Lower Rim Substituted p‐tert ‐Butyl‐Calix[4]arene. Part 15. Pb(II)‐Ion‐Selective Electrodes Based on p‐tert ‐Butyl‐calix[4]arene Thioamides

Tetrasubstituted p‐tert‐ butylcalix[4]arene‐thioamides ( 1 – 5 ) were applied as ionophores in ion‐selective membrane electrodes (ISE) and were tested towards Pb‐selectivity. The selectivity coefficients of the electrodes were determined. The tertiary calix[4]thioamides ( 1, 2 ) show remarkable selectivity for Pb(II) cations when compared with respectable calix[4]amides. The electrode membranes with those ligands are stable, the Pb‐characteristics are close to nernstian within a wide linear range (−log c =6–1). Compounds 3 – 5 , the secondary calix[4]thioamides form less stable electrode membranes. Complex formation constants of the ligands 1, 2, 3 and 5 with Pb(II) and some most interfering ions were determined.