Determination of the δ(

15N/14N) of 

Total Nitrogen in Solids: 

RSIL Lab Code 2893 

Chapter 11 of 

Book 10, Methods of the Reston Stable Isotope 

Laboratory 

Section C, Stable Isotope-Ratio Methods 

Techniques and Methods 10-C11 

U.S. Department of the Interior 

U.S. Geological Survey

Determination of the δ(

15N/14N) of 

Total Nitrogen in Solids: 

RSIL Lab Code 2893 

By Kinga Révész and Haiping Qi 

Chapter 11 of 

Book 10, Methods of the Reston Stable Isotope 

Laboratory 

Section C, Stable Isotope-Ratio Methods 

Edited by Kinga Révész and Tyler B. Coplen 

Techniques and Methods 10-C11 

U.S. Department of the Interior 

U.S. Geological Survey
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2006 

Revised July 2007 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products: 

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual copyright owners to

reproduce any copyrighted material contained within this report. 

Suggested citation: 

Révész, Kinga, Qi, Haiping, 2006, Determination of the δ(

15N/14N) of Total Nitrogen in Solids: RSIL Lab Code 2893 

chap. C11 of Révész, Kinga, and Coplen, Tyler B., eds., Methods of the Reston Stable Isotope Laboratory: Reston, 

Virginia, U.S. Geological Survey, Techniques and Methods, book 10, sec. C, chap. 11, 31 p. 
Foreword 

The Reston Stable Isotope Laboratory (RSIL) provides stable isotope analyses on a routine basis 

for a large user community within the U.S. Geological Survey (USGS) and elsewhere. The RSIL 

also serves the USGS National Research Program (NRP) through its project on Stable Isotope 

Fractionation in Hydrologic Processes. The NRP conducts basic and problem-oriented hydrologic 

research in support of the mission of the USGS. The stable isotope project conducts research on

the use of isotope-ratio measurements in studies of water resources and environmental quality. 

One objective of this project is to develop new techniques for isotopic analysis of H, N, O, C, and 

S in environmental samples. New analytical techniques expand the range of tools available for 

studying the movement of those elements in hydrologic and biogeochemical systems. Another 

objective of the project is to test new applications of isotope measurements in specific field 

settings. Field studies of isotope behavior have contributed to understanding of water-supply 

sustainability, ground-water/surface-water interactions, paleoclimate history, biologic cycling of 

nutrients, ground-water contamination, and natural remediation. This project also contributes to 

the improvement of measurement science and the development of isotope databases. 

Book 10 of the Techniques and Methods Series of the USGS contains detailed descriptions of 

methods of the RSIL, including routine analytical methods called standard operating procedures 

(SOPs), along with safety guidelines, maintenance procedures, and other information about the 

operation of the RSIL. Section C of Book 10 contains the SOPs for a variety of methods to 

measure stable isotope ratios, each of which constitutes a chapter. Each chapter is limited to a 

narrow field of subject matter to permit flexibility in revision as the need arises. 

Pierre Glynn 

Chief, Branch of Regional Research, Eastern Region 

 iii

 

Contents 

Forward ..........................................................................................................................................................iii

Conversion Factors, Acronyms, and Abbreviations ..............................................................................vii

Summary of Procedure.................................................................................................................................1

Reporting Units and Operational Range ....................................................................................................1

Reference Materials and Documentation.................................................................................................2

Reference Material Used, Storage Requirements, and Shelf Life........................................2

Documentation ..............................................................................................................................2

Labware, Instrumentation, and Reagents .................................................................................................3

Sample Collection, Preparation, Analysis, Retention Times, and Disposal.........................................4

Sample Container, Preservation, and Handling Requirements .............................................4

Sample Preparation and Time Requirements...........................................................................5

Performing the Analysis and Time Requirements ...................................................................6

Problematic Samples....................................................................................................................7

Interferences .................................................................................................................................7

Troubleshooting and Bench Notes ............................................................................................7

Maintenance and Maintenance Records .................................................................................8

Sample Retention Time and Disposal ........................................................................................8

Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance ..........................8

Laboratory Information Management System for Light Stable Isotope (LIMS-LSI) ..........8

Quality Control (QC) Samples ......................................................................................................9

Acceptance Criteria for All QC Samples ...................................................................................9

Corrective Action Requirements ................................................................................................9

Responsible Parties for All QC/QA Functions for Procedures Covered in RSIL SOPs.......9

Data Management and Records...............................................................................................10

Health, Safety, and Waste-Disposal Information...................................................................................10

Applicable Health and Safety Issues.......................................................................................10

Personal Protection....................................................................................................10

Electrical Hazards.......................................................................................................10

Chemical Hazards .......................................................................................................10

Gas Cylinder Handling................................................................................................10

Specific Waste-Disposal Requirements .................................................................................11

Revision History ...........................................................................................................................................12

References Cited .........................................................................................................................................13

Apendixes .....................................................................................................................................................14

A. Step-by-Step Procedure to Log-In Samples to LIMS-LSI..............................................14

B. Step-by-Step Procedure to Generate an Excel Sample Workbook or to Print a 

Template and a Samples-to-Be-Analyzed List ................................................................16

