Ion-Selective Electrode for Dodecyldimethylamine Oxide: A “Twice-Nernstian” Slope for the Determination of a Neutral Component

An electrode originally sensitive to dodecyltrimethylammonium (DTA⁺) was proven to be sensitive to dodecyldimethylamine oxide (DDAO), a surfactant with acidobasic properties. The response of the electrode was tested from pH 2 to 9.3. Its slope is Nernstian when the surfactant is entirely protonated. At a pH where the molecule is mainly under the neutral form, the electrode responds with a “twice-Nernstian” slope around 120 mV/decade. The validity of this electrode for measurements was checked by confronting the evolution of the critical micelle concentration of DDAO vs pH with data already published and by determining the complexation constant of DDAO and β-cyclodextrin. A possible explanation of the “twice-Nernstian” slope, using a dimer of DDAO is proposed.