Potentiometric behavior of metalloporphyrin-based ion-selective electrodes: Use of silicone rubber matrix for serum chloride analysis Original Research Article

For the proper design of a miniaturized all-solid-state chloride-selective electrode for serum analysis with metalloporphyrin-based ionophores, the potentiometric behavior of four different metalloporphyrins, i.e., manganese(III) tetraphenylporphyrin chloride [Mn(TPP)Cl], manganese(III) octaethylporphyrin chloride [Mn(OEP)Cl], indium(III) tetraphenylporphyrin chloride [In(TPP)Cl] and indium(III) octaethylporphyrin chloride [In(OEP)Cl], doped in a one-component room temperature vulcanizing-type silicone rubber (SR) matrix were examined. Particular attention was paid to find a membrane formulation with minimal effect of salicylate because this interference is often the cause of a large positive error in serum chloride analysis. In general, the use of 10–20 wt% of plasticizer (e.g., o-nitrophenyl octyl ether (NPOE) and dibutyl sebacate (DBS)) was necessary for the ion carriers in SR to induce proper potentiometric response to chloride. On the other hand, In(TPP)Cl doped in SR matrix did not show any electrochemical activity regardless of the type of plasticizer employed. Mn(OEP)Cl or In(OEP)Cl doped in SR matrix with NPOE plasticizer exhibited super-Nernstian response (70.8 and 84.0 mV/pCl−, respectively), while those with DBS plasticizer show sub-Nernstian behavior. Of the two octaethyl porphyrins, the In(OEP)Cl-based membrane exhibited higher slope, 53.7 mV/decade, to chloride with reduced salicylate interference (log KPOTCl−,sal−=1.1 with DBS). All-solid-state electrodes modified with In(OEP)Cl/SR/DBS membranes have been prepared and their utility for serum chloride measurement have been demonstrated.