Comparing lipid extraction methods on lake sediments without dichloromethane

Abstract

This study compares different lipid extraction methods and solvents with a focus on reducing or eliminating the use of dichloromethane (DCM). DCM has high neurotoxicity and is carcinogenic. This study focuses on lake sediment extraction using accelerated solvent extraction (ASE), sonication, QuEChERS, and Soxhlet methods and compares the solvents DCM, ethyl acetate (EtOAc), methanol (MeOH), and hexanes. For ASE and sonication extractions, the replacement of DCM with EtOAc results in similar extraction efficiencies for n-alkanes, n-alkanols, and slightly lower extraction of n-alkanoic acids. For example, when using an ASE with recovery standards, switching from 9:1 DCM/MeOH to 9:1 EtOAc/MeOH results in a small decrease of 10% in the extraction of total hydrocarbons (mostly n-alkanes), the same recovery of the alcohols (mostly n-alkanols), and a decrease of 19% for the acids (mostly n-alkanoic acids). The QuEChERS method reduces the volume of DCM, but had poor recovery compared to ASE or sonication. Many labs could switch from using DCM to EtOAc with ASE or sonication and have minor to no changes in extraction efficiency. The use of 9:1 hexanes/EtOAc produced high recoveries of n-alkanes and n-alkanols with a cleaner extract that requires less post extraction cleanup. Sonication has the potential advantage of higher throughput and lower costs, although hands-on time is higher than ASE and recoveries were not always as high as with ASE. While this study focuses on the extraction of lake sediment, the results should be transferable to the extraction of soils, rocks, and other biological materials with minor method adjustments.