Study on Accelerated Solvent Extraction of Free Fatty Acids in Marine Sediments

Fatty acids are one of the most abundant lipid markers in marine sediments, whose primary occurrence forms are free fatty acids and conjugated fatty acid. Free fatty acid can be extracted directly by solvent, and conjugated fatty acid is extracted from leftover sediment residue after free fatty acid has been extracted, through adding acid or alkali, and then extracting after being heated. Accelerated solven extraction (ASE) is a very popular method in the study of fatty acids due to its low cost and low toxicity. In this study, coastal sediments were collected from the East China Sea. Conjugated fatty acid is not suitable for verifying the method due to its low concentration and large uncertainty; therefore, the determination of free fatty acid in marine sediments by gas chromatography mass spectrometry with ASE for sample pretreatment is discussed in this paper. The main factors which affect the extraction yield of fatty acid by ASE, such as the proportion of extractants, the temperature, static extraction time and cycle times are discussed and optimized. The following conclusions were reached: methanol-methylene chloride (V:V=1:3) is more suitable to be the extractant. The extraction efficiency of different types of fatty acids varies with increasing temperature, static extraction time and cycle times. Based on increasing carbons being extracted and the highest extraction efficiency, the optimum parameters for fatty acid extraction from marine sediments are: extraction temperature of 110℃, static time of 10 min and 3 cycles. The precisions of this method were 3% to 23% RSD, and the recovery rates were from 72.2% to 104.6%. This method is applicable to the quantitative analysis of alcohols and ketones in marine sediment, which is an improvement on conventional soxhlet extraction with less reagent consumption, good precision and is a simple procedure.