Isotopic Analysis of N and O in Nitrite and Nitrate by Sequential Selective Bacterial Reduction to N2O
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- 作者：John Karl Bö ; hlke ; Richard L. Smith ; Janet E. Hannon
- 刊名：Analytical Chemistry
- 出版年：2007
- 出版时间：August 1, 2007
- 年：2007
- 卷：79
- 期：15
- 页码：5888 - 5895
- 全文大小：148K
- 年卷期：v.79,no.15(August 1, 2007)
- ISSN：1520-6882
文摘
Nitrite is an important intermediate species in the biogeochemical cycling of nitrogen, but its role in naturalaquatic systems is poorly understood. Isotopic data canbe used to study the sources and transformations of NO2-in the environment, but methods for independent isotopicanalyses of NO2- in the presence of other N species arestill new and evolving. This study demonstrates thatisotopic analyses of N and O in NO2- can be done bytreating whole freshwater or saltwater samples with thedenitrifying bacterium Stenotrophomonas nitritireducens, which selectively reduces NO2- to N2O forisotope ratio mass spectrometry. When calibrated withsolutions containing NO2- with known isotopic compositions determined independently, reproducible 
15N and18O values were obtained at both natural-abundancelevels (±0.2-0.5” for 15N and ±0.4-1.0” for 18O)and moderately enriched 15N tracer levels (±20-50” for15N near 5000”) for 5-20 nmol of NO2- (1-20
mol/L in 1-5 mL aliquots). This method is highlyselective for NO2- and was used for mixed samplescontaining both NO2- and NO3- with little or no measurable cross-contamination. In addition, mixed samples thatwere analyzed with S. nitritireducens were treatedsubsequently with Pseudomonas aureofaciens to reducethe NO3- in the absence of NO2-, providing isotopicanalyses of NO2- and NO3- separately in the same aliquot.Sequential bacterial reduction methods like this oneshould be useful for a variety of isotopic studies aimed atunderstanding nitrogen cycling in aquatic environments.A test of these methods in an agricultural watershed inIndiana provides isotopic evidence for both nitrificationand denitrification as sources of NO2- in a small stream.
15N and18O values were obtained at both natural-abundancelevels (±0.2-0.5” for 15N and ±0.4-1.0” for 18O)and moderately enriched 15N tracer levels (±20-50” for15N near 5000”) for 5-20 nmol of NO2- (1-20mol/L in 1-5 mL aliquots). This method is highlyselective for NO2- and was used for mixed samplescontaining both NO2- and NO3- with little or no measurable cross-contamination. In addition, mixed samples thatwere analyzed with S. nitritireducens were treatedsubsequently with Pseudomonas aureofaciens to reducethe NO3- in the absence of NO2-, providing isotopicanalyses of NO2- and NO3- separately in the same aliquot.Sequential bacterial reduction methods like this oneshould be useful for a variety of isotopic studies aimed atunderstanding nitrogen cycling in aquatic environments.A test of these methods in an agricultural watershed inIndiana provides isotopic evidence for both nitrificationand denitrification as sources of NO2- in a small stream.