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Techniques and Methods 10–C5

Determination of the (¹⁵N/¹⁴N) and (¹³C/¹²C) of Total N and C in Solids: RSIL Lab Code 1832

U.S. Geological Survey

By Kinga Révész and Haiping Qi

This report is available as a pdf.

Summary of Procedure

The purpose of Reston Stable Isotope Laboratory (RSIL) lab code 1832 is to determine the δ¹⁵N and δ¹³C of total nitrogen and carbon in a solid sample. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen and carbon in a solid sample into N₂ and CO₂ gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines the relative difference in stable nitrogen isotope–amount ratio (¹⁵N/¹⁴N) of the product N₂ gas and the relative difference in stable carbon isotope–amount ratio (¹³C/¹²C) of the product CO₂ gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in tin capsules and loaded into a Costech Zero-Blank Autosampler on the EA. Under computer control, samples then are dropped into a heated reaction tube that contains an oxidant, where combustion takes place in a He atmosphere containing an excess of oxygen gas. Combustion products are transported by a He carrier through a reduction furnace to remove excess oxygen and to 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 (GC). The gas is then introduced into the IRMS through a Finnigan ConFlo II interface. The ConFlo II interface is used for introducing not only sample into the IRMS but also N₂ and CO₂ reference gases and He for sample dilution. The flash combustion is quantitative; no isotopic fractionation is involved. The IFMS is a Finnigan Delta^Plus CF-IRMS. It has a universal triple collector, two wide cups and a narrow cup in the middle; it is capable of measuring mass/charge (m/z) 28, 29, 30 or with a magnet current change 44, 45, and 46 simultaneously. The ion beams from these m/z values are as follows: m/z 28 = N₂ = ¹⁴N¹⁴N; m/z 29 = N₂ = ¹⁴N¹⁵N primarily; m/z 30 = N0 = ¹⁴N¹⁶O primarily, which is a sign of contamination or incomplete reduction; m/z 44 = CO₂ = ¹²C¹⁶O¹⁶O; m/z 45 = CO₂ = ¹³C¹⁶O¹⁶O primarily; m/z 46 = CO₂ = ¹²C¹⁶O¹⁸O primarily.

Table of Contents

Preface

Conversion Factors, Acronyms, and Abbreviations

Summary of Procedure

Reporting Units and Operational Range

Reference Materials and Documentation

Reference Materials Used, Storage Requirements, and Shelf Life

Documentation

Labware, Instrumentation, and Reagents

Sample Collection, Preparation, Analysis, Holding 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

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 Generate an Excel Sample Workbook or to Print a Template and a Sample to Be Analyzed List
C.	Step-by-Step Procedure for Weighing and Storing Samples
D.	Step-by-Step Procedure for Zero Blank Auto Sampler Operation
E.	Step-by-Step Procedure to Add Sample Information to Sequence Table
F.	Step-by-Step Procedure to Retrieve Data from ISODAT 2.0 for LIMS-LSI and for Data Back-Up
G.	Step-by-Step Procedure to Transfer Data to LIMS-LSI, to Transfer Data to Back-Up Computer, and to Reevaluate Old Data
H.	Step-by-Step Procedure to Determine and Apply Correction Factors and Evaluate Data
I.	Step-by-Step Procedure to Check Elemental Analyzer for Leaks
J.	Daily Check List
K.	Changing the Insertion Tube
L.	Changing the Water-Trap
M.	Changing the Reaction Tube
N.	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/tm10c5 Page Contact Information: Publishing Service Center Last modified: Tuesday, August 14 2007, 04:03:01 PM

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