The use of chemiluminescence and ligand competition with EDTA to measure copper concentration and speciation in seawater

• Published in: Marine chemistry 1991-12, Vol.36 (1), p.137-163
• Main Authors: Sunda, William G., Huntsman, Susan A.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Geochemistry; Geochemistry: general, methodology, regional studies; Marine; Mineralogy; Physical and chemical properties of sea water; Physics of the oceans; Silicates; Water geochemistry
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/S0304-4203(09)90059-7

A batch chemiluminescence method for measurement of copper in seawater was developed from an existing flow injection technique. The method involved the reaction of copper in the sample with 1,10-phenanthroline, and subsequent release of photons from the oxidation of copper(II)-phenan-throline chelates by H 2O 2 at alkaline pH. The method was extremely sensitive with a detection limit in the range of 0.05–for 200 μl samples. Because of its sensitivity, it could be used to measure copper directly in seawater without a preconcentration step. To measure total copper, samples had to be acidified to pH 2 and stored for weeks to months (and in some cases also photo-oxidized by UV light) to release copper from kinetically inert species. Total copper concentrations measured by the chemiluminescence method in natural seawater agreed well with those obtained by more traditional methods. The chemiluminescence method was sensitive to copper speciation due to the slow dissociation of many bound copper species. This property was utilized to develop a ligand competition technique for measurement of free cupric ion concentrations. The method involved additions of EDTA and copper to seawater and was based on the lack of detectability of CuEDTA chelates by the chemiluminescence method. Free cupric ion concentrations measured by this method ranged from 10 −12.9 M for a relatively clean estuarine sample containing 5 nM total dissolved copper to 10 −10.9 M for a sample from a polluted harbor which contained 38 nM copper. Cupric ion concentrations measured by the new method were in good agreement with those measured in the same samples by a previously published method: EDTA competition combined with copper adsorption on to C 18 Sep—Pak cartridges. Copper was found to be heavily (>99%) complexed by natural organic ligands in both shelf and estuarine water samples and the concentrations of these ligands generally increased with dissolved copper concentration and decreasing sample salinity. These results agree with those of several previous studies.