Lanthanoid ion-selective solvent polymeric membrane electrode based on 1-phenyl-3-methyl-4-octadecanoyl-5-pyrazolone

Abstract

This work describes the potentiometric responses of liquid membranes incorporating a highly hydrophobic β-diketone-type chelating reagent, 1-phenyl-3-methyl-4-octadecanoyl-5-pyrazolone ( 1) to various metal ions. A membrane based on 1 without ionic additives (membrane 1) exhibited a selective potentiometric response to Yb 3+ over the transition metal ions (Mn 2+, Fe 2+, Co 2+, Ni 2+, Zn 2+), alkaline (Na +, K +) and alkaline earth metal (Mg 2+, Ca 2+, Sr 2+, Ba 2+) ions in a nearly Nernstian manner in the concentration range from ≈10 −6 to 10 −2 M at pH 5.5. The interferences of the other trivalent ions (Gd 3+, La 3+ and Al 3+) and Cu 2+ to the Yb 3+ response were significant for membrane 1, and the addition of anionic and cationic sites to membranes based on 1 decreased the selectivity to Yb 3+ over the other ions. This potentiometric selectivity correlates well to the separation selectivity in the solvent extraction of the metal ions with 4-acyl-5-pyrazolones into non-polar organic solutions. This correlation, and a decrease in the potentiometric responses to Yb 3+ at lower pH suggest that the potentiometric responses to the metal ions result from a decrease in the deprotonated ligands at the membrane interface due to the complex formation between the metal ions and the deprotonated ligands.