A simplified technique for collecting breath CO2 for isotope ratio mass spectrometry.

A simplified technique of collecting breath CO2 for isotopic analysis has been developed. The subject breathes into a 3 1 bag from which a 50 ml aliquot is transferred to an evacuated, septum-capped tube (Vacutainer). The sample is later withdrawn and the CO2 is cryogenically purified. No isotope fractionation is observed in samples collected in this manner. Samples have been stored up to three months without any change in the isotope ratio.