UV digestion of seawater samples prior to the determination of copper using flow injection with chemiluminescence detection

A purpose built UV digestion system was successfully used for the breakdown of Cu complexing organic ligands in seawater samples, prior to total dissolved Cu determination using flow injection with chemiluminescence detection (FI-CL) and on-line micro-column preconcentration/matrix removal. Residual dissolved organic carbon (DOC) was quantified using a DOC analyser. Humic acid (1.8-7.2 mg l-1C) in ultra high purity (UHP) water was completely broken down within 4h in all batch experiments (125 and 400 W lamps; with and without 15 mM H2O2 and, as expected, was more rapid with the 400 W lamp, in the presence of H2O2, and for lower humic acid concentrations. UV digestion experiments with seawater showed that the residual DOC concentration after batch UV treatment (4h) was <0.08 mg l-1C compared with >0.32 mg l-1C after on-line irradiation (residence time 11.2 min). Therefore, the batch method was more efficient than on-line UV digestion at breaking down added humic acid and naturally present organic compounds in seawater. However, the release of Cu from metal complexing organic matter in seawater and estuarine water was the same using both on-line and batch UV digestion (sample irradiation residence time: 5.6 min and 8h, respectively). UV digestion is, therefore, a contamination-free approach for seawater pretreatment prior to micro-column preconcentration and FI-CL determination of total dissolved Cu and should also be applicable to the selective determination of the total dissolved fractions of other trace metals in seawater (e.g. Co, Fe, Mn). © 2001 Elsevier Science B.V. All rights reserved