were obtained by elution of the disks with minimal amount of solvent with a preconcentration factor up to 100. The precision of the method for 10 replicate measurements of aqueous solutions containing 40 μg L(-1) Cu(II) was 1.5% at significance level of 95%. The breakthrough volume for 5 μg of Cu(II) was found to be 1000 mL and the detection limit of the method was 4 ng L(-1) of metal ion. The present method was successfully applied to the extraction and determination of copper in lake and sea waters.