The instrument is a mass spectrometer, modified for use to determine isotopic ratios of carbon12/carbon13 in either carbon dioxide (CO2) or methane (CH4).

For methane, the CO2 and carbon monoxide (CO) is removed from the sample through liquid nitrogen cryotraps and heaters. The remaining CH4 is converted to CO2 through heating and carried through to a mass spectrometer for analysis of masses 44,45 and 46, so the only remaining CO2 is from the converted CH4.

Sampling frequency is discrete with a precision of ~0.05 per mil. See documents for more detailed information about the instrument.