Determination of the 15N/14N, 17O/16O, and 18O/16O ratios of nitrous oxide by using continuous-flow isotope-ratio mass spectrometry



We developed a rapid, sensitive, and automated analytical system to determine the δ15N, δ18O, and Δ17O values of nitrous oxide (N2O) simultaneously in nanomolar quantities for a single batch of samples by continuous-flow isotope-ratio mass spectrometry (CF-IRMS) without any cumbersome and time-consuming pretreatments. The analytical system consisted of a vacuum line to extract and purify N2O, a gas chromatograph for further purification of N2O, an optional thermal furnace to decompose N2O to O2, and a CF-IRMS system. We also used pneumatic valves and pneumatic actuators in the system so that we could operate it automatically with timing software on a personal computer. The analytical precision was better than 0.12‰ for δ15N with >4 nmol N2O injections, 0.25‰ for δ18O with >4 nmol N2O injections, and 0.20‰ for Δ17O with >20 nmol N2O injections for a single measurement. We were also easily able to improve the precision (standard errors) to better than 0.05‰ for δ15N, 0.10‰ for δ18O, and 0.10‰ for Δ17O through multiple analyses with more than four repetitions with 190 nmol samples using the automated analytical system. Using the system, the δ15N, δ18O, and Δ17O values of N2O can be quantified not only for atmospheric samples, but also for other gas or liquid samples with low N2O content, such as soil gas or natural water. Here, we showed the first ever Δ17O measurements of soil N2O. Copyright © 2008 John Wiley & Sons, Ltd.