Development of an analytical system for speciation of trace metals using catalytic reactions

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1.Determinable reactive speciesA catalytic spectrophotometric determination method for speciation of copper was developed using a copper-catalyzed oxidation of ascorbic acid in the presence of o-phenylenediamine. Reactive species of copper were characterized by a complexation study of oxalato-copper species. The study revealed that the reactive copper species were Cu^<2+> and Cu^<II>L_n (n≦2 for an unidentate and n=1 for bidentate ligand (L)).2.Instrumentation of flow system for speciation analysisFor determination of reactive copper, PTFE tube used for the flow system adsorbs copper on its inner wall and seriously interfered with the determination. A manifold with individual flow lines for each reagent and sample solutions and a carrier solution with aluminum effectively inhibited the adsorption of copper. Copper was determined with an error of 1 ng/ml and a sampling frequency of 6 samples/h. A flow line for fluorometric determination of humic substances was incorporated with the flow system for copper. As humic acid, humic substances were simultaneously determined up to 200 ng/ml with an error of 10 ng/ml.3.ApplicationThe proposed analytical system was applied to the speciation of copper and humic acid in the presence of aluminum in an artificial river water sample containing copper(II), humic acid, iron(III) and silicate. Decrease of concentrations of reactive copper and humic acid suggested the formation of humic aggregates containing copper. The effect of fluoride ions in the presence of aluminum was also studied for the same artificial sample.