A solid-state redox buffer as interface of solid-contact ISEs

Graphite with a surface-confined redox buffer system was used as solid contact in solid-contact ion-selective electrodes (SC-ISE). Potentiostatically preconditioning of the redox buffer ensures that the ratio of oxidized and reduced groups is unity, i.e., a maximum buffer capacity. These SC-ISEs exhibited a very high reproducibility and stability of potentials. Graphite modification was achieved by generating carboxylic surface groups via oxidation with nitrosulfuric acid and subsequent modification of the acidic groups with n-(2,5-dimethoxyphenyl)ethyl-1-amine (DMPEA). Composite electrodes of modified graphite and polymethylmetharcrylate (PMMA) as binder were used as solid-contact of polymer membrane K⁺-and F^?-sensitive SC-ISEs. The solid-state redox buffer decreased potential variation from several hundred mV to just a few mV.