C. Step-by-Step Procedure for Weighing and Storing Samples .......................................20

D. Step-by-Step Procedure of Zero Blank Autosampler Operation..................................21

E. Step-by-Step Procedure to Add Sample Information to Sequence Table..................22

F. Step-by-Step Procedure to Retrieve Data from ISODAT 2.0 for LIMS-LSI and 

for Data Back-Up ..................................................................................................................23

G. Step-by-Step Procedure to Transfer Data to LIMS-LSI, to Transfer Data to

Back-Up Computer, and to Reevaluate Old Data ............................................................24

H. Step-by-Step Procedure to Determine and Apply Correction Factors and 

Evaluate Data ........................................................................................................................25

I. Step-by-Step Procedure to Check Elemental Analyzer for Leaks................................26

J. Daily Checklist.......................................................................................................................27

K. Changing the Insertion Tube...............................................................................................28

 v 
L. Changing the Water Trap ....................................................................................................29

M. Changing the Reaction Tubes.............................................................................................30

N. Step-by-Step Procedure to Report Data...........................................................................31

Figures 

1. Diagram of the Carlo Erba Instruments NC 2500 (CE NC 2500) Elemental Analyzer ..................... 3 

2. Diagram of a Finnigan ConFlo II Open Split.......................................................................................... 4 

3. Schematic of a continuous flow isotope-ratio mass spectrometer (CF-IRMS)............................. 5 

 vi
Conversion Factors 

Multiply By To Obtain 

Length 

millimeter (mm) 0.03937 inch 

centimeter (cm) 0.3937 inch 

meter (m) 3.281 foot 

Volume 

micro liter (μL) 0.0610210

–3 cubic inch 

milliliter (mL) 0.06102 cubic inch 

cubic centimeter (cm3

) 0.06102 cubic inch

Mass 

nanogram (ng) = 10–3μg 3.527 × 10–11 ounce 

microgram (μg) = 10–3 mg 3.527 × 10–8 ounce 

milligram (mg) = 10–3 g 3.527 × 10–5 ounce 

gram (g) = 10–3 (kg) 3.527 x 10-2 ounce 

kilogram = 103

 g; 106 mg; 109μg; 1012 ng 2.205 pound 

Density 

gram per cubic centimeter (g/cm3) 0.5780 ounce per cubic inch 

Temperature

Celsius (°C) °F = 9/5 (°C) + 32 Fahrenheit (°F) 

Pressure (force/area) 

kilopascal (kPa) 9.869 × 10–3 atmosphere, standard (atm) 

kilopascal (kPa) 1.450 × 10–1 pound-force/square inch (psi) 

kilopascal (kPa) 1.000 × 10–2 bar 

kilopascal (kPa) 2.961 × 10–1 inches of mercury at 60°F 

Acronyms and Abbreviations 

ANSI American National Safety Institute 

ASR analytical services request

CF-IRMS continuous flow isotope-ratio mass spectrometer 

DIW deionized water 

EA elemental analyzer 

GC gas chromatograph 

HDPE high density polyethylene

 vii 
IAEA International Atomic Energy Agency

IRMS isotope-ratio mass spectrometer 

LIMS-LSI Laboratory Information Management System for Light Stable Isotopes 

mg/g milligram per gram

MSDS Material Safety Data Sheets 

NBS National Bureau of Standards 

NFPA National Fire Protection Association 

NWQL National Water-Quality Laboratory (USGS) 

per mill, ‰ 1/1000 

pF picofarad 

QA quality assurance 

QC quality control 

QC/QA quality control/quality assurance 

RSIL Reston Stable Isotope Laboratory

SOP standard operating procedure 

USGS U.S. Geological Survey

Symbols 

Ω ohm

< less than 

> greater than 

≥ greater than or equal 

≤ less than or equal 

 viii 
Determination of the δ(

15N/14N) of Total Nitrogen in 

Solids: RSIL Lab Code 2893 

By Kinga Révész and Haiping Qi 

Summary of Procedure 

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. An Carlo Erba NC 2500 elemental 

analyzer (EA) is used to convert total N in a solid sample into N2 gas. The EA is connected to a 

continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines relative differences 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 He atmosphere containing 

an excess of oxygen gas. Combustion products are transported by a He 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 (GC). The gas is then 

introduced into the isotope-ratio mass spectrometer (IRMS) through a Finnigan ConFlo II interface, 

which also is used to inject N2 reference gas and He for sample dilution. The IRMS is a Thermo-Finnigan 

DeltaPlus 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. 

