To examine on accuracy for data in natural gases and cuttings ones, some problems on sampling vessels, preservation period of small amounts of gases for stable isotope mass spectrometry and carbon dioxide preparation were discussed.
As sampling containers, Tedlar bags, Teflon, polyethylene and glass were used. As the results, components in standard methane (δ¹³C: -65.4‰), changed to -58.2‰ in Tedlar bags, to -62.4‰ in Teflon, to -63.7‰ in polyethylene vessels, while not in glass vessels after one month. When production gas is used as a sample, the change of components showed same tendency as above.
Residual gases in carbon dioxide preparation stage, especially from preceding concentrated gases, affected much on successive determinations.
In ¹³C stable isotope ratio mass spectrometry, attentions should be on sampling vessels and on excluding residual gases in carbon dioxide preparation stage. Glass bottles are the most favourable for sampling and preservation of gases for the analysis.