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

Solvent extraction of metal ions including lead(II) with calix[4]arene tetracarboxylic acid was investigated. The selective extraction behavior for lead ion was examined in detail. Two lead ions were found to be extracted with a single molecule of calix[4]arene derivative from the experimental results by Jobʹs method, a loading test, and slope analysis of lead concentration dependency. The extraction data and the chemical shift of 1H-NMR for the extractant caused by the complexation with lead supports the conclusion that two lead ions are extracted stepwise. The extraction behavior of lead ion with the monomeric derivative was also investigated to compare that with the cyclic tetramer. The stoichiometry of the complex formed by the monomeric 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 examined 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 concentration greater than 3 mol dm−3.