Natural organic matter: study by two-dimensional liquid chromatography

• Autor(a) principal: Barros, Ana Carolina Cardoso Alves de
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/7814
• topic: Química analítica; Matéria orgânica; Cromatografia líquida

For the purpose of resolving the chemical heterogeneity of natural organic matter (NOM), comprehensive two-dimensional liquid chromatography (LC x LC) was employed for the first time to map the hydrophobicity and polarity vs. molecular weight (MW) distribution of the following complex organic mixtures: Suwannee River (SR-FA) and Pony Lake (PL-FA) Fulvic Acids, both obtained from the International Humic Substances Society, and water-soluble organic matter (WSOM) from atmospheric aerosols. Two methods have been developed using either a conventional reversed-phase silica column (RP-C18) or a mixed-mode hydrophilic interaction column (mixed-mode HILIC) in the first dimension, and a size-exclusion column (SEC) in the second dimension. The RP-C18 x SEC and mixed-mode HILIC x SEC fractions were screened on-line by UV at 254 nm, molecular fluorescence at excitation/emission wavelengths (Exc/Em) of 240/450 nm, and by evaporative light scattering. The MW distributions of these NOM samples were further characterized by number average molecular weight (Mn), weight average molecular weight (MW), and polydispersity (Mn/Mw). Findings suggest that the combination of two independent separation mechanisms is promising in extend the range of NOM separation. The complete range of Mw values obtained in this study varied within 745-2122 Da, 637-1950 Da, and 157-891 Da for the SR-FA, PL-FA and WSOM, respectively. The obtained results were associated to the different origin and formation pathways of the three NOM samples, which strongly influence their chemical composition and MW distribution.