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| Techniques and Methods 10–C17 |
(15N/14N) and (18O/16O) Nitrate in Water: RSIL Lab Code 2900U.S. Geological Survey
By Kinga Révész and Karen Casciotti
Chapter 17
Section C, Stable Isotope-Ratio Methods
Book 10, Methods of the Reston Stable Isotope Laboratory
This report is available as a pdf.
The purpose of Reston Stable Isotope Laboratory (RSIL) lab code 2900 is to determine the δ(15N/14N), abbreviated as δ15N, and δ(18O/16O), abbreviated as δ18O, of nitrate (NO3-) in water. The δ15N and δ18N of dissolved NO3- are analyzed by conversion of NO3- to nitrous oxide (N2O), which serves as the analyte for mass spectrometry. A culture of denitrifying bacteria is used in the enzymatic conversion of NO3- to N2O, which follows the pathway shown in equation 1:
| NO3–→ NO2– → NO → 1/2 N2O | (1) |
Because the bacteria Pseudomonas aureofaciens and P. aureofaciens lack N2O reductive activity, the reaction stops at N2O, unlike the typical denitrification reaction, that goes to N2. After several hours, the conversion is complete, and the N2O is extracted from the vial, separated from water vapor by Nafion drier and from CO2 with a layered Mg(ClO4)2/Ascarite trap, and trapped in a small-volume trap immersed in liquid nitrogen. After the N2O is released, it is further purified by gas chromatography (GC) before introduction to the isotope-ratio mass spectrometer (IRMS). The IRMS is a Finnigan DeltaPlus continuous flow isotope-ratio mass spectrometer (CF-IRMS). It has a universal triple collector, consisting of two wide cups with a narrow cup in the middle; it is capable of simultaneously measuring mass/charge (m/z) of the N2O molecule 44, 45, and 46. The ion beams from these m/z values are as follows: m/z = 44 = N2O = 14N14N16O; m/z = 45 = N2O = 14N15N16O or 14N14N17O; m/z = 46 = N2O = 14N14N18O. The 17O contributions to the m/z 44 and m/z 45 ion beams are accounted for before δ15N values are reported.
Forward
Conversion Factors
Acronyms, and Abbreviations
Symbols
Summary of Procedure
Reporting Units and Operational Range
Reference Materials and Documentatione
Reference Materials Used, Storage Requirements, and Shelf Life
Documentation
Labware, Instrumentation, and Reagents
Sample Collection, Preparation, Analysis, Retention Times, and Disposal
Sample Containers, Preservation, and Handling Requirements
Sample Preparation and Time Requirements
Performing the Analysis and Time Requirements
Problematic Samples
Interferences
Troubleshooting and Bench Notes
Maintenance and Maintenance Records
Sample Retention Time and Disposal
Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance
Laboratory Information Management System for Light Stable Isotope (LIMS-LSI)
Quality-Control (QC) Samples
Acceptance Criteria for all QC Samples
Corrective Action Requirements
Responsible Parties for All QA/QC Functions for Procedures Covered in RSIL SOPs
Data Management and Records
Health, Safety, and Waste-Disposal Information
Applicable Health and Safety Issues
Personal Protection
Electrical Hazards
Chemical Hazards
Gas Cylinder Handling
Biological Hazard
Specific Waste-Disposal Requirements
Revision History
References Cited
Apendixes
| A. | Step-by-Step Procedure to Log-in Samples to LIMS-LSI. |
| B. | Step-by-Step Procedure to Print a Template and a Samples-to-Be-Analyzed List. |
| C. | Step-by-Step Preparation Procedure for N Isotope Analyses of Nitrate by Bacterial Denitrification. |
| D. | Step-by-Step Procedure to Add Sample Information to Sequence Table. |
| E. | Step-by-Step Procedure to Transfer Data to LIMS-LSI, to Transfer Data to Back-Up Computer, and to Reevaluate Old Data. |
| F. | Step-by-Step Procedure to Determine and Apply Correction Factors and Evaluate Data. |
| G. | Daily Check List |
| H. | Step-by-Step Procedure to Report Data. |
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| U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/tm10c17 Page Contact Information: Publishing Service Center Last modified: Tuesday, August 14 2007, 03:53:22 PM |
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