A Gas Chromatographic Separation for the H and C Stable Isotope Ratio Determination of Coal Compounds

A new, completely automated gas chromatography technique has been developed to separate the different gaseous compounds produced during underground coal gasification for their 13C/12C and D/H isotope ratio measurements. The technique was designed for separation and collection of H2, CO, CO2, H2O, H2S, CH4, and heavier hydrocarbons. These gaseous compounds are perfectly separated by the gas-phase chromatograph and quantitatively sent to seven combustion and collection lines. H2, CO, CH4, and heavier hydrocarbons are quantitatively oxidized to CO2 and/or H2O. The isotopic analyses are performed by the sealed-tube method. The zinc method is used for reduction of both water and H2S to hydrogen for D/H analysis. Including all preparation steps, the reproducibility of isotope abundance values, for a quantity higher than or equal to 0.1 mL of individual components in a mixture (5 mL of gases being initially injected in the gas chromatograph), is ±0.1‰ for δ13CPDB and ±6‰ for δDSMOW.