Technical Updates to the Bacterial Method for Nitrate Isotopic Analyses

The bacterial conversion of aqueous nitrate (NO3-) to nitrous oxide (N2O) for isotopic analysis has found widespread use since its introduction (Sigman, D. M.; Casciotti, K. L.; Andreani, M.; Galanter, M.; Bohlke, J. K. Anal, Chem. 2001, 73, 4145-4153; Casciotti, K. L.; Sigman, D. M.; Galanter Hastings, M.; Bohlke, J. K; Hilkert, A. Anal. Chem. 2002, 74, 4905-4912). The bacterial strain Pseudomonas aureofaciens (ATTC no. 13985) was shown to convert NO3- to N2O while retaining both N and O isotopic signatures, and automation of the isotopic analysis of N2O greatly increased the throughput of the method (Casciotti, K. L.; Sigman, D. M.; Galanter Hastings, M.; Bohlke, J. K; Hilkert, A. Anal. Chem. 2002, 74, 4905-4912). Continued development of the denitrifier method has led to increased precision and throughput of NO3- isotopic analysis. Presented here are several recent procedural modifications and the demonstration of their effectiveness.