Characterization of organic matter from natural waters using tetramethylammonium hydroxide thermochemolysis GC-MS

The tetramethylammonium hydroxide (TMAH) thermochemolysis method was recently introduced for the qualitative characterization of organic matter from natural waters (NOM). Such characterizations were usually of a qualitative nature, and any semiquantitative assessments of individual compounds were often achieved by measuring relative areas and assuming unity as a response factor. In this paper we evaluate the quantitative measurement of many identified products characteristic of lignin and NOM using an internal standard approach. The relative standard deviation for most quantified compounds was between 1 and 10%. Four NOM samples, isolated by low-temperature, low-pressure evaporation and freeze-drying, were collected from temperate as well as tropical climates. Large variations were found between samples with respect to the distribution of compounds such as fatty acids, lignin-derived compounds, carbohydrate-derived compounds, and protein-derived compounds. We quantified most lignin-derived and aromatic TMAH products as well as fatty acids (as their methyl esters, FAME) that were found in this set of NOM samples. The contribution of lignin-derived compounds to the total quantified TMAH product distribution in these four samples varied between 21 and 35%. The contribution of FAMEs ranged from 32 to 51% whereas the contribution from non-lignin aromatic compounds was 24-32%. TMAH thermochemolysis potentially provides significant information about NOM sources, compared with other degradative techniques, since both lignin-derived compounds and lipids can be quantitatively and simultaneously investigated.