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

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 Yb3+ over the transition metal ions (Mn2+, Fe2+, Co2+, Ni2+, Zn2+), alkaline (Na+, K+) and alkaline earth metal (Mg2+, Ca2+, Sr2+, Ba2+) 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 (Gd3+, La3+ and Al3+) and Cu2+ to the Yb3+ response were significant for membrane 1, and the addition of anionic and cationic sites to membranes based on 1 decreased the selectivity to Yb3+ 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 Yb3+ 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.