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Isolation of Individual Saturated Fatty Acid Methyl Esters Derived From Groundwater Phospholipids by Preparative High‐Pressure Liquid Chromatography for Compound‐Specific Radiocarbon Analyses
Author(s) -
Schwab Valérie F.,
Nowak Martin E.,
Trumbore Susan E.,
Xu Xiaomei,
Gleixner Gerd,
Muhr Jan,
Küsel Kirsten,
Totsche Kai U.
Publication year - 2019
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr024076
Subject(s) - chromatography , high performance liquid chromatography , extraction (chemistry) , chemistry , gas chromatography , environmental chemistry
Determining the biogeochemical pathways utilized by microbes living in groundwater is essential for understanding the subsurface C cycle and the fate of organic compounds, including pollutants. The radiocarbon signature (Δ 14 C) of fatty acid methyl esters derived from microbial phospholipids (PLFA) provides useful information for differentiating microbial C sources and infering microbial metabolism. However, in subsurface environments, those analyses remain challenging. Here we present a method combining large volume groundwater filtration (up to 10,000 L) and PLFA purification for subsequent compound‐specific radiocarbon analyses. The analytical method involves conventional chemical extraction of PLFA followed by purification of individual compounds by semipreparative high‐performance liquid chromatography. Different saturated PLFA in amounts of up to 10 μg each can be simultaneously separated on a C 18 high‐load column using a mixture of MeOH/water and acetonitrile as the mobile phase. Our procedure introduced dead‐C ext contaminations of 0.57 ± 0.29 and 0.35 ± 0.18 μg for the high‐performance liquid chromatography and combustion/graphitization steps of the sample preparation, respectively. However, tests on different high‐performance liquid chromatography C 18 columns revealed a large difference in dead C ext associated with column bleed. Modern C ext in the amount of 0.40 ± 0.20 μg was introduced by the combustion/graphitization step of the sample preparation, but other steps did not add modern C ext. The entire method recovered ∼50% of the purified compounds on average, but this did not affect their 14 C content. This method will allow routine analysis of the Δ 14 C of PLFA isolated from groundwaters or other sample types, revealing the relationships between microbial and soil‐derived C, sedimentary or dissolved C sources.