Caracterisation de la matiere organique dissoute de l'estuaire du Saint-Laurent par un systeme HPLC-FTIR

Because of its complex and altered nature, dissolved organic matter (DOM) in aquatic environments is very difficult to characterize. Consequently, a large portion of its composition remains unknown. However, the coupling of analytical techniques can provide structural information about this complex mixture. In this study, a solvent-elimination interface was used to couple high-performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy (FTIR). Size-exclusion chromatography (SEC) was used to apply a molecular size-based separation. This system enabled the characterization of ultrafiltered DOM (UDOM) and fulvic acid (FA) samples from the St. Lawrence Estuary and its tributaries and the quantification of functional groups present in the different size fractions. Compositional differences were observed in function of molecular size, the geographic origin of samples and the type of sample (fulvic acids vs. UDOM). These compositional differences in regard to molecular size support a previously proposed model that links the reactivity of DOM molecules to their size. For example, large UDOM molecules were enriched in amides, carbohydrates and alkanes, while small terrigenous molecules were enriched in carboxylates and hydroxyl groups, and small marine molecules were enriched in sulfates and OH groups. The composition of UDOM was found to vary appreciably through a range of molecular sizes, but the composition of FA were quite stagnant, with strong signals of carboxylates and OH groups. This study showcases the potential of the solvent-elimination HPLC-FTIR interface as a characterization tool for DOM because of the quality of the structural information obtained. This system thus has some advantages over other available methods, and can provide complementary information to even the most sophisticated mass spectrometry techniques.;This thesis also includes results and observations obtained during the development and optimization of the LC-Transform, the solvent-elimination HPLC-FTIR interface, as well as the Optics Module 3000.