RAPID O-18 ANALYSIS OF CO2 SAMPLES BY CONTINUOUS-FLOW ISOTOPE RATIO MASS-SPECTROMETRY

Continuous-flow isotope ratio mass spectrometry (CF-IRMS) has been sho wn to minimize sample preparation and reduce the sample size requireme nts and time for the determination of carbon and nitrogen. An inexpens ive CF inlet was developed for the determination of the O-18 isotopic abundance in CO2. Initial efforts were hampered by significant exchang eable oxygen within the inlet system, which was minimized by design ch anges and post-analysis mathematical correction. The system was tested for accuracy in the measurement of O-18 abundance in standards and wa s accurate to 0.04 parts per thousand, with a precision of 0.03 parts per thousand. Additional tests were performed using urinary water for the measurement of energy expenditure by the doubly labeled water meth od and the results agreed to within 1% with those from traditional off -line, dual-inlet IRMS. The CF-IRMS reduced the analysis time to 2 min per sample compared with 15 min for traditional duel-inlet IRMS. (C) 1997 John Wiley & Sons, Ltd.