Potentiometric flow-injection determination of copper-complexing organic ligands with a copper-wire indicating electrode

The potentiometric response of a copper-wire indicator electrode in a flow-injection system with a phosphate-buffered carrier stream can be used to determine copper-complexing ligands; glycine, histidine, L-cysteine, EDTA, ethylenediamine, triethylenetetramine, dopamine and imidazole are discussed. The electrode response is shown to give peak potentials with a Nernstian relationship to total injected ligand concentration over limited ranges, depending on the stoichiometry, stability, and oxidation state of the copper complexes formed. Galvanostatic measurements showed that complex formation with Cu²⁺ or Cu⁺ or mixed species can be responsible for the response characteristics. The effects of adding 0.1 M sodium chloride to the carrier stream are generally beneficial, particularly in obtaining sharper responses. Detection limits can be improved to about 10^?5 M by adding about 10^?5 M Cu²⁺ to the carrier stream, but the linear range of Nernstian response is then narrow.