title: High-throughput characterization of sediment organic matter by pyrolysis-gas chromatography/mass spectrometry and multivariate curve resolution: A promising analytical tool in (paleo)limnology.
abstract: Molecular-level chemical information about organic matter (OM) in sediments helps to establish the sources of OM and the prevalent degradation/diagenetic processes, both essential for understanding the cycling of carbon (C) and of the elements associated with OM (toxic trace metals and nutrients) in lake ecosystems. Ideally, analytical methods for characterizing OM should allow high sample throughput, consume small amounts of sample and yield relevant chemical information, which are essential for multidisciplinary, high-temporal resolution and/or large spatial scale investigations. We have developed a high-throughput analytical method based on pyrolysis-gas chromatography/mass spectrometry and automated data processing to characterize sedimentary OM in sediments. Our method consumes 200 μg of freeze-dried and ground sediment sample. Pyrolysis was performed at 450°C, which was found to avoid degradation of specific biomarkers (e.g., lignin compounds, fresh carbohydrates/cellulose) compared to 650°C, which is in the range of temperatures commonly applied for environmental samples. The optimization was conducted using the top ten sediment samples of an annually resolved sediment record (containing 16-18% and 1.3-1.9% of total carbon and nitrogen, respectively). Several hundred pyrolytic compound peaks were detected of which over 200 were identified, which represent different classes of organic compounds (i.e., n-alkanes, n-alkenes, 2-ketones, carboxylic acids, carbohydrates, proteins, other N compounds, (methoxy)phenols, (poly)aromatics, chlorophyll and steroids/hopanoids). Technical reproducibility measured as relative standard deviation of the identified peaks in triplicate analyses was 5.5±4.3%, with 90% of the RSD values within 10% and 98% within 15%. Finally, a multivariate calibration model was calculated between the pyrolytic degradation compounds and the sediment depth (i.e., sediment age), which is a function of degradation processes and changes in OM source type. This allowed validation of the Py-GC/MS dataset against fundamental processes involved in OM cycling in aquatic ecosystems.
authors.affiliation: Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden. Electronic address: julietolu@hotmail.com.
authors.forename: Julie
authors.initials: J
authors.lastname: Tolu
authors.affiliation: Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology, SE-901 83 Umeå, Sweden.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Gerber
authors.affiliation: Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Boily
authors.affiliation: Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Richard
authors.initials: R
authors.lastname: Bindler
mesh_terms: D000465:Algorithms; D002138:Calibration; D004784:Environmental Monitoring; D008401:Gas Chromatography-Mass Spectrometry / Q000592:standards; D019015:Geologic Sediments / Q000032:analysis* / Q000737:chemistry; D006358:Hot Temperature; D016018:Least-Squares Analysis; D009930:Organic Chemicals / Q000032:analysis* / Q000592:standards; D013997:Time Factors
chemical_list: D009930:Organic Chemicals
keywords: Chemometric analyses; Gas chromatography/mass spectrometry; Organic matter; Pyrolysis; Sediment; Sub-mg sample mass