H2O2 DETERMINATION BY THE I-3(-) METHOD AND BY KMNO4 TITRATION

The analysis of aqueous H2O2 at concentrations as low as 1 mu M is conveniently done by the I-3(-) method, which is based on the spectrophotometric determination of I-3(-) formed when H2O2 is added to a concentrated solution of I-. At 351 nm, epsilon(max) (I-3(-)) was measured to be 26 450 M(-1) cm(-1). By contrast, an apparent value of 25 800 M(-1) cm(-1) was determined from a calibration of the I-3(-) method against titration by permanganate. The difference could only be partially accounted for by the equilibrium between I-3(-), I-2, and I-. A further correction of similar to 1% was required and was traced to a side reaction between H2O2 and the buffer normally used in the I-3(-) method. A simple spectrophotometric procedure was developed which improves the sensitivity of the permanganate titration to 0.3 mu M H2O2. Measurements of H2O2 using the oxidation of ferrous ions (Fricke solution) and permanganate titration differed by less than 1%.