Method and chemical sensor for determining concentrations of hydrogen peroxide and its precursor in a liquid

A method for measuring H.sub.2 O.sub.2 concentration in a solution comprising the following steps:

• a) immersing a counter electrode, a reference electrode and a chemical sensor as a working electrode into a solution under reaction conditions;
• b) obtaining a steady electric current from the working electrode by amperometry, wherein a fixed potential between the working electrode and the reference electrode is maintained, and said fixed potential ranges from 0V to -200 mV when the reference electrode is a 3 M KCl Ag/AgCl electrode;
• and
• c) comparing the steady electric current from b) with steady electric currents obtained from solutions having known H.sub.2 O.sub.2 concentrations under substantially the same operating conditions and the same fixed potential used in steps a) and b);
• wherein the operating conditions comprised maintaining the solution in a homogenous phase by stirring, and maintaining a substantially constant pH by adding a pH-buffer, and selectively adding an electrolyte to the measured solution, wherein the substantially constant pH is between 3 to 7;
• said chemical sensor comprising a transducer which is able to conduct an electric current and a mixed-valence compound deposited on a surface of the transducer, wherein said mixed-valence compound has a formula as follows:
• M.sub.y.sup.z+ [Fe(II)(CN).sub.6 ]
• wherein M is Co, Ni, Cr. Sc, V, Cu, Mn, Ag, Eu, Cd, Zn, Ru, or Rh;
• z is the valence of M;
• and y=4/z.