 

Reporting Units and Operational Range 

Variations in isotope-amount ratios typically are small. Stable isotope–amount ratios commonly are 

determined as the relative difference in the ratio of the amount of the less abundant isotope (usually the 

heavy isotope) to the amount of the more abundant isotope (usually the light isotope) of a sample with 

respect to a reference. This relative difference is designated δi

E, which is a shortened form of δ(

i

E/jE) or 

δ(

i

E) and is defined according to equation 1: 

( ) ( ) ( ) ( ) ( ) ( )

n ( ) n ( )

n n n n δ = δ = δ = i j

i j i j

i i i j

E E

E E E E

E E E E

ref ref

X X − ref ref (1)

where i and j are isotopes of element E and n ( E)/n ( E) and n ( E)/n ( E) are the ratios of the isotope 

amounts in the unknown X and a reference ref

X

i

X

j

ref

i

ref

j

. A positive δiE value indicates that the unknown is more 

enriched in the amount of the heavy isotope than is the reference. A negative δi

E value indicates that the 

unknown is depleted in the amount of the heavy isotope relative to that of the reference. Values of δ iE 

have been reported in parts per hundred (% or percent), parts per thousand (‰ or per mill), and parts per 

ten thousand. For stable nitrogen isotope–amount ratios, δ15N is defined as follows: 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 1 Effective: July 29, 2003
( ) ( ) ( ) ( ) ( ) ( )

( ) N ( N)

N N N N N N N N

14

ref

15

ref

14

ref

15

ref

14

X

15

15 15 15 14 X

n n

n n n n δ = δ = δ = − (2)

The primary reference material for relative nitrogen isotope-ratio measurements (δ15N) is 

atmospheric nitrogen gas (N2), which is widespread and homogeneous and, by convention, has a 

consensus δ15N value of 0 ‰ (Mariotti, 1983). By interspersing internationally distributed isotopic 

reference materials with accepted δ values among unknown samples, the δ values can be determined on a 

normalized δ15N scale. The δ15N measurements are made with a CF-IRMS, which alternately measures 

the isotope-amount ratios of the sample N2 gas and one or more injections of the “working reference” N2

gas. Values of δ15N typically are reported in parts per thousand (‰).

The system was tested by analyzing pure inorganic samples (potassium nitrate, sodium nitrate, 

ammonium sulfate), an array of biological tissues from vertebrates and invertebrates, and geological 

samples (Révész, 1998), such as suspended organic matter in sediment. The routine analysis requires a 

minimum of 40 μg of sample as nitrogen in a maximum of 40 mg of solid sample; however, the system is 

capable of analyzing samples as small as 19 μg of N in one sample aliquot. The δ15N values of reference 

materials ranged from approximately –5 to +180 ‰, which covers much of the range of δ15N values of 

natural samples. The precision and accuracy of the results were acceptable (±0.2 ‰), and no memory

effects were observed (Qi and others, 2003). 

Reference Materials and Documentation 

Reference Material Used, Storage Requirements, and Shelf Life 

In this method, internationally distributed isotopic reference materials used when inorganic Nbearing samples are analyzed. These include IAEA-N-1 (NH4)2SO4 with δ15N of +0.43 ‰ (slightly

revised from Böhlke and Coplen, 1995; Böhlke and others, 1993), IAEA-N-2 ((NH4)2SO4) with δ15N of 

+20.41 ‰, IAEA-NO-3 (KNO3) with δ15N of +4.7 ‰, USGS25 ((NH4)2SO4) with δ15N of –30.4 ‰, 

USGS26 ((NH4)2SO4) with a δ15N of +53.7 ‰, and USGS32 (KNO3) with δ15N of +180 ‰. When organic 

nitrogen samples or mixtures of inorganic and organic nitrogen are analyzed, USGS40 and USGS41 Lglutamic acid (HO2CCH2CH2(NH2)CO2H) isotopic reference materials with δ15N of –4.52 ‰ and +47.57 

‰, respectively (Qi and others, 2003), are interspersed with samples. These two L-glutamic acids were 

prepared in the RSIL (Qi and others, 2003). Detailed preparation and calibration procedures for USGS25, 

USGS26, and USGS32 nitrate salts are given by Böhlke and others (1993). 

All of these reference materials are stored in glass bottles capped with Teflon-coated or cone-shaped 

caps to keep moisture out. Their shelf life is indefinite. 

Documentation 

All calibration results are stored in the Laboratory Information Management System for Light Stable 

Isotopes (LIMS-LSI) (Coplen, 2000) under sample identifiers N-1 (IAEA-N-1), N-2 (IAEA-N-2), N-3 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 2 Effective: July 29, 2003
(IAEA-NO-3), N-6 (USGS25), N-7 (USGS26), N-25 (USGS32), G-6740 (USGS40), and G-6741 

(USGS41). 

Labware, Instrumentation, and Reagents 

Preparatory labware and apparatus include tin capsules and a microbalance capable of measuring samples 

with 0.0001-mg precision. The analytical apparatus consists of four different units: (1) EA, (2) ConFlo 

interface, (3) IRMS, and (4) computer software. 

The EA is a Carlo Erba Instruments NC 2500 (CE NC 2500) system, and it is equipped with a 

Costech “zero blank” autosampler that holds 49 samples enclosed in tin capsules (fig. 1). Each tin capsule 

falls into the reaction-tube, which is kept at 1020 °C and is under constant He flow (90 mL/min). The 

sample immediately reacts with a measured amount of oxygen released from a 5-mL loop purged at 35 

mL/min. The reaction of oxygen with the tin capsule is exothermic, which results in localized 

temperatures of up to 1800 °C, thus ensuring complete and instantaneous sample combustion. This is 

called “dynamic flash combustion.” The combustion gases are first carried by He through an oxidative 

catalyst layer (Cr2O3) in the reaction tube, where oxidation is completed, and then through a reduction 

agent (Cu) in another reaction tube kept at 650 °C, where any nitrogen oxides are converted into 

elemental nitrogen and any excess oxygen is retained. At the outlet of the second reaction tube, the gas 

mixture (N2, usually CO2 from carbon compound in the solid, and H2O) meets a trap containing 

Anhydrone, which absorbs water. The gas mixture, now N2 and CO2, flows through a GC column

(Poraplot PQS kept at 50 °C), which separates the gases, screens out sampling noise, and ensures that 

pure nitrogen gas pass separately through the thermal conductivity detector, through the ConFlo II open 

split, and into the IRMS. 

