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

We developed a rapid, sensitive, and automated analytical system to determine the δ 15 N, δ 18 O, and Δ 17 O values of nitrous oxide (N 2 O) 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 N 2 O, a gas chromatograph for further purification of N 2 O, an optional thermal furnace to decompose N 2 O to O 2 , 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 δ 15 N with >4 nmol N 2 O injections, 0.25‰ for δ 18 O with >4 nmol N 2 O injections, and 0.20‰ for Δ 17 O with >20 nmol N 2 O injections for a single measurement. We were also easily able to improve the precision (standard errors) to better than 0.05‰ for δ 15 N, 0.10‰ for δ 18 O, and 0.10‰ for Δ 17 O through multiple analyses with more than four repetitions with 190 nmol samples using the automated analytical system. Using the system, the δ 15 N, δ 18 O, and Δ 17 O values of N 2 O can be quantified not only for atmospheric samples, but also for other gas or liquid samples with low N 2 O content, such as soil gas or natural water. Here, we showed the first ever Δ 17 O measurements of soil N 2 O. Copyright © 2008 John Wiley & Sons, Ltd.