|Title||Fully automated, high-precision instrumentation for the isotopic analysis of tropospheric N2O using continuous flow isotope ratio mass spectrometry.|
|Year of Publication||2013|
|Authors||Potter KE, Ono S, Prinn RG|
RATIONALE: Measurements of the isotopic composition of nitrous oxide in the troposphere have the potential to bring new information about the uncertain N2 O budget, which mole fraction data alone have not been able to resolve. Characterizing the expected subtle variations in tropospheric N2 O isotopic composition demands high-precision and high-frequency measurements. To enable useful observations of N2 O isotopic composition in tropospheric air to reduce N2 O source and sink uncertainty, it was necessary to develop a high-precision measurement system with fully automated capabilities for autonomous deployment at remote research stations. METHODS: A fully automated pre-concentration system for high-precision measurements of N2 O isotopic composition (δ(15) N(β) , δ(15) N(α) , δ(18) O) in tropospheric air has been developed which combines a custom liquid-cryogen-free cryo-trapping system and gas chromatograph interfaced to a continuous flow isotope ratio mass spectrometry (IRMS) system. A quadrupole mass spectrometer was coupled in parallel to the IRMS system during development to evaluate peak interference. Multi-port inlet and fully-automated capabilities allow streamlined analyses between in situ air inlet, air standards, flask air sample, or other gas source in exactly replicated analysis sequences. RESULTS: The system has the highest precision to date for (15) N site-specific composition results (δ(15) N(α) ±0.11‰, δ(15) N(β) ±0.14‰ (1σ)), attributed mostly to uniformity of analytical cycles and particular attention to fluorocarbon interference noted for (15) N site-specific measurements by IRMS. Air measurements demonstrated the fully automated capacity and performance. CONCLUSIONS: The system makes substantial headway in measurement precision, possibly defining the limits of IRMS measurement capabilities in low concentration N2 O air samples, with fully automated capabilities to enable high-frequency in situ measurements. Copyright © 2013 John Wiley & Sons, Ltd.