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Techniques and Methods 10–C11

Determination of the δ15N of Total Nitrogen in Solids; RSIL Lab Code 2893

By Kinga Révész, Haiping Qi, and Tyler B. Coplen

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The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2893 is to determine the δ(15N/14N), abbreviated as δ15N , of total nitrogen in solid samples. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen in a solid sample into N2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines relative difference in the isotope-amount ratios of stable nitrogen isotopes (15N/14N)of the product N2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in a tin capsule and loaded into the Costech Zero Blank Autosampler of the EA. Under computer control, samples are dropped into a heated reaction tube that contains an oxidant, where the combustion takes place in a helium atmosphere containing an excess of oxygen gas. Combustion products are transported by a helium carrier through a reduction tube to remove excess oxygen and convert all nitrous oxides into N2 and through a drying tube to remove water. The gas-phase products, mainly CO2 and N2, are separated by a gas chromatograph. The gas is then introduced into the isotope-ratio mass spectrometer (IRMS) through a Finnigan MAT (now Thermo Scientific) ConFlo II interface, which also is used to inject N2 reference gas and helium for sample dilution. The IRMS is a Thermo Scientific Delta V Plus CF-IRMS. It has a universal triple collector, two wide cups with a narrow cup in the middle, capable of measuring mass/charge (m/z) 28, 29, 30, simultaneously. The ion beams from N2 are as follows: m/z 28 = N2 = 14N14N; m/z 29 = N2 = 14N15N primarily; m/z 30 = NO = 14N16O primarily, which is a sign of contamination or incomplete reduction.

Revised September 17, 2012 (version 1.2)

First posted 2006 and revised 2007

For additional information contact:
Director, Reston Stable Isotope Laboratory
U.S. Geological Survey
12201 Sunrise Valley Drive, MS 431
Reston, VA 20192
http://isotopes.usgs.gov/

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Suggested citation:

Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ15N of total nitrogen in solids; RSIL lab code 2893, chap. 11 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 30 p., available only at http://pubs.usgs.gov/tm/2006/tm10c11/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)



Contents

Foreword

Summary of Procedure

Reporting Units and Operational Range

Reference Materials and Documentation

Labware, Instrumentation, and Reagents

Sample Collection, Preparation, Analysis, Retention Times, and Disposal

Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance

Health, Safety, and Waste-Disposal Information

Revision History

References Cited

Appendix A. Step-by-Step Procedure to Log-In Samples to LIMS-LSI

Appendix B. Step-by-Step Procedure to Create an Excel Sample-List Workbook and Print a Sample List

Appendix C. Step-by-Step Procedure for Weighing and Storing Samples
Appendix D. Step-by-Step Procedure of Zero Blank Autosampler Operation
Appendix E. Step-by-Step Procedure to Add Sample Information to Sequence Table
Appendix F. Step-by-Step Procedure to Retrieve Data from ISODAT 2.0 for LIMS-LSI and for Data Back-Up
Appendix G. Step-by-Step Procedure to Transfer Data to LIMS-LSI, to Transfer Data to Back-Up Computer, and to Reevaluate Old Data
Appendix H. Step-by-Step Procedure to Determine and Apply Correction Factors and Evaluate Data
Appendix I. Step-by-Step Procedure to Check Elemental Analyzer for Leaks
Appendix J. Daily Checklist


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