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UC Davis Plant Sciences


Nitrate (NO3) Analysis by Bacteria Denitrification

The SIF provides the preparation and isotope analysis (15N, 18O) of NO3 in water by bacteria denitrification assay.

Analysis of 15N and 18O of N2O from NO3 by bacterial denitrification assay
Isotope ratios of 15N and 18O are measured using a ThermoFinnigan GasBench + PreCon trace gas concentration system interfaced to a ThermoScientific Delta V Plus isotope-ratio mass spectrometer (Bremen, Germany). Gas samples are purged from vials through a double-needle sampler into a helium carrier stream (25 mL/min).  The gas sample passes through a CO2 scrubber (Ascarite) and N2O is trapped and concentrated in two liquid nitrogen cryo-traps operated in series such that the N2O is held in the first trap until the non-condensing portion of the sample gas has been replaced by helium carrier, then passed to the second, smaller trap. Finally, the second trap is warmed to ambient, and the N2O is carried by helium to the IRMS via an Agilent GS-Q capillary column (30m x 0.32 mm, 40°C, 1.0 mL/min). This column separates N2O from residual CO2. A reference N2O peak is used to calculate provisional isotope ratios of the sample N2O peak.

Final δ15N values are calculated by adjusting the provisional values such that correct δ15N values for laboratory reference materials are obtained. The calibration standards are the nitrates USGS 32, USGS 34, and USGS 35, supplied by NIST (National Institute of Standards and Technology, Gaithersburg, MD).  Additional laboratory reference materials are included in each batch to monitor and correct for instrumental drift and linearity. 

 


Limit of Quantitation and Long-term standard deviation for 15N and 18O of N2O from NO3 by bacterial denitrification

Limit of Quantitation: 2 μM NO3 in water

Accepted Precision: 0.4 ‰ for 15N

                                     0.5 ‰ for 18O









 
e-mail: sif@ucdavis.edu | phone: 530-752-8100 | fax: 530-752-4361
UC Davis Stable Isotope Facility | Department of Plant Sciences
One Shields Avenue | Davis, California, 95616 | USA