Organic compounds formed by chemical degradation of lake aquatic humic matter

Abstract

Composition of dissolved organic matter (DOM) from Lake Savojärvi was studied by the CuO-oxidation method. The mixtures of the degradation products were fractionated by gas chromatography into individual components and identified by mass spectrometry. Oxidation of organic macromolecules with CuO takes place by various mechanisms, making it somewhat difficult to build a model for the original composition/structure of the DOM. However, with the aid of data treatment based on the degradation products, it is possible to describe some detailed features of humic structure. The quantified yields of oxidation products varied from 54 to 362 mg per 1 g of the humic material by dry weight, depending on the source of the sample and the isolation method applied. Almost all degradation products resulting from the CuO-oxidation method were in the form of acid derivatives. As a rule, the major fraction of the oxidation products consisted of different kinds of aliphatic compounds (60–71%), especially those of low molecular weight. The degree of linking of the structural units and the reason for variable amounts of oxidation products were compared for humic samples from two different sources. Differences were found mainly between individual humic and fulvic acid fractions, whereas average values calculated for combined humic and fulvic acid fractions, taken to represent the original humic solutes in the water samples, indicated only minor differences.