Open to air

IRMS

(fixed)

Oxidizer

Quartz Wool (10 mm)

Quartz Wool (40 mm)

Cr2O3

Ag/Co/Co3O4

60 mm

120 mm

Figure 1. Diagram of the Carlo Erba Instruments NC 2500 (CE NC 2500) Elemental Analyzer (used with permission of 

Thermo Electron Co.). 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 3 Effective: July 29, 2003
The Finnigan ConFlo II provides the means for coupling the EA to the CF-IRMS with an open-split 

arrangement (fig. 2). The principle of an open split is that it reduces the 90 mL/min He flow needed to 

operate the EA to a 0.3 mL/min He flow needed to operate the IRMS. This is achieved by placing the end 

of the capillary that leads to the IRMS directly in the flow of He coming from the EA. The narrow 

diameter and length of this capillary limit the flow of gas into the IRMS. Furthermore, extra capillaries 

carrying reference gas or He gas can be added to the open split, thereby making it possible to inject 

reference gas into the IRMS or to dilute the sample with extra He if the sample is too large (or to direct 

gases away by dilution if they are too large to ensure total separation). 

Figure 2. Diagram of a Finnigan ConFlo II Open Split (used with permission of Thermo Electron Co.).

The IRMS is a Thermo-Finnigan DeltaPlus CF-IRMS (fig. 3). The fundamental principle of the CFIRMS technique is that a carrier gas transports the analyte through an initial stage of online chemistry for 

conversion to a form acceptable by the IRMS (Brenna and others, 1997). This is an automated system

generating online, high-precision, δ values of bulk solid and nonvolatile liquid samples. In the IRMS, gas 

molecules are ionized in a source by electrons emitted from a hot filament. The ions are accelerated into 

an analyzer, separated in a magnetic field, and collected in Faraday cup collectors. The ion-beam

intensities are measured with electrometers. This IRMS has a universal triple collector with two wide 

cups and a narrow cup in the middle, capable of measuring m/z 28, 29, and 30, simultaneously. The 

resistor–capacitor combination on the electrometer used to measure these masses are as follows: 3×108 Ω

and 680 pF on cup 1, 3 × 1010 Ω and 5 pF on cup 2, and 3 × 1011 Ω and 2 pF on cup 3. 

The Finnigan ISODAT 2.0 software is designed (1) to advance the autosampler carousel, (2) to 

control the ConFlo II interface to inject reference gases at the desired time and dilute the sample if 

desired, (3) to operate the IRMS, (4) to acquire data from the IRMS, and (5) to calculate delta values. 

Sample Collection, Preparation, Analysis, Retention Times, and 

Disposal 

Sample Container, Preservation, and Handling Requirements 

Each sample is collected in a high density polyethylene (HDPE) scintillation vial with Polyseal cap 

(Wheaton 986706), available from RSIL. Sample size should be a maximum of 1 g. The sample should be 

homogenized, oven dried (90 °C), and powdered by the submitter to 100 to 200 μm. Containers are 

labeled with isotopes whose concentrations are to be determined and with the respective laboratory code 

or schedule number. A minimum of 0.15 mg of nitrogen per sample is required. The minimum sample 

concentration is 1 mg/g sample for N. Lower concentrations can be analyzed; contact the laboratory for 

further information. No treatment, preservation, or special shipping is required. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 4 Effective: July 29, 2003
 

Figure 3. Schematic of a continuous flow isotope-ratio mass spectrometer (CF-IRMS) (modified from Clark and Fritz, 

1997). 

Sample Preparation and Time Requirements 

Sample preparation involves logging in samples to the LIMS-LSI, creating a sample work-order 

sheet, and weighing samples into capsules. 

The logging-in procedure involves logging samples in batches to LIMS-LSI that could contain from

1 to 100 samples per batch (also called a project), printing labels for each sample, and printing a summary

project report. Each sample label contains the Field ID (the identifier by which the sample submitter 

knows each sample) and the unique RSIL Lab ID assigned by the LIMS-LSI. The summary project report 

is inserted into a three-ring binder titled “Samples in Progress.” 

If samples are submitted through the USGS National Water Quality Laboratory (NWQL), the Field 

ID is a unique number for each sample assigned according to NWQL guidelines; this unique number is 

written on the analytical services request (ASR) form accompanying a sample, and the ASR information 

is entered into the LIMS-LSI system. This information is e-mailed to the submitter of the samples for 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 5 Effective: July 29, 2003
identification of any errors and subsequently e-mailed to NWQL. Copies of the ASR forms are mailed to 

NWQL. Step-by-step procedures are given in Appendix A. 

