Construction and Characterization of Erbium(III) Porphyrin-Based Polymer Membrane Electrodes for the Determination of Benzoate Anions

Date of Graduation

Summer 2005


Master of Science in Chemistry


Chemistry and Biochemistry

Committee Chair

Erich Steinle


The need to quickly and accurately determine low concentrations of anions has promoted the development of ion-selective electrodes (ISEs) as potentiometric sensors. ISEs that respond to anions such as chloride, fluoride, salicylate and nitrate have been developed. Each ISE is dependent on a compound known as an ionophore which specifically binds the target anion. This work involved examining Erbium(III) porphyrins as possible ionophores for ISEs. A plasticized polyvinyl chloride (PVC) membrane doped with Erbium(III) porphyrin was mounted on electrode bodies and used to determine potentiometric responses to a broad range of anions over different concentration values. Preliminary results from the Erbium(III) porphyrin-based ISEs demonstrated unique selectivity patterns that are different from commercially-available ISEs. The effect of adding lipophilic ionic sites (tridodecylmethyl ammonium chloride, TDMAC) to these membranes was also examined and showed enhanced selectivity to benzoate anion. Different amounts of TDMAC incorporated in the membrane indicated improvement in potentiometric enhancement of the ISEs response to benzoate. Low pH levels are shown to decrease potentiometric responses of the ISEs to benzoate anions while higher pH level was seen to enhance them. The ISEs were optimized to respond to benzoate and eliminate interferences. Results from the ISEs were compared to those measured with high performance liquid chromatography (HPLC), a method commonly used for analysis of benzoate anions. Possible applications of these ISEs, especially in the industrial field, were demonstrated.


ion-selective electrode, potentiometric sensor, erbium(III) porphyrin, additive, benzoate, optimization, interference

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© Joseph K. Mbugua