Determination of Ambient Dissolved Chemical Speciation via Kinetics and Pseudovoltammetry

Dissolved chemical speciation of metals in natural waters encompasses a wide range of inorganic and organic compounds including metal organic ligand complexes. Because of the different filters used, “dissolved” speciation can range from simple metal-ligand complexes with an average size of about 1 nm (mass of <3 kilo-daltons) to nanoparticles of 1 to 100 nm to colloidal forms that are 10 to 200-400 nm in size. In this presentation, I discuss some of the types of compounds, complexes and (nano)particles that are found in marine waters and these size classes (including waters emanating from hydrothermal vents using Fe, Zn, Cu as elements of interest). The classification of a chemical species as “truly dissolved” is not favored terminology. Unfortunately, metal-ligand CLE-CSV titrations do not give good information on the actual chemical species present; however, pseudovoltammetry does for Zn, Cu, Cd and Pb. It is more important to understand the reactivity of a given chemical species, which is determined by kinetics experiments. Examples of the latter that will be demonstrated include ligand exchange, metal exchange and the half-life of redox species.