My samples are very high in organic matter, and even small amounts of H2O2 cause the samples to foam up 4-5 times the beaker volume, spilling onto the lab bench. Is there anything that can be done to manage this, other than adding smaller volumes of H2O2 or digesting smaller soil samples?
This same problem occurs with plant samples and the solution there is smaller samples and cooling (standing the digestion containers in water) until the first vigorous reaction has subsided. Strange as it sounds, I have sometimes had success with more peroxide than less.
Place about 10 g air dry soil containing no particles larger than 2 mm in a polythene bottle. Add 50 ml of NaOAc solution (pH 5-6), warm on water bath. Then centrifuge and decant the supernatant. After removal of excess salts and CaCO3, follow the treatment of H2O2 for removal of organic matter. Add 5 ml of H2O2 in a sample previously treated to remove soluble salts and carbonates. Add H2O2 in increments of 5 to 10 ml or less, stir the suspension, and allow time for any strong effervescence or frothing to subside. Place it on a water bath to warm. Remove the centrifuge bottle from the water bath and allow it to cool. The reaction of soil with H2O2 is essentially complete when the soil sample loses its dark colour or when conspicuous effervescence ceases. Some effervescence will always be present due to the decomposition of the H2O2. Centrifuge the bottles and decant the supernatant. The sample is now ready for the next step.
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