The headspace gas samples were collected through the butyl
rubber stoppers by means of a gas-tight syringe for GC analysis.
Headspace gas samples were analysed in a gas chromatographer
(Varian CP 3800) equipped with a thermal conductivity detector
(TCD). H2 and CO2 analysis was performed using a stainless steel
column (1/800 3), packed with Porapak S (Waters Corp., USA),
and N2 as carrier gas (flow rate of 11 mL/min). The GC column
was kept at 30–60 C, the injector at 60 C and the TCD at 150 C.