Carbon Isotope Measurement of Extremely Low Amounts of CH4: Application to Volcanic Gases from Satsuma-Iwojima, Japan

摘要

A preconcentration system attached to a GC/C/MS (gas chromatography/combustion/mass spectrometer) was developed to determine the carbon-isotope composition of methane in volcanic gases with extremely low concentration. With this system, we can analyze the carbon isotope ratio (13C/12C) of 0.7 - 6 nmol methane with a precision of ±1.6‰, unlike other conventional methods without preconcentration (150 - 1000 nmol CH4 with a precision of ±0.2‰). This system was test-ed with volcanic gas samples from Satsuma-Iwojima volcano, suggesting a mixture of magmatic and thermogenic origins for methane.