Evaluation of extraction schemes for organic matter in anoxic estuarine sediments

A persistent criticism of studies of organic matter in sediments and soils has been that the extracted products used in these investigations may not resemble the original material, particularly if harsh extractants such as NaOH, Na₄P₂O₇ or HCl are employed. To minimize chemical changes, a mild separation procedure has been developed for obtaining soluble organic matter from anoxic estuarine sediments. The resulting complex mixture of organic compounds can be analyzed by reversed-phase liquid and size-exclusion chromatographic methods, which monitor the relative molecular polarity and size, respectively. The effects of the strong reagents NaOH, Na₄P₂O₇ and HCl, as well as exposure to the atmosphere and bacterial activity on this anoxic sedimentary extract has been investigated. In each instance, significant degradation of anoxic organic matter occurs, producing molecules of increased polarity and reduced molecular weight. These data indicate that extreme care is necessary to avoid artifacts in preparation and handling of samples.