Organic speciation of dissolved iron in estuarine and coastal waters at multiple analytical windows

Here we use cathodic stripping voltammetry with competitive ligand exchange (CLE–CSV) to determine the speciation of Fe in samples from the Mersey River estuary and Liverpool Bay in the presence of salicylaldoxime (SA). Multiple analytical windows (MAWs) were obtained by varying the concentration of SA. Data fittings from individual titrations were compared to simultaneous analysis of all windows using KINETEQL Multiwindow Solver (KMS) giving good agreement. Individual and MAW titrations agreed and demonstrated the presence of only one ligand dominating in all samples. The ligand concentration behaved non-conservatively with increasing salinity, and was in excess of the iron concentration throughout the salinity range tested. The ligand concentration co-varied with that of iron-binding humic substances (HS). Measurement of the composition of dissolved organic carbon (DOC) using 2-dimensional fluorescence scans indicated the presence of terrestrial as well as microbial sources of organic matter in the estuary. The fraction of HS in the DOC amounted between 21 and 46%.