POTENTIOMETRIC BEHAVIOR OF METALLOPORPHYRIN-BASED ION-SELECTIVE ELECTRODES - USE OF SILICONE-RUBBER MATRIX FOR SERUM CHLORIDE ANALYSIS

For the proper design of a miniaturized all-solid-state chloride-selec tive electrode for serum analysis with metalloporphyrin-based ionophor es, the potentiometric behavior of four different metalloporphyrins, i .e., manganese(III) tetraphenylporphyrin chloride [Mn(TPP)Cl], mangane se(III) octaethylporphyrin chloride [Mn(OEP)Cl], indium(III) tetraphen ylporphyrin chloride [In(TPP)Cl] and indium(III) octaethylporphyrin ch loride [In(OEP)Cl], doped in a one-component room temperature vulcaniz ing-type silicone rubber (SR) matrix were examined. Particular attenti on was paid to find a membrane formulation with minimal effect of sali cylate because this interference is often the cause of a large positiv e error in serum chloride analysis. In general, the use of 10-20 wt% o f plasticizer (e.g., o-nitrophenyl octyl ether (NPOE) and dibutyl seba cate (DBS)) was necessary for the ion carriers in SR to induce proper potentiometric response to chloride. On the other hand, In(TPP)Cl dope d 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 sh ow 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 K-Cl-, sal-(POT) = 1.1 with DBS). All-solid-state electrodes modified with In(OEP)Cl/SR/DBS membr anes have been prepared and their utility for serum chloride measureme nt have been demonstrated. (C) 1998 Elsevier Science B.V. All rights r eserved.