Determination of Low Molecular Weight Dicarboxylic and Ketocarboxylic Acids in Seawater Samples
Résumé
We report a new method developed for the isolation and determination of low molecular weight dicarboxylic acids and related polar compounds (C 2-C 9) from seawater samples. The seawater sample was first acidified and then passed through an activated charcoal column to adsorb the dicarboxylic acids. They are then desorbed with NH 4 OH/methanol/water mixture and derivatized with BF 3 /1-butanol to dibutyl esters, which are determined using a capillary GC/FID. We tested different pH (0.5, 1, 1.5) and different amounts of charcoal (100, 200, 300, 500 mg) to maximize the recovery of dicarboxylic acids. Using 300 mg of activated charcoal for 100 mL of sodium chloride solution acidified at pH 1, the recoveries for C 2 , C 3 , C 4 , C 5 , C 6 , C 7 , C 8 , and C 9 were 61, 49, 96, 84, 77, 67, 57, and 53%, respectively. We applied this method to real seawater samples collected from the northwestern Mediterranean Sea. Here, we report, for the first time, concentrations of a homologous series of C 2-C 9 dicar-boxylic acids as well as ketocarboxylic acids including glyoxylic and 4-oxobutanoic acids in surface water and deep seawater samples, with glyoxylic acid being the dominant species (8-40 µg L-1). This method allows the detection of dicarbonyls such as glyoxal in the samples although its quantification is not possible. Low molecular weight (LMW) dicarboxylic acids and related polar compounds (DCAs) (C 2-C 9) are ubiquitous water-soluble organic compounds that have been detected in a variety of environmental samples including atmospheric aerosols, 1,2 rainwa-ters, 3 snowpacks, 4 ice cores, 5 meteorites, 6 marine sediments, 7,8 hypersaline brines, 9 and freshwaters. 10-12 In the atmosphere, DCAs originate from incomplete combustion of fossil fuels, 13 biomass burning, 14 direct biogenic emission, 15 and ozonolysis and photo-oxidation of organic compounds. 16,17 Because of their hygroscopic properties, DCAs can act as cloud condensation nuclei and have an impact on the radiative forcing at the Earth's surface. 18 DCAs also participate in many biological processes. They are important intermediates in the tricarboxylic acid and glyoxylate cycles and the catabolism and anabolism of amino acids. 19 In seawater, DCAs may be produced by phytoplankton pho-torespiration, 20 photochemical degradation of dissolved organic matter (DOM), 21,22 and microbial degradation of long-chain lipids. 23 Other possible sources of DCAs in seawater include diffusion from surface sediments (especially for oxalic acid), 7 inputs of terri-genous material from rivers, 22 and wet and dry depositions. 16 Therefore, DCAs could represent a non-negligible fraction of LMW DOM and have a potential role in the organic carbon cycle in the marine environment. However, only a few studies have reported concentrations of DCAs or related compounds in seawater. In the Pacific Ocean and coastal waters off California and Peru, one dicarboxylic acid, i.e., oxalic acid, and two ketocarboxylic acids (glyoxylic and pyruvic) were detected by reversed-phase and size exclusion HPLC using derivatization with o-phenelene diamine followed by an acetonitrile extraction. 19,20 In the Sargasso Sea and coastal waters off Florida, ketocarboxylic acids (glyoxylic and pyruvic) and dicarbonyls (methylglyoxal and glyoxal) were * Corresponding author. Fax: 33 04 91 82 96 41. Ojanen, C.; Pakkanen, T.; Hillamo, R.; Aurela, M.; Merilainen, J.
Domaines
Océan, Atmosphère
Origine : Fichiers produits par l'(les) auteur(s)
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