Development of anion selective polymer membrane electrodes based on lutetium(III) porphyrins

Liquid polymer membrane electrodes based on lutetium(III) porphyrins are examined as anion-selective electrodes. The lanthanide metal ion, incorporated into tetraphenylporphyrin or octaethylporphyrin, is added to a plasticized poly(vinyl chloride) membrane. The selectivity coefficients of the resulting membrane electrodes differ from the traditional Hofmeister series, with a preference towards the salicylate anion, while discriminating thiocyanate and iodide. Through separate incorporation of lipophilic ionic additives, the lutetium(III) porphyrin-based electrodes were determined to function via a neutral carrier mechanism. As a result, the addition of cationic (quaternary ammonium) salts to the membrane enhances the response characteristics of the electrodes. An initial study to determine the feasibility of utilizing these electrodes in clinical determinations of salicylate is also demonstrated. Membrane composition and sample pH are varied to optimize salicylate response in the clinical range of salicylate concentrations.