Micro GC H2S quantification
An Agilent 490 Micro GC (Agilent Technologies, Palo Alto, CA, USA) equipped with parallel Molsieve 5A and PoraPLOT U columns and a thermal conductivity detector was used for H2S analysis with Helium carrier gas (15PSI). The column and injector temperatures were isothermally set to 60 °C for the duration of the 120 s run. The injector was set to split mode with an injection time of 40 ms and a backflush time of 10 s. H2S standards were prepared as previously described66 where, briefly, H2S was generated by reacting Na2S (Sigma-Aldrich, Saint Louis, MO, USA) with excess HCl (Fisher) in a 20 ml Hungate bottle with a butyl rubber stopped in the anaerobic chamber. Six working calibration standards at concentrations corresponding to 25, 50, 100, 250, 750, and 1,500 ppm of H2S were prepared by diluting from a 5 µmol/ml stock. Either a 2 ml headspace of standard or the microcosm samples was withdrawn and injected into the instrument with a gas syringe. Standards were run in triplicate to create a calibration curve while the biological samples were each run once.