Optimization of automated gas sample collection and isotope ratio mass spectrometric analysis of delta C-13 Of CO2 in air

The application of C-13/C-12 in ecosystem-scale tracer models for CO2 in air requires accurate measurements of the mixing ratios and stable isotope ratios Of CO2. To increase measurement reliability and data intercomparability, as well as to shorten analysis times, we have improved an existing field sampling setup with portable air sampling units and developed a laboratory setup for the analysis of the delta C-13 Of CO2 in air by isotope ratio mass spectrometry (IRMS). The changes consist of (a) optimization of sample and standard gas flow paths, (b) additional software configuration, and (c) automation of liquid nitrogen refilling for the cryogenic trap. We achieved a precision better than 0.1 parts per thousand and an accuracy of 0.11 +/- 0.04 parts per thousand for the measurement of delta C-13 Of CO2 in air and unattended operation of measurement sequences up to 12h. Copyright (C) 2008 John Wiley & Sons, Ltd.