Determination of diclofenac in pharmaceuticals using a metalloporphyrin-based selective electrode

摘要

The construction and the potentiometric response characteristics of a new diclofenac-selective electrode based on rhodium(III)tetraphenylporphyrin (Rh(III)TPP-Cl) as an ionophore are presented. The ionophore was incorporated into a PVC matrix. The effect of lipophilic cationic and anionic additives on the potentiometric response was investigated. The best results were obtained for the membrane having the cationic additive trioctylmethylammonium chloride (TOMACl) added. The corresponding sensor exhibited a near-Nernstian response to diclofenac in the concentration range 5×10~(-6)-1×10~(-2) M with a slope of -59.4mV per concentration decade in a buffer solution of pH 7.1. The selectivity of the sensor relative to a lot of organic and inorganic anions is also reported. This electrode was applied for the direct determination of diclofenac in pharmaceutical formulations and the results were compared with those provided by the HPLC reference method.