Moffett, J. W. Woods Hole Oceanographic Institution, jmoffett@whoi.edu
Saito, M. W. MIT-WHOI Joint Program, mak@mit.edu

 
ORGANIC COMPLEXATION OF COBALT IN THE SARGASSO SEA
 
We have performed Co titrations in seawater from the Sargasso Sea that show Co is predominantly complexed by organic ligands. We developed a highly sensitive assay for Co(II) using competitive ligand exchange cathodic stripping voltammetry with the competing ligand dimethylglyoxime (DMG). Sensitivity was enhanced using a nitrite catalyst and a rapid scan rate (10 V /s). We evaluated the method using model ligands, and showed that the analytical reagents were not initiating any Co(II)/Co(III) redox transformations in solution in a complimentary spectrophotometric investigation. In the Sargasso Sea samples, the ambient Co was strongly complexed by organic ligands. For a representative sample, total Co concentration = 23 pM, log K(conditional) = 16, ligand concentration = 40pM. As a result, free Co2+ is below 1e-16 M. The conditional stability constants are unusually high for Co(II), which typically forms much weaker complexes than Cu(II) or Fe(III). Such high values suggest that the ligand(s) detected may be biologically produced Co chelators. The implications of the data for the importance of Co as a micronutrient will be discussed.
 
Day: Wednesday, Feb. 3
Time: 04:45 - 05:00pm
Location: Sweeney Center
 
Code: SS28WE0445S