2.3. Chemicalanalyses
Hydrogen, nitrogen, and methane were examined using a gas chromatograph (GC, model 2601B; SRI Instruments, CA) equipped with a 3-m Molsieve 5A 80/100 column (Altech Associates, Inc., Bannockburn, IL) with argon as carrier gas at 80 ◦ C. Carbon diox- ide was analyzed using a GC (model 310; SRI Instruments, CA) with a 1-m silica gel column (Restek Corporation, Bellefonte, PA) and helium as the carrier gas at 60◦C. Both GCs were equipped with thermal conductivity detectors (TCDs) with a detection limit of 0.01%. To examine metabolites excreted into solution, 1 mL of cathode solution was filtered through a 0.22-