DETERMINATION OF THE MERCURY COMPLEXATION CAPACITY OF NATURAL-WATERS BY ANODIC-STRIPPING VOLTAMMETRY

The complexation of mercury by dissolved organic :matter (DOM) in natu ral waters was investigated using Osteryoung square wave anodic stripp ing voltammetry (OSWASV). The method employed a gold disc electrode an d utilised medium exchange (0.1 M perchloric acid/2.5 mM hydrochloric acid) to avoid interferences during the stripping step. The limit of d etection (3 sigma) was 0.11 nM (22 ng l(-1)) and the relative standard deviation at a mercury concentration of 5.0 nM was 2.8%. Mercury comp lexation capacities were determined, on a range of fresh and saline wa ter samples. In all samples, ligand concentrations were greatly in exc ess of dissolved mercury concentrations and ranged from 1.35 to 4.47 n M. Log conditional stability constants of the mercury-DOM complexes we re in the range 9.7-10.8. The results suggest that the speciation of m ercury in natural waters is dominated by complexation with natural org anic matter.