Stepwise extraction of two lead ions with a single molecule of calix[4]arene tetracarboxylic acid

Solvent extraction of metal ions including lead(II) with calix[4]arene tetr acarboxylic acid was investigated. The selective extraction behavior for le ad ion was examined in detail. Two lead ions were found to be extracted wit h a single molecule of calix[4]arene derivative from the experimental resul ts by Job's method, a loading test, and slope analysis of lead concentratio n dependency. The extraction data and the chemical shift of H-1-NMR for the extractant caused by the complexation with lead supports the conclusion th at two lead ions are extracted stepwise. The extraction behavior of lead io n with the monomeric derivative was also investigated to compare that with the cyclic tetramer. The stoichiometry of the complex formed by the monomer ic derivative and lead was found to be 2:1. Separation and preconcentration of a trace amount of lead ion from a large excess of zinc ion was also exa mined from an analytical point of view. The cyclic tetramer could achieve a successful separation of a trace amount of lead ion from an excess amount of zinc ion. Stripping of loaded lead from the cyclic tetramer ion was also investigated. Complete stripping could be achieved by nitric acid at a con centration greater than 3 mol dm(-3). (C) 1999 Elsevier Science B.V. All ri ghts reserved.