Gas chromatography coupled to high resolution time-of-flight mass spectrometry as a high-throughput tool for characterizing geochemical biomarkers in sediments

Abstract

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).