Table 1.

Comparison of δ¹³C values for methane, ethane, and propane run individually on the GC-C-IRMS (2.5-μL injection; split ratio 1:30) and the GC-C-CRDS (25 μL, splitless)

Compound	GC-C-IRMS δ13C, ‰, individual components	GC-C-CRDS δ13C, ‰, individual components	GC-C-CRDS δ13C, ‰, from mixture
Methane	−44.07 ± 0.46	−47.16 ± 0.68	−45.76 ± 0.61
Ethane	−37.68 ± 0.41	−39.63 ± 0.89	−36.15 ± 0.86
Propane	−39.57 ± 0.20	−39.57 ± 0.82	−38.75 ± 1.04

The GC-C-CRDS individual component amounts are calibrated to have the same value for propane as for GC-C-IRMS. Also shown are the results from running a 75-μL mixture of approximately equal amounts of methane, ethane, and propane on the GC-C-CRDS. These results have not been calibrated with the measurements obtained using GC-C-IRMS. Owing to variations in the sample preparation process, differences in isotopic composition between samples run individually and as a mixture are expected. Errors represent 1 standard deviation based on 5 measurements in each case.