Abstract
The analysis of the dissolved organic fraction of hydrothermal fluids has been considered a real challenge due to sampling difficulties, complexity of the matrix, numerous interferences and the assumed ppb concentration levels. The present study shows, in a qualitative approach, that Stir Bar Sorptive Extraction (SBSE) followed by Thermal Desorption – Gas Chromatography – Mass Spectrometry (TD-GC-MS) is suitable for extraction of small sample volumes and detection of a wide range of volatile and semivolatile organic compounds dissolved in hydrothermal fluids. In a case study, the technique was successfully applied to fluids from the Rainbow ultramafic-hosted hydrothermal field located at 36°14’N on the Mid-Atlantic Ridge (MAR). We show that n-alkanes, mono- and poly- aromatic hydrocarbons as well as fatty acids can be easily identified and their retention times determined. Our results demonstrate the excellent repeatability of the method as well as the possibility of storing stir bars for at least three years without significant changes in the composition of the recovered organic matter. A preliminary comparative investigation of the organic composition of the Rainbow fluids showed the great potential of the method to be used for assessing intrafield variations and carrying out time series studies. All together our results demonstrate that SBSE-TD-GC-MS analyses of hydrothermal fluids will make important contributions to the understanding of geochemical processes, geomicrobiological interactions and formation of mineral deposits.
Highlights
Organic geochemistry is of major importance in both geosciences and life sciences [1]
We show that Stir Bar Sorptive Extraction (SBSE) – Thermal Desorption – Gas Chromatography – Mass Spectrometry (TD-GC-MS) is an effective and reliable method capable of isolating a wide range of organic molecules from small sample volumes of the complex matrix that are hydrothermal fluids
Identification of compounds in hydrothermal fluids using standard mixtures Konn et al [13], successfully identified organic compounds in several hydrothermal fluid samples based on comparison with the NIST02 library associated with consistent retention times (Rt)
Summary
Organic geochemistry is of major importance in both geosciences and life sciences [1]. 4.8 min Figure 6 Zooms of extracted ion chromatograms at the qualifier ion m/z 104 (left) and m/z 91 (right) of the SBSE-TD-GC-MS analysis of 3 hydrothermal fluid samples (T10, T88, T92) and a deep seawater sample (T72). 4.0 min Figure 7 Zooms of extracted ion chromatograms at the qualifier ion m/z 91 of the SBSE-TD-GC-MS analysis of 3 hydrothermal fluid samples (T10, T88, T92) and a deep seawater sample (T72) (left panel); and 6 replicates of MQ water spiked with toluene at 10 μg/L (right panel). Unequivocal identification of individual organic compounds in hydrothermal fluids was possible using both the Rt of the standards and extracted ion chromatograms
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