An Excel sample workbook is created. Step-by-step procedures and examples are shown in the 

Appendix B. Sample weighing includes balance conditioning, weighing appropriate sample into capsule 

(sufficient to yield 40 μg of N), closing capsules by folding them, and recording weight on template. Stepby-step procedures are shown in Appendix C. The time requirement for performing the sample 

preparation described is approximately 1 to 5 days. 

Performing the Analysis and Time Requirements 

All samples are prepared and analyzed in batches of a maximum of 80 per day, and all samples are 

analyzed in duplicate. Six aliquots of two internationally distributed isotopic reference materials with 

different δ15N values are analyzed at the beginning of a batch. Four of them are depleted in 15N, and two 

are enriched in 15N. A set of these two reference materials also is interspersed among the samples. No 

fewer than one reference material set is analyzed for every 10 unknowns. The amount of nitrogen in the 

reference materials must be in the same range as that of the samples. Therefore, one must preanalyze 

every sample to obtain the N/C concentration ratio unless it is provided by the customer. If the N/C 

concentration ratio is unknown and cannot be determined prior to isotopic analysis, a sequence of 

reference materials containing different amounts of material must be analyzed to determine a mass 

dependent correction factor. The C concentration is necessary to apply the correct dilution with He to the 

CO2 to avoid its peak interference to the N2 peak. 

The procedure involves loading the autosampler carousel with capsules containing an appropriate 

amount of sample in sequence according to the “Template” (Appendix D), loading a new sample heading 

(including sample weights) into the “Sequence Table” in ISODAT 2.0 of the IRMS software, choosing 

the appropriate “Method,” and starting sequence acquisition (Appendix E). After the analyses are 

completed, data are exported (Appendix F) to a removable disk or “memory stick” from the ISODAT 2.0 

database and transferred (Appendix G) to the LIMS-LSI system and Data Back-Up computer. Final daily

correction factors are determined by LIMS-LSI (Appendix H), based on the daily analyses of reference 

materials using equations 3 and 4 , which are presented with example numerical values: 

–4.52 ‰ = m × δ15NUSGS40 – workingrefgas + b (3) 

+47.57 ‰ = m × δ15NUSGS41 – workingrefgas + b (4) 

The values –4.52 ‰ and +47.57 ‰ are the assigned values of the two international reference materials 

(USGS40 and USGS41), respectively. The δ15Nref – workingrefgas values in the equations 3 and 4 are the mean 

daily delta values of the respective international reference materials relative to the working reference gas; 

b is the additive correction factor and m is the expansion coefficient correction factor. When two or more 

reference materials with different isotopic compositions are analyzed, the correction for sample blank 

does not need to be applied if the magnitude of the blank in the samples and reference materials is 

identical. However, if only a single reference material is analyzed, only one-point calibration is possible; 

therefore, a blank correction should be applied. 

If replicates do not agree within acceptable tolerances, they are analyzed until acceptable statistics are 

achieved. The computerized LIMS-LSI will not release data until the statistics are acceptable. The time 

requirement for performing the analyses described above is a minimum of two days. 

The systematic procedure is listed in the “Lab Procedures” binder. The supervisor reviews suggested 

changes before they are adopted. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 6 Effective: July 29, 2003
Problematic Samples 

Problematic samples include those that do not have nitrogen and carbon concentration ratios prior to 

isotopic analysis. In that case, the C/N amount ratio needs to be determined by a preliminary analysis to 

be able to determine the sample amounts that gives an appropriate amount of N (40 μg) and to be able to 

determine the amount of dilution of CO2 with He. 

Interferences 

There are no known interferences with this analytical technique. However, it should be pointed out 

that if samples contained a mixture of different nitrogen sources, reported isotope-ratio values would 

represent the isotopic composition of the total nitrogen in the sample. The δ15N values of specific N 

species cannot be provided with this analytical technique. 

Troubleshooting and Bench Notes 

The most common problems with this analytical technique are (1) incomplete combustion, 

(2) leakage in the system, particularly in the EA, and (3) insufficient linearity of the IRMS. The fact that 

the melting point of the compounds being combusted are usually higher or close to the temperature of the 

reaction tube (1020 °C) could create insufficient combustion. The “flash point” has a higher temperature, 

approximately 1800 °C (because the tin oxidation reaction is exothermic); therefore, it is critical to create 

a sharp, sudden, bright, single flash. This can be done by coordinating (1) He pressure and flow rate, 

(2) oxygen pressure and flow rate, and (3) sample “start time.” The system is so sensitive that even a 1-

second difference in the sample dropping time can make a difference in the brightness of the flash, peak 

shape, peak area, and, consequently, the δ result. The optimum set-up parameters of the RSIL EA are 

cycle = 100, oxy = 60 (O2 flow stops flowing into autosampler), sample start = 10, and sample stop = 40.

The He regulator is set for 150 kPa, and He flow setup is 95 mL/min, which actually measures 

120 mL/min at the vent. The oxygen regulator is set for 150 kPa, and the oxygen flow rate is 54 mL/min 

at purge. The oxygen loop is 5 mL. The oven temperature of the GC is 50 °C. 

