I incubated some samples containing oil-contaminated sediments. from the sediment prior to spiking it with oil, I took a clean sample and dried it in the oven to know the percentage of dry content I have in my sample. My question is, do I use this dry weight percentage after getting the TPH results or the samples should be dried separately during extraction and dry weight percentage should be calculated for each sample individually?
I hope my question is clear. Thanks for your help in advance
Measuring dry weight of a sediment requires heating at about 110 degrees C until there is no change in weight. The mineralogy of the sample is critical because higher temperatures such as over 250 degrees C will result in decomposition of minerals such as montmorillonite and other hydrated minerals. If you have organic matter present, it will tend to dry out and upset your results. In that case, drying should be carried out at about 20 degrees C to avoid errors due to decomposition or burning of the organic matter. Oil contaminated samples are a problem since heating will tend to cause loss of the more volatile components in the sample. You must know the variability in dry and wet weight of multiple uncontaminated sediment samples if you are comparing the results with contaminated samples. You should probably weigh the oil aliquot that you are adding to the soil in your spiking so that you can check for losses of volatile chemicals in the subsequent drying process. I hope this helps.
Stuart.
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