To map the ischemic regions of a heart, cardiologists must ligate a blood vessel and measure changes in the various ion concentrations over time. The plunge wire electrodes that are used are subject to failure from a multitude of causes, one of which may involve the degradation of the pH-selective ionophore, tri-n-dodecylamine (TDDA). In this work, the stabilities of four commercial products were studied by TGA in 100% N-2, air, and 100% O-2. No significant difference in thermal stabilities or activation energies were noted. When mixtures of TDDA and four antioxidants were studied, no improvement in the rate of weight loss was noted. When accelerated aging tests were performed and these products were incorporated into membranes, the loss in pH sensitivity was apparent after only 10 min at 200 degrees C in 100% O-2. From TGA, NMR, and IR analyses, a cleavage mechanism is suggested that involves the formation of dodecane and a secondary amide, didodecylamide.