Behavior of a polypyrrole solid contact pH-selective electrode based on tertiary amine ionophores containing different alkyl chain lengths between nitrogen and a phenyl group.

We compared the slopes of the EMF responses and the response range of a solid contact electrode based on a tribenzylamine ionophore with those based on a tris(2-phenylethyl)amine ionophore and a tris(3-phenylpropyl)amine ionophore. Their slopes of the EMF responses showed, respectively, 57.7, 58.1, 59.0 mV pH(-1) (at 20 +/- 0.2 degrees C). Also, the linear pH response dynamic ranges were 2.74-10.63 for tribenzylamine-based SCEs, pH 4.47-12.59 for tris(2-phenylethyl)amine, and pH 4.60-13.24 for tris(3-phenylpropyl)amine. When the slopes of the EMF responses and the response range were considered, as the length of the replaced alkyl chain increased between the nitrogen atom and the phenyl group in the ionophore, though the dynamic range and the slopes of the EMF responses of these electrodes did not show any particularly different results, their response ranges moved toward the alkali range (shifted to pH 14). When it was directly applied to cow's milk (in pH range of 6.0-8.5), we could obtain the same satisfying results. This electrode continuously contacted a Tris 7.50 buffered solution as well as cow's milk for one month without any loss of performance. Also, especially, these electrodes showed very good results, such as stabilization of the base potential as well as the best reproducibility and response time (< 10 s).