I3-sensitive sensor; neutral red; ionic acetate; electrode function; density; peroxo compounds; peroxide number; potentiometric titration.

I3-sensitive sensor was developed, where the ionic acetate of the neutral red triiodide was used as the electrodoactive substance. The main electroanalytical characteristics of the sensor have been studied. It is established that the operating interval of the pH of the chain is 2–12. The interval of linearity of the electrode function is 9×10–5 – 1×10–1 mol/l, the slope is 51–59 mV/pC. The selectivity of the triiodide sensor by the “individual-solutions” method has been studied.