Anal. Chem. 1994,66, 2921-2925
H202Determination by the Is- Method and by KMn04 Titration Norman V. Kiassen,' David Marchington, and Heather C. E. McGowant Institute for National Measurement Standards, Ionizing Radiation Standards, National Research Council Canada, Ottawa K1A OR6 Canada The analysis of aqueous H202 at concentrations as low as 1 pM is conveniently done by the 13- method, which is based on the spectrophotometric determination of 13- formed when Hz02 is added to a concentrated solution of I At 351 nm, emx(I;) was measured to be 26 450 M-l cm-l. By contrast, an apparent value of 25 800 M-' cm-l was determined from a calibration of the 13- method against titration by permanganate. The difference could only be partially accounted for by the equilibrium between 13; 12, and I-. A further correction of -1% was required and was traced to a side reaction between HzOz and the buffer normally used in the 13- method. A simple spectrophotometric procedure was developed which improves the sensitivity of the permanganate titration to 0.3 pM HzO2. Measurements of H202 using the oxidation of ferrous ions (Fricke solution) and permanganate titration differed by less than 1%.
-.
Schumb, Satterfield, and Wentworthl considered the permanganate titration to be one of the most exact and reliable analytical procedures for HzO2. The reaction follows the stoichiometry 2Mn0;
+ 5H20z+ 6H'
-
+
2Mn2+ 8 H z 0
+ 50,
which was confirmed to -1 part in 5000 by Huckaba and Keyes2 The sensitivity of the permanganate end point, when observedvisually, is 3 pM HzO2.l We now present a simple way to improve the sensitivity to 0.3 pM H202 by titrating to the visible end point and determining the excess KMn04 by optical absorption. However, this new method does not remedy the problem that the analysis of
