Analysis of Lipids and Polycyclic Aromatic Hydrocarbons as Indicators of Past and Present (Micro)Biological Activity

Abstract

Analysis of lipids and hydrocarbons is performed frequently in recent and ancient plant tissues, soils, sediments, peat deposits, oil, rocks, anthropogenic artifacts (archeological samples), and other materials to trace the contribution of different biological and anthropogenic sources of organic matter as well as environmental changes and the fate of organic matter like degradation. The approaches for the analysis of lipids and hydrocarbons strongly vary from traditional methodologies like thin-layer chromatography to universal approaches like pyrolysis, whereas the preparative separation of lipid fractions based on their polarity enables gas-chromatographic analyses of single fractions and compound-specific analysis of stable (2H/1H, 13C/12C) and radioactive (14C) isotope compositions. Often, lipid extraction operationally defines a subfraction of total lipids. On the one hand, free extractable lipids are obtained by extraction with organic solvents, whereas on the other hand, total samples or extraction residues are extracted for more polar lipid fractions using highly polar organic solvents and water, to release bound lipids. Procedures for extraction of free extractable lipids are diverse and mainly defined by the target of research and availability of instrumentation. In the current protocol, state-of-the-art techniques for the investigation of free extract-able lipids in various materials are explained, which can be applied even in laboratory environments with limited technical equipment. The protocols cover sample preparation, extraction, purification, analysis, as well as a brief overview of the data evaluation using lipid molecular proxies and compound-specific isotopes. Metadata of the chapter that will be visualized online Often, lipid extraction operationally defines a subfraction of total lipids. On the one hand, free extractable lipids are obtained by extraction with organic solvents, whereas on the other hand, total samples or extraction residues are extracted for more polar lipid fractions using highly polar organic solvents and water, to release bound lipids. Also, procedures for extraction of free extractable lipids are diverse and mainly defined by the target of research and availability of instrumentation. In the current protocol, state-of-the-art techniques for the investigation of free extractable lipids in various materials are explained, which can be applied even in laboratory environments with limited technical equipment. The protocols cover sample preparation, extraction, purification, analysis, as well as a brief overview of the data evaluation using lipid molecular proxies and compound-specific isotopes. Keywords (separated by '-') Alkanes -Biomarkers -Fatty acids -Gas chromatography -Lipid extractionLipid fraction -Molecular proxies -Preparative separation -Solid-phase extraction purification, analysis, as well as a brief overview of the data evaluation using lipid molecular proxies and 21 compound-specific isotopes.22

Severe drought-influenced composition and δ13C of plant and soil n-alkanes in model temperate grassland and heathland ecosystems

“…For roots and shoots 0.5 − 2.0 g were extracted and 40 − 50 g for soil. Extraction time was at least 36 h (Wiesenberg and Gocke, 2017). After evaporation of the solvent under atmospheric conditions, the TLE concentration was determined gravimetrically.…”

“…Neutral lipid and fatty acid fractions were obtained after solid phase extraction with KOHcoated silica gel (Wiesenberg and Gocke, 2017). Neutral lipids were eluted with CH 2 Cl 2 followed by fatty acids, which were recovered with CH 2 Cl 2 /CH 2 O 2 (99:1; v:v).…”

“…Afterwards, lipid fractions were dried again and neutral lipids were further separated into aliphatic, aromatic and low polarity hetero compounds using a column filled with activated silica gel (100 Å). Aliphatic hydrocarbons were eluted with C 6 H 14 followed by aromatic hydrocarbons with C 6 H 14 /CH 2 Cl 2 (1:1, v:v) and low polarity hetero compounds with CH 2 Cl 2 /CH 3 OH (93:7, v:v; Wiesenberg and Gocke, 2017). Volume reduction was performed via rotary evaporation.…”

The fate of plant wax lipids in a model forest ecosystem under elevated CO2 concentration and increased nitrogen deposition

“…Plant biomass and soil fractions were extracted with a mixture of dichloromethane (DCM)/MeOH (9/1; v/v) using microwave extraction for 1 h at 1600 W (MARS Xpress TM Microwave Reaction System; CEM Corporation, Matthews, NC, USA). Solid phase extraction with silica gel and 5% KOH (Silica 60 + 5% KOH, 63-200 µm, Margot Köhnen-Willsch, Jülich, Germany) was used to separate each extract into neutral and acidic lipids (Wiesenberg and Gocke, 2016). First, neutral lipids were eluted with DCM and acidic lipids with DCM/HCO2H (99/1; v/v).…”

“…The aliphatic hydrocarbon fraction containing n-alkanes was eluted with hexane. The fraction was reduced in volume, transferred to a vial and stored dry until analysis (Wiesenberg and Gocke, 2016).…”