Comprehensive Molecular Characterization Of Organic Contaminants In Freshwater Sediments By Gas Chromatography/Mass Spectrometry And Liquid Chromatography/Time-Of-Flight Mass Spectrometry

A complex scheme for a broad-spectrum molecular characterization of organic contaminants in polluted freshwater sediments has been developed. The extracts were prepared by an exhaustive accelerated solvent extraction procedure, covering both hydrophobic and polar organic contaminants. Before analysis using mass spectrometric techniques, including gas chromatography/mass spectrometry (GUMS) and liquid chromatography/quadrupole time-of-flight mass spectrometry (LC-QToF), the extracts were fractionated into three distinct fractions on a silica gel column, involving sequential elution with hexane, dichloromethane and methanol as elating solvents. The first two fractions, containing nonpolar and medium polar contaminants, respectively, were characterized by electron impact GUMS, while LC-QToF was applied for the analysis of the polar contaminants contained in dichloromethane and methanol fractions. The developed analytical scheme was applied for the molecular characterization of contaminants in polluted freshwater sediments, collected in the area of the city of Zagreb, Croatia. The analyses showed a significant presence of classical non-polar contaminants such as petroleum hydrocarbons and polycyclic aromatic hydrocarbons however they also revealed the importance of some polar compound classes, which possess a hydrophobic moiety (surfactants and their metabolites, sterols, fatty acids). As expected, the results showed that polar contaminants lacking a hydrophobic moiety were much less abundant, but in some samples significant levels of highly polar pharmaceuticals were detected. The application of LC-QToF allowed a successful identification of several non-target organic contaminants of pharmaceutical origin using accurate mass determination, thorough data-base search and subsequent confirmation of tentatively identified compounds by comparison with corresponding reference compounds. The combination of GC/MS and LC-QToF techniques showed clear advantages over the single-technique approach in providing a much broader analytical window for identification of specific organic contaminants, which might be essential for a better ecotoxicological assessment of polluted freshwater sediments.