Organic matter extractable molecules

According to their acidity, humic substances are hydrophobic and are split into two groups humic and fulvic acids. Humic acids are stable molecules originating from the ageing of organic matter. They are responsible for water coloration and represent 40-60% of natural organic matter in rivers and lakes. Fulvic acids are smaller than the humic acids and are generally less aromatic than humic acids extracted from the same pool of DOM. 

Steroids are hydrophobic molecules and sparingly soluble with only one hydroxyl functional group. Normally steroids are found concentrated in the sediment phase via partitioning onto organic matter on sediments (25). Their concentration in the foam and humic-acid fraction is indicative of the hydrophobic nature of these fractions. The increasing compositional complexity from stream, to foam, to foam-extract samples is also consistent with other characterization trends of increasing compositional complexity and hydrophobicity. 

Very recently , we have carried out an intercomperison study of hquid-hquid extraction (LLE) and sorption on polyurethane foam (PUF) and Amberlite XAD-2 for the analysis of aliphatic, aromatic and chlorinated hydrocarbons dissolved in seawater. The application of these methods, sampling in parallel the same body of water, has shown significant differences in the recovery of higher molecular weight components in the complex mixtures of both aliphatic and aromatic hydrocarbons. These are attributed to selective associations of these hydrophobic species with macromolecular organic matter such as fulvic and humic acids and to the effects of the dissolved organic molecules on adsorbent properties. 

The extractible fraction itself contains hundreds of compounds, and only a limited number can be routinely analysed. Among these molecules, the family of polycyclic aromatic hydrocarbons has been by far the most extensively studied, in terms of mechanism and properties. PAH are indeed quite easily produced in laboratory flames and can be routinely analysed, at least for molecdles with masses lower than 300 a.m.u. During the workshop, several papers have discussed in detail the analysis of polycyclic organic matter. However, as a brief introduction, it is useful to define the different compounds considered. 

The principal task is to decipher the complex mixture of molecules that comprise sedimentary organic matter. In general, this aim focuses on the extractable components, but a variety of procedures including pyrolysis and chemical degradation permit assessment of compounds released from the insoluble kerogen (75). 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

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