Theme: Coastal Systems I

4:00  Ava Kreider-Mueller –  Dartmouth – Title: A combined Ti(III)-Azide reducing reagent for the chemical conversion of nitrates to N2O for d15N isotopic analysis 
Author(s): Ava Kreider-Mueller & Mark A. Altabet

d15N isotopic analysis, which can be used to identify the sources and monitor the fate of nitrate (NO3–) in ecosystems, has proven to be an effective tool for use in the study of terrestrial and marine nitrogen cycles. Although there are several well established methods designed to reduce environmental NO3– to nitrous oxide (N2O) for analysis by continuous flow-isotope ratio mass spectrometry (CF-IRMS), such methods typically require the use of toxic chemicals, involve arduous laboratory preparations, or result in the production of multiple end products that lower the reaction yield. We developed a new, combined Titanium(III)-Azide (Ti-Azide) reducing reagent for the quantitative conversion of NO3– to N2O, which is accomplished in one procedural step with reproducible reaction yields and reliably accurate d15N measurements. The reagent is easily prepared from inexpensive chemical components, and samples can be prepared within a few minutes. Herein we describe the results of a time-series test and an experimental matrix that were designed to identify the optimal method of sample preparation that ensures the most reproducible d15N measurements and highest yields are obtained. To test the validity of the new method, we prepared a set of Line Island water samples using the Ti-Azide method as well as the previously established TiCl3 method and found that IRMS analysis gave comparable d15N results.