Applications of voltammetry in studies of the speciation of heavy metals by organic chelators in sea water

Abstract

Abstract The general conditions for the speciation of zinc and cadmium in sea water by nonlabile chelate species formed with components of dissolved organic matter (DOM) have been investigated using NTA as a model ligand with defined coordination chemical properties. The specific side effects of the salinity components on the chelation have been determined. The application of the very sensitive differential pulse anodic stripping voltammetry (DPASV) at the hanging mercury drop electrode (EMUE) enabled measurements at rather realistic overall trace metal levels of 3 × 10−9 M Cd(II) and 3.2 × 10−8 M Zn(II). Their chelation behaviour is compared with that of Pb(II). General conclusions on the chelation by DOM‐components of all three heavy metals in natural waters emerge. The with NTA obtained data establish a basis for prognostic estimates on the ligand concentrations required for the formation of chelates with medium stability, i.e. with common'conditional stability constants in the range of 1g K between 8 and 12. From these findings it can be concluded that with respect to the restricted DOM‐levels in major parts of the sea a number of DOM‐components can be ruled out as candidates for significant effects on the speciation of Cd(II), Zn(II) and Pb(II). In terms of methodology the study features the particular suitability of voltammetry for the investigation of heavy metal speciation in natural waters.