Construction and analytical applications of liquid membrane electrode for trinitrobenzenesulfonic acid (TNBS)

A new liquid membrane electrode which responds to trinitrobenzenesulfonate (TNBS^?) ion is described. The electrode exhibits very good experimental characteristics: (i) The working pH range is 2.0–12.5; (ii) its response is consistent with the Nernst equation in the range 1.10^?1–5.10^?5m; (iii) its response time is 5 s; and (iv) its selectivity for TNBS^? against 14 tested ions is very high. Ions such as $\text{ClO}{}_4{}^{\mathrm{?}}$, $\text{IO}{}_4{}^{\mathrm{?}}$, I^?, and biphthalates interfere with potentiometric selectivity coefficients in the range 1.0 × 10^?2–9.0 × 10^?2. The electrode is suitable for direct potentiometry, potentiometric titrations, and kinetic potentiometric methods. Instructions for the application of the electrode for the potentiometric assay of aminoacids are given. The application of the electrode in the potentiometric precipitation titration of methylene blue with TNBS, and its use in the kinetic potentiometric determination of aminoacids is also described. The electrode has very good slope stability (60 mV/decade change of activity) for a period ofat least 2 months.