Amide and Acyl‐Hydrazine Functionalized Calix[4]arenes as Carriers for Hydrogen Phosphate Selective Electrodes

Anion‐selective solvent polymeric membrane based on hydrogen bond‐forming, neutral ionophores with amide or acyl‐hydrazine groups are described. The use of the two calix4]arenes results in anion‐selective electrodes with a selectivity for phosphate. The electrodes of the optimum characteristic have the composition of 1 wt% ionophore, 66 wt% o‐NPOE, 33 wt% poly (vinyl chloride) (PVC) and TDMACl (15 or 30 mol% relative to the ionophore 1 and 2 , respectively). The optimized membrane electrodes show Nernstian responses towards monohydrogen phosphate (?29.1 and ?29.3 mV/decade) based on ionophore 1 and 2 , respectively, in a wide concentration range (1.0×10^?5 to 1.0×10^?2 or 1.0×10^?5 to 1.0×10^?1 M). The selectivity coefficients are determined with the fixed interference method and the activity ratio method. The electrodes display an anti‐Hofmeister series selectivity pattern and highly selective for HPO₄^2? over Cl^?, Br^?, CH₃COO^?, NO₃^? and SO₄^2?. The lifetime of the electrodes is at least 1 month and their response time is found to be 25 s. The proposed sensors could be put to analytical use both by direct potentiometry as well as potentiometric titration.