Polymeric membrane electrodes for monohydrogen phosphate and sulfate

A zwitterionic bis(guanidinium) ionophore bearing an anionic closo-borane c luster (I) and a dihydrochloride analogue (2) are investigated in polymeric membrane ion-selective electrodes (ISEs), Both compounds have been previou sly shown to complex and selectively extract oxoanions. By systematic varyi ation of the kind and concentration of the ion-exchanger sites in the membr ane, the optimal performance with the so far best sulfate selectivity is fo und for ISE membranes based on the dihydrochloride, whereas those with the zwitterion analogue are shown to possess a reasonably good selectivity for monohydrogen phosphate.