Even a tiny leak can interfere with the result; it can create double peaks, an unstable analysis, and so 

forth. The high He flow rate makes the system more sensitive to leaks (Bernoulli principle). Leaks can 

cause uncontrollable changes in the flow rate, which could interfere in the quantitative combustion, in the 

peak shape, in the peak area, and consequently, in the δ value. Ash accumulation is also critical. Although 

tin oxide serves as a catalyst in the reaction, it also partially “clogs” the system, interfering with the flow 

rate, although not necessarily in a measurable manner. However, this assumes a nonrandom interference 

that causes the shift in δ value. By frequently analyzing reference materials, this shift can be corrected. 

However, after approximately 50 samples (one carousel), it is advisable to remove the ashes (Révész, 

1998). The leak-checking procedure is given in Appendix I. A leak is indicated in the IRMS when m/z 28 

and 29 are high and the ratios of m/z 28, 32, and 40 (N2, O2, and Ar) reflect atmospheric compositions. 

Acceptable levels for m/z 28 and 29 are approximately 0.15 and 0.015 V, respectively, with typical IRMS 

settings. (See “Daily Checklist” in Appendix J.) 

The IRMS must be focused carefully. The analyst should start with the original factory setting. In the 

RSIL, the settings (in priority order) are as follows: Extraction = 7.00; X focusing = 4.8; Voltage = 8.00; 

Trap = 5.7; Electron = 7.8; Y1 focusing = 3.00; Y2 focusing = 3.8; X deflection = 6.4; Extraction = 5.6;

and X-focusing symmetry = 3. Emission current is critical. The higher it is, the higher the signal is but the 

poorer the linearity is. The IRMS is temperature sensitive; therefore, it must be operated in a temperaturecontrolled environment with all of the side panels on. The resistor–capacitor combinations on the 

electrometers are as follows: 3 × 108 Ω and 680 pF for cup 1, 3 × 1010 Ω and 5 pF for cup 2, and 3 × 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 7 Effective: July 29, 2003
1011 Ω and 2 pF for cup 3. The instrument is capable of measuring m/z 28 and 29, and m/z 30 = NO 

=14N16O primarily, which is a sign of contamination or incomplete reduction. 

An internal precision check needs to be conducted using the “Zero Enrichment” method (standard gas 

on/off 10 times), and it must give a standard deviation of ± 0.1 ‰ or better. The “Ratio Linearity” test 

must give 0.12 ‰/V or better linearity. An external precision check needs to be performed as needed, 

approximately every week or so; samples of the same amount need to be analyzed within ± 0.010 mg. The 

1–σ standard deviation must be ± 0.2 ‰ or better for n = 10. If either of these criteria has not been met, 

the IRMS cannot be used and must be refocused. 

Maintenance and Maintenance Records 

Routine maintenance is necessary for the upkeep of the IRMS vacuum system, including

(1) checking the pump performance from time to time, (2) changing the pump oil, and (3) changing the 

oil cartridge in each turbomolecular pump at 6-month intervals. Pump conditions, including date of oil 

changes, problems, and repairs to the pump, are listed in the pump database (file path: LIMS 

C:\RSIL\vacuum pumps). Maintenance of the EA includes (1) changing the insertion tube every day 

(Appendix K), (2) changing the water trap approximately every 500 samples (Appendix L), (3) changing 

reaction tubes approximately every 200 to 250 analyses (Appendix M), and (4) cleaning the sample 

carousel every week. The IRMS also requires a daily check (Appendix J). A logbook is kept for each 

IRMS, where notes of maintenance checks, history of normal settings, problems, and repairs are listed. 

Maintenance of ISODAT 2.0 includes importing (transferring) results from the ISODAT 2.0 database 

to the LIMS-LSI computer hard disk and the Data Back-Up computer hard disk (Appendix G). 

Sample Retention Time and Disposal 

Samples are retained in the RSIL for at least 4 months after reporting data. Samples are then 

discarded unless the submitter has requested that the samples be returned. 

The ISODAT sample files from the IRMS computer are kept indefinitely on two different hard disks 

of the Data Back-Up computer. Paper reports are kept for a few weeks. Analytical results from the IRMS 

are transmitted to LIMS-LSI and kept indefinitely. No data are entered by hand, and no manual 

calculations are performed on the data. 

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

Assurance 

Laboratory Information Management System for Light Stable Isotope (LIMS-LSI) 

In the RSIL, the LIMS-LSI (Coplen, 2000) is used for data acquisition, processing, and evaluation. 

This system is a database program capable of (1) storing information about samples, (2) storing the results 

of mass spectrometric delta values of samples after importing from the ISODAT database, (3) calculating 

analytical results using standardized algorithms stored in a database, (4) normalizing delta values using 

isotopic reference materials, and (5) generating templates for convenient sample placement to facilitate 

loading of automated IRMS sample-preparation manifolds. With this system, the following can be 

achieved: (1) quality assurance (QA), (2) laboratory efficiency, (3) reduction of workload and errors 

owing to the elimination of retyping of data by laboratory personnel, and (4) a decrease of errors in data 

reported to sample submitters. This database provides a complete record of information on how 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 8 Effective: July 29, 2003
laboratory reference materials have been analyzed and provides a record of what correction factors have 

been used. It provides an audit trail for the RSIL. 

