Selective Determination of Cadmium in Water Using a Chromogenic Crown Ether in a Mixed Micellar Solution

The chromogenic crown ether N,N ‘-bis(2-hydroxy-5-nitrobenzyl)-4,13-diazadibenzo-18-crown-6 (CCE) has been solubilized in a mixed micellar solution of sodium dodecyl sulfate and cetyl pyridinium chloride and tested for the selective determination of heavy metal ions. The optical properties, acid−base equilibria, and metal ion binding capabilities of the micellar-solubilized CCE for Ba(II), Ca(II), Cd(II), Cu(II), Hg(II), Pb(II), and Sr(II) are reported. Results show that the micellar-solubilized CCE binds Hg(II) ∼ Cd(II) > Ca(II) > Sr(II), whereas the presence of Pb(II) and Ba(II) leads to precipitate formation. There was no detectable binding with Cu(II). Based on these results, a spectrophotometric determination for Cd(II) that utilizes chloride ions to mask Hg(II) has been devised and evaluated.