Compound identification and molecular abundance distribution of long-chain n-alkanes from a peat sequence in the middle Yangtze river catchment, southeast China

The samples from our peat core were collected using a manual sampling drill and PVC tubes with a diameter of 0.60m. The sampling site is located at Xiyaohu(XYH) peatland (28.44°N, 115.40°E, elevation: 735m). The penetration length is 3.35m, and the total length of the core is 3.00m. From 2016-9 to 2016-11, the core was subsampled at 5- and 4-cm intervals through the top and bottom 0.15m, respectively .The leaf-wax n-alkanes were freeze-dried and homogenized. Sediments were solvent-extracted with 9:1 v/ v dichloromethane (DCM) to methanol (MeOH) at 30 °C for 30 min and 1500 psi for 5 min using an accelerated solvent extraction system. Total lipid extracts were separated using column chromatography through silica gels into the hexane and neutral fractions, using hexane and 9:1 v/v DCM: MeOH, respectively. The hexane and neutral fractions contain n-alkanes and the remaining parts of the lipid, such as long-chain ketene, respectively. From 2017-2 to 2017-4, compound identification and the molecular abundance distribution of long-chain n-alkanes were detected by gas chromatography (GC, Agilent 7890B) equipped with a flame ionization detector (FID) for separation and quantification. The FID temperature was 310 °C, the H2 speed was 30 mL/min, the airflow speed was 400 ml/min, and each sample tested was 1 µL. Individual n-alkane identification was performed by comparing the retention times of n-alkanes in samples with the aforementioned standards.