Resumo:
Te performance of gas chromatography coupled to high-resolution time-of-fight mass spectrometry (GC-HRTofMS) for
characterizing geochemical biomarkers from sediment samples was evaluated. Two approaches to obtain the geochemical
biomarkers were tested: (1) extraction with organic solvent and subsequent derivatization and (2) in-situ derivatization thermal
desorption. Results demonstrated that both approaches can be conveniently applied for simultaneous characterization of
many geochemical biomarkers (alkanes, alkanols, sterols, and fatty acids), avoiding conventional time-consuming purifcation
procedures. GC-HRTofMS reduces both sample preparation time and the number of chromatographic runs compared to traditional
methodologies used in organic geochemistry. Particularly, the approach based on in-situ derivatization thermal desorption
represents a very simple method that can be performed in-line employing few milligrams of sediment, eliminating the need for any
sample preparation and solvent use. Te high resolving power (m/Δm50% 25,000) and high mass accuracy (error ≤ 1 ppm) ofered
by the “zig-zag” time-of-fight analyzer were indispensable to resolve the complexity of the total ion chromatograms, representing
a high-throughput tool. Extracted ion chromatograms using exact m/z were useful to eliminate many isobaric interferences
and to increase signifcantly the signal to noise ratio. Characteristic fragment ions allowed the identifcation of homologous
series, such as alkanes, alkanols, fatty acids, and sterols. Polycyclic aromatic hydrocarbons were also identifed in the samples
by their molecular ions. Te characterization of geochemical biomarkers along a sedimentary core collected in the area of Valo
Grande Channel (Canan´eia-Iguape Estuarine-Lagunar System (S˜ao Paulo, Brazil)) provided evidences of environmental changes.
Sediments deposited before opening of channel showed dominance of biomarkers from mangrove vegetation, whereas sediments
of the pos-opening period showed an increase of biomarkers from aquatic macrophyte (an invasive vegetation).
