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A robust, simple and efficient gas chromatography (GC) method is presented for determining H2 and CH4 concentrations simultaneously in water samples. The GC system consists of one detector (pulsed discharge helium ionization detector-PDHID), two columns in two ovens, respectively, and two 2-position-6-port purge valves. In this method, H2 and CH4 in water samples were first extracted into the headspace of syringes, then injected into the GC system. Both H2 and CH4 were detected by a PDHID. The separation of CH4 from O2 and N2 in seawater is achieved by switching the O2 and N2 out of the carrier gas flow at the appropriate time window. H2 and CH4 concentrations in water samples collected from hydrothermal plumes at the Southwest Indian Ridge were determined successfully using this method. [ABSTRACT FROM AUTHOR]

Conversion of CO2 to organic compounds in hydrothermal systems is important in understanding prebiotic chemical evolution leading to the origin of life. However, organic compounds with carbon number of more than 3 have never been produced from dissolved CO2 in simulated hydrothermal experiments. In this paper, we report that not only CH4, C2H6 and C3H8, but also n-C4H10 and n-C5H12 could be produced from dissolved CO2 and H2 in the presence of cobalt-bearing magnetite at 300°C and 30 MPa. It is shown that unbranched alkanes in Anderson–Schulz–Flory distribution were the dominant hydrocarbon products produced from dissolved CO2 catalyzed by cobalt-bearing magnetite under certain hydrothermal conditions. It is proposed that magnetite with other transition metals may act potentially as effective mineral catalysts for abiotic formation of organic compounds from dissolved CO2 in hydrothermal systems. [ABSTRACT FROM AUTHOR]