Quality Control (QC) Samples 

Samples are prepared and analyzed in batches—a maximum of 80 daily. Each batch contains 

approximately six reference materials at the beginning, four depleted in 15N and two enriched in 15N, and 

later in the batch one depleted in 15N for every ten samples. The last analysis of a batch is that of a 

reference material depleted in 15N. All of these reference materials serve as QC samples. The preparation 

and analytical cost of these isotopic reference materials is the responsibility of RSIL. Both RSIL and 

NWQL monitor these results. Quarterly, RSIL prepares a summery of results of these internationally

distributed isotopic reference materials and make them available to NWQL. 

Daily, the analyst (1) examines the computer printouts for indications of analytical problems, 

(2) determines the daily additive and expansion correction factors by the LIMS-LSI, and (3) applies 

corrections factors to isotopic data. The values of these corrections factors, along with the date and range 

of analysis numbers, are recorded manually in the laboratory “EABook” even though the data are already

in the LIMS-LSI. After printing the list of isotopic results from the “Table of Samples in Progress,” the 

analyst reviews the results and determines which samples need to be analyzed a third time to achieve 

acceptable results (i.e., ∆δ ≤ 0.2 ‰). 

Acceptance Criteria for All QC Samples 

Acceptance criteria for QC samples are the same as acceptance criteria for the other samples. The 

rules are as follows: 

• If standard deviation is ≤ 0.2 ‰, use mean delta. 

• If there are three or more analyses, delete the outlier and recalculate. 

• If standard deviation of this recalculation is ≤ 0.2 ‰, use mean from this recalculation. 

• If none of the above is the case, the result is not accepted, and corrective action is required. 

Corrective Action Requirements 

If the analyst finds any problem with the daily reference-sample data, the analyst contacts the 

supervisor. The trouble-shooting process will require an evaluation and reanalysis of certain samples to 

ascertain the origin of the problem. 

If samples do not give satisfactory results after three or more separate analyses, the analyst averages 

all the data and reports the mean value. Such analytical results are indicated with a comment, and the 

customer will be advised by e-mail or other means. If the sample was submitted through the NWQL, it is 

the responsibility of the customer to determine whether the data need to be qualified. If so, the NWQL 

will mark the result in USGS databases appropriately. 

Responsible Parties for All QC/QA Functions for Procedures Covered in RSIL SOPs 

The analyst, with supervisory approval, is responsible for qualifying data and notifying customers. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 9 Effective: July 29, 2003
Data Management and Records 

In addition to evaluating daily sample analyses, every week an analyst evaluates the data project by

project, reports results to the customers, and files final project data reports in the laboratory

“Correspondence” binder (Appendix N). 

Health, Safety, and Waste-Disposal Information 

Applicable Health and Safety Issues 

Personal Protection 

Safety glasses and protective gloves are recommended whenever samples are handled, especially

when the samples are of biological origin. For other precautions and safety procedures, consult Material 

Safety Data Sheets (MSDSs), which are on file in the laboratory, and 

http://www.ilpi.com/msds/#Manufacturers provides links to MSDSs of most chemical companies. 

Electrical Hazards 

Electrical systems must conform to the National Electric Code, National Fire Protection Association 

Code (NFPA 70-1971), and the American National Standards Institute (ANSI) Code (C1-1971). Consult

the U.S. Geological Survey’s Safety and Environmental Health Handbook (U.S. Geological Survey, 

2002). 

Shock hazards exist inside the instruments. Only an authorized service representative or an individual 

with training in electronic repair must remove panels or circuit boards where voltages are greater than 

20 V. The instruments require a third-wire protective grounding conductor. Three-to-two wire adapters 

are unsafe for these instruments. 

Chemical Hazards 

The hazardous chemicals used in the process are Cr2O3 and Co3O4, which are used in the oxidation 

reaction tube. Sometimes the reaction tube cracks, and the packing material leaks out. When this happens, 

protective gloves and a full-face mask are required during the cleanup process. All the materials, 

including gloves and any cleaning towels, need to be collected in a plastic bag and disposed of as 

hazardous waste. All samples must be carefully inspected upon receipt for obvious indications of hazards. 

Gas Cylinder Handling 

Compressed gas cylinders must be handled and stored according to the Safety and Environmental 

Health Handbook (U.S. Geological Survey, 2002). Each cylinder must be (1) carefully inspected when 

received; (2) securely fastened at all times with an approved chain assembly or belt; (3) capped at all 

times when not in use; (4) capped when transported; (5) transported only by a properly designed vehicle 

(hand truck); and (6) stored separately with other full, empty, flammable, or oxidizing tanks of gas, as 

appropriate. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 10 Effective: July 29, 2003
Specific Waste-Disposal Requirements 

Used reaction tubes containing Cr2O3 and CO3O4 must be collected in a closed container and must be 

given to the safety, health, and environment officer for disposal. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 11 Effective: July 29, 2003
Revision History 

Publication Series and Series Number: Techniques and Methods 10-C11 (Book 10, Section C, Chapter 11) 

Publication Title: Determination of the δ(

15N/14N) of Total Nitrogen in Solids: RSIL Lab Code 2893 

Publication Authorship: Révész, Kinga, and Qi, Haiping 

First Version and Date of First Release: December 2006 

Current Version and Date of Current Release: July 2007 

Summary of Product Components 

Component Description 

Last Revised 

In Publication Version 

Date of 

Last Revision 

List of Revisions (latest version first): 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 12 Effective: July 29, 2003
References Cited 

Böhlke, J. K., and Coplen, T. B., 1995, Interlaboratory comparison of reference materials for nitrogenisotope-ratio measurements, in Reference and intercomparison materials for stable isotopes of light 

elements: Vienna, Austria, International Atomic Energy Agency, IAEA-TECDOC-825, p. 51–66. 

