Measurement of volatile fatty acids in pore water from marine sediments by HPLC

Abstract

Lower molecular weight volatile fatty acids are important intermediates in the anaerobic degradation of organic matter in marine sediments. The analysis of these compounds at the low in situ concentrations, however, still presents difficulties. A new derivatization procedure for the analysis of these compounds, coupled with high-performance liquid chromatography, has been modified for the analysis of volatile fatty acids in marine pore water to cover a linear calibration range from 0·5 μ m to 10 m m. The modifications resulted in the detection of concentrations 40 times lower than in the original method and in good recoveries of fatty acid standards added to pore water (mean 101%). This modified procedure was then used to analyse fatty acids in pore water from sediments along a gradient of organic enrichment. The relative ratios of the individual acids were 1:0·1:0·02:0·01:0·02:0·01 for acetate, propionate, n-butyrate 2-methylbutyrate, iso-valerate and n-valerate. There was a tendency for the concentration of the more reduced acids to increase (propionate and n-butyrate) as organic enrichment increased. Several fatty acids were found that have not commonly been reported in marine pore water. These include 2-methylbutyrate, which is a specific anaerobic degradation product of iso-leucine, which, to the authors' knowledge, has not been previously found in marine pore water.