Ion-selective electrode for dodecyldimethylamine oxide: A "twice-Nernstian" slope for the determination of a neural component

An electrode originally sensitive to dodecyltrimethylammonium (DTA(+)) was proven to be sensitive to dodecyldimethylamine oxide (DDAO), a surfactant w ith acido-basic properties. The response of the electrode was tested from p H 2 to 9.3, Its slope is Nernstian when the surfactant is entirely protonat ed. At a pH where the molecule is mainly under the neutral form, the electr ode responds with a "twice-Nernstian" slope around 120 mV/decade. The valid ity of this electrode for measurements was checked by confronting the evolu tion of the critical micelle concentration of DDAO vs pH with data already published and by determining the complexation constant of DDAO and beta-cyc lodextrin. A possible explanation of the "twice-Nernstian" slope, using a d imer of DDAO is proposed.