Böhlke, J. K., Gwinn, C. J. and Coplen, T. B., 1993, New reference materials for nitrogen-isotope-ratio 

measurements: Geostandards Newsletter, v. 17, p. 159–164. 

Brenna, J. T., Corso, T. N., Tobias, H. J., and Caimi, R. J., 1997, High-precision continuous-flow isotoperatio mass spectrometry: Mass Spectrometry Reviews, v. 16, p. 227–258. 

Clark, I., and Fritz, P., 1997, Environmental Isotopes in Hydrogeology: Lewis Publishers, 328 p. 

Coplen, T. B., 2000, A guide for the laboratory information management system (LIMS) for light stable 

isotopes—Version 7 and 8: U. S. Geological Survey Open-File Report 00-345, 121 p. 

Mariotti, A., 1983, Atmospheric nitrogen is a reliable standard for natural 15N abundance measurements: 

Nature, v. 303, p. 685-687. 

Qi, H. P., Coplen, T. B., Geilmann, H., Brand, W. A. and Böhlke, J. K., 2003: Two new organic reference 

materials for δ13C and δ15N measurements and a new value for the δ13C of NBS 22 oil: Rapid 

Communications in Mass Spectrometry, v. 17, p. 2483–2487. 

Révész, K., 1998, Carbon and Nitrogen isotope ratios of organic and inorganic bulk samples: Instrument 

performance and Intercalibration: The 5th Canadian Continuous-Flow Isotope-ratio Mass Spectrometry

Workshop, Ottawa Ontario, August 16–19, 1998. 

U.S. Geological Survey, 2002, USGS Handbook 445-3-H, Safety and Environmental Health Handbook,

435 p. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 13 Effective: July 29, 2003
Appendix A. Step-by-Step Procedure to Log-In Samples to LIMS-LSI 

1. For samples submitted through NWQL: 

a. Match up information on sample bottles with information on ASR forms by spreading out ASR 

forms and placing each bottle on its respective ASR form. Check for broken bottles. 

b. Assign NWQL #s based on the Julian date of the Monday following the submission date. Check 

note on bulletin board for “Next NWQL #.” Write NWQL #s on ASR forms, then update “Next 

NWQL #” on bulletin board. 

c. Use “New Project Log-In” in LIMS-LSI to assign N-#s; field IDs are the Station IDs. Submission 

date is the date samples are logged in. 

d. Enter all ASR information into LIMS-LSI, sample by sample. 

e. Print out two Project Reports, Labels (two for each sample), and Sample Range forms. 

f. Put a label on a sample bottle and on the corresponding ASR form; crosscheck Field IDs between 

bottles and ASR forms. 

g. Make one photocopy of each ASR form. 

h. Enter G-# range into the appropriate template. 

i. Proofread information on Sample Range forms against ASR forms (recruit help if necessary). 

Make corrections in LIMS-LSI, if necessary and print out corrected Sample Range Forms. Initial 

and date both Project Reports to indicate that proofreading is complete. 

j. In LIMS-LSI, save NWQL Headings to a diskette. 

k. In ISOTOPES e-mail on the common-use PC, copy headings into new message from diskette by

opening headings-file in Notepad and copying/pasting to new message. Print copy of headings 

and e-mail to each project chief for information review and NWQL [Attn: Jeanne Hatcher 

(jhatcher@usgs.gov)].

l. Mail copies (not originals) of ASR forms and corrected Sample Range forms to NWQL [National 

Water Quality Laboratory, Attn: Jeanne Hatcher, U.S. Geological Survey, P.O. Pax 25708, MS

407, Building 95, Denver Federal Center, Denver, CO 80225-0608 (Tel: 303-236-3481)].

Envelope should be mailed every Friday.

m. Punch holes in original ASRs and put in “Central Lab” binder along with project reports and date 

on piece of tape. Punch holes in NWQL headings and other project report and place in “Samplesin-Progress” binder. 

n. Add samples to the “Table of Samples to Be Analyzed” in LIMS-LSI. 

i. Click the “Projects” button of LIMS-LSI. 

ii. Select the project that was logged in. 

iii. Click the “Templates” button. 

iv. Select “EA for N.” 

v. Click “Add” and close LIMS-LSI. 

o. Put samples in cabinets for storage until analyzed. 

2. For samples submitted directly to RSIL:

a. For sample submitter: 

i. Download “RSIL Excel Worksheet” from RSIL website at http://isotopes.usgs.gov/. 

ii. Fill out the requested sample information. 

iii. Send diskette and a hard copy along with the samples. 

b. For RSIL personnel: 

i. Match up information on sample bottles with submitