Smart sensory materials for divalent cations: A dithizone immobilized membrane for optical analysis

An optode for Cu(II), Cd(II), Zn(II) and Hg(II) sensing has been designed by immobilization of dithizone on a
triacetylcellulose membrane (mem-DTZ). The sorption of the metal ions on the mem-DTZ has been
thoroughly characterized, in particular sorption kinetics, sorption isotherms and profiles as a function of
the pH have been studied. Methods to assess the concentrations of the cations, both individually and in a
mixture, in unknown samples, have been developed. In particular, UV-vis spectra and digital information
of pictures taken by using a common desktop scanner, of the mem-DTZ sensor after equilibration with
different solutions, were acquired and they were correlated with the concentration of the metal ions in
solutions. For the single analyte determination, the RGB parameters of the pictures were subjected to
Principal Component Analysis (PCA); otherwise the UV-vis spectra of a mixture of two cations were elaborated
by Partial Least Squares (PLS) Regression. The membrane responds to the divalent cations by
changing colour reversibly. The response time of the mem-DTZ is about 1 h for Cd(II), Hg(II) and Zn(II), but
longer for Cu(II): more than 10 h are required. The linear interval is in the range of about 10−7 to 10−5 M
for all metal ions. The limit of detection (LOD) is around 10−6 M for Cu(II), Cd(II) and Hg(II); for Zn(II) a lower
LOD of 10−7 M is obtained. The applicability of mem-DTZ to real samples has been proved by analysis
of the four metal cations in a certificate material (Sewage Sludge CC136A), white wine, and drinking
water samples.