Luminescent hexanuclear Cu(I)-cluster for the selective determination of copper

For the first time, the formation of a luminescent hexanuclear cluster has been used for the selective determination of copper. In aqueous solutions, the non-luminescent ligand N-ethyl-N′-methylsulfonylthiourea (EMT) forms an intensely red luminescent hexanuclear Cu(I)-cluster with an emission maximum at 663 nm only with Cu(II) ions. The intensity of the luminescence is proportional to the Cu(II) concentration and allows for selective Cu determinations in the μg l⁻¹-range. Ubiquitous metal ions such as Fe(III), Al(III), Ca(II), Mg(II), and alkaline metal ions, as well as other heavy metal ions, e.g. Co(II), Ni(II), Zn(II), Cd(II), Hg(II), and Pb(II) are tolerated in concentrations up to 50 mg l⁻¹. The detection limit for Cu(II) in aqueous solution, calculated according to Funk et al. [Qualitätssicherung in der Analytischen Chemie, Verlag Chemie, Weinheim, 1992], is 113 μg l⁻¹. The cluster formation has been used for the quantitative analysis of copper in tap water and in industrial water, as well as for the localization of copper adsorbed by activated-sludge flocs.