in, 80–100 mesh, silco steel), followed by a Molsieve 5A column (10 ft x
in, 60–80 mesh, silco steel). Run conditions are isothermal at 50°C at 21 mL/min.
For hydrogen analyses, we used a 3800 Varian gas chromatograph equipped with three separate sample loops, three sets of columns, and three distinct detectors for gas analysis. Gas samples were withdrawn from the serum vial by piercing the solid rubber seal with a needle attached to a gas-tight glass syringe. The gas chromatograph was configured with argon as the carrier gas, an evacuated 1-mL sample loop, and a thermal conductivity detector (TCD). Helium and H2 are detected with the most sensitivity with detection limits of 2 parts per million (ppm). Methane is detected in concentrations above 20 parts per million by volume (ppmv). The TCD sample arm is controlled by a Type 4 electronic flow controller and is fed by a sample loop that uses two columns in series, a Hayesep R column (4 ft x
in, 80–100 mesh, silco steel), followed by a Molsieve 5A column (10 ft x
in, 60–80 mesh, silco steel). Run conditions are isothermal at 50°C at 21 mL/min.
Measurements on replicate sediment samples generally have a precision of ~5%. Accuracy of the chromatographic analysis is estimated to be 2% based on comparison of standards, and the precision is ~2%.
Acetate ion concentration of extracted pore water was determined by high-performance liquid chromotagraphy using a Shimadzu VP series chromatograph with an ultraviolet-visual light detector (SVP-10AVP) set at 210 nm. IW samples were allowed to thaw at room temperature, and ~1 mL was transferred to autosampler vials for immediate analyses. Acetate was separated using two columns in series (Bio-Rad Aminex HPX-87H and Hamilton PRP X300) with a 0.016-N sulfuric acid eluent flowing at 0.6 mL/min. The retention time for acetate was 25.8 min under these conditions. Detection limits of these analyses were ~3 µM. Acetate concentrations were calculated based on peak height from a five-point standard calibration curve. Measurements on replicate sediment samples generally have a precision of ~2%. Accuracy of the chromatographic analysis is estimated to be 1% based on comparison of standards, and the precision is also ~1%.
