Automated simultaneous measurement of the δ13C and δ2H values of methane and the δ13C and δ18O values of carbon dioxide in flask air samples using a new multi cryo-trap/gas chromatography/isotope ratio mass spectrometry system

RATIONALE: The isotopic composition of greenhouse gases helps to constrain global budgets and to study sink and source processes. We present a new system for high-precision stable isotope measurements of carbon, hydrogen and oxygen in atmospheric methane and carbon dioxide. The design is intended for analyzing flask air samples from existing sampling programs without the need for extra sample air for methane analysis. METHODS: CO, and CH4 isotopes are measured simultaneously using two isotope ratio mass spectrometers, one for the analysis of delta C-13 and delta O-18 values and the second one for delta H-2 values. The inlet carousel delivers air from 16 sample positions (glass flasks 1-5 L and high-pressure cylinders). Three 10-port valves take aliquots from the sample stream. CH4 from 100-mL air aliquots is preconcentrated in 0.8-mL sample loops using a new cryo-trap system. A precisely calibrated working reference air is used in parallel with the sample according to the Principle of Identical Treatment. RESULTS: It takes about 36 hours for a fully calibrated analysis of a complete carousel including extractions of four working reference and one quality control reference air. Long-term precision values, as obtained from the quality control reference gas since 2012, account for 0.04 parts per thousand (delta C-13 values of CO2), 0.07 parts per thousand (delta O-18 values of CO2), 0.11 parts per thousand (delta C-13 values of CH4) and 1.0 parts per thousand (delta H-2 values of CH4). Within a single day, the system exhibits a typical methane delta C-13 standard deviation(1 sigma) of 0.06 parts per thousand for 10 repeated measurements. CONCLUSIONS: The system has been in routine operation at the MPI-BGC since 2012. Consistency of the data and compatibility with results from other laboratories at a high precision level are of utmost importance. A high sample throughput and reliability of operation are important achievements of the presented system to cope with the large number of air samples to be analyzed. Copyright (C) 2016 John Wiley & Sons, Ltd.