Analytical Interferences Caused by Residual Hydrogen Peroxide
Hydrogen peroxide has three properties which may cause it to interfere with conventional analytical procedures:
H2O2 is an oxidizing agent.
H2O2 + 2H+ + 2e- → 2H2O (1.776 mV)
This may affect procedures which: a) rely on redox reagent (e.g., iodine titrations); b) involve an oxidant-sensitive indicator or reactant (e.g., methylene blue); or c) involve biological organisms or products which are affected by oxidants (e.g., bioassays).
H2O2 may also be a reducing agent.
H2O2 + 2OH- → O2 + H2O + 2e- (-0.146 mV)
H2O2 will reduce some oxidants such as hexavalent chromium (under acid conditions) and hypochlorite (under alkaline conditions).
H2O2 liberates oxygen.
H2O2 → O2 + H2O
Two lbs H2O2 (as 100%) will liberate one lb of oxygen. The rate of evolution will vary from minutes to years depending on a number of factors. In typical domestic wastewaters the half-life of 10 mg/L H2O2 is about an hour, while that of 100 mg/L may be 1-2 days. This has obvious ramifications for determining, e.g., Biochemical Oxygen Demand (BOD).
Summary of Known Interferences with Analytical Methods
The table below lists those specific analyses in which H2O2 is known to interfere.
| Analysis | Procedure | Affect |
|---|
| Biochemical Oxygen Demand | Oxygen Uptake | Reduces Value |
| Chemical Oxygen Demand | Dichromate Digestion | Increases Value |
| Sulfide | Methylene Blue | Reduces Value |
| Sulfide | Iodine Titration | Reduces Value |
| Sulfide | Iodine Titration | Reduces Value |
| Thiosulfate | Iodine Titration | Reduces Value |
Removing Interferences Due to Hydrogen Peroxide
The best remedy is to remove residual H2O2 prior to the analysis either by selective separation or H2O2 destruction (either through decomposition or neutralization). Four commonly used sample pretreatment procedures follow. You should choose the method most compatible with your analytical method. A simple technique for confirming the removal utilizes the EM QuantTM Peroxide Test Strips (from EM Science, Gibbstown, New Jersey, 08027).
Catalase enzyme.
This is the more versatile procedure because of its high selectivity to H2O2. The mechanism of removal is catalytic decomposition of the H2O2 to oxygen and water. Two forms (derivations) of the enzyme are available: 1) bovine liver; and 2) Aspergillis niger. The latter has the advantage of retaining activity over a wider range of pH and temperature conditions. The amount of enzyme added depends on its activity and the time permitted before analysis - you should consult the label for this information. In using this procedure it is important to quantify the impact of the enzyme on your analysis. This is best done by adding an identical amount of enzyme to a sample of deionized water, performing your analysis on this sample, and subtracting the value from the pretreated sample.
Elevated pH and temperature.
The rate of H2O2 decomposition (to oxygen and water) increases several fold as pH increases and temperature rises. For treated samples of industrial waste containing several hundred mg/L H2O2, it may be possible to raise the pH to 10-11 and the temperature to 40-50 deg-C and allow the sample to sit overnight. This process may be further accelerated by the addition of iron (III) compounds.
Chemical neutralization.
Bisulfite (or sulfite) reacts quickly to remove residual H2O2, as it does with other oxidants. Again, however, over-addition may impact the analysis, and quantifying the effect is not as straightforward as with catalase enzyme.
Decomposition by Activated Carbon.
H2O2 is decomposed heterogenously by activated carbons; however, the rate is greatly affected by the type of carbon. Carbons which perform best are either catalytically-active (e.g., Calgon's CentaurTM Carbon) or impregnated with catalytically-active metals such as copper, chrome, or silver. The rate of H2O2 removal by any carbon may be greatly increased by raising the pH and/or temperature.