Abstract
The PVC membrane of an ion-selective electrode (ISE) sensitive to dibasic phosphate ions (HPO4-ISE) has not been optimized for maximum selectivity, sensitivity, and useable ISE lifetime and further work was necessary to improve its performance. Two areas of investigation are reported here: include the parameters for the lipophilicity of the plasticizer compound used and the amount of cyclic polyamine ionophore incorporated in the PVC membrane. Six candidate plasticizers with a range of lipophilicity were evaluated for their effect on the useable lifetime, sensitivity, and selectivity of the ISE against 13 different anions. Selectivity was determined by a modified fixed interferent method, sensitivity was determined without interferents, and the usable lifetime evaluated at the elapsed time where 50% of the HPO4-ISE failed (L50). The results show that choosing a plasticizer that has a lipophilicity similar to the ionophore's results in the best selectivity and sensitivity and the longest L50.
Highlights
An ion-selective electrode sensitive to dibasic phosphate ions (HPO4-ISE) that is based on a cyclic polyamine for the ionophore has been previously described [1]
The purpose of this experiment was to investigate plasticizer lipophilicity (Klipo) and the amount of ionophore incorporated into the membrane as they relate to the useable lifetime, selectivity, and sensitivity of the HPO4-ISE
The selectivity, sensitivity, and service lifetime of the HPO4-ISE are greatly affected by the composition of the PVC membrane that supports the ionophore
Summary
An ion-selective electrode sensitive to dibasic phosphate ions (HPO4-ISE) that is based on a cyclic polyamine for the ionophore has been previously described [1]. When the lipophilicities of these two components are matched, I theorize that the plasticizer will be able to dissolve the maximum amount of ionophore, providing the most ion binding sites possible The purpose of this experiment was to investigate plasticizer lipophilicity (Klipo) and the amount of ionophore incorporated into the membrane as they relate to the useable lifetime, selectivity, and sensitivity of the HPO4-ISE. To investigate these effects the sensor membrane components were varied by amount of ionophore and the type of plasticizer used while maintaining the same polymer support (PVC). I hypothesize that there is an optimum plasticizer lipophilicity and ionophore concentration in the sensor membrane to yield the best sensitivity, selectivity, and useable lifetime for the HPO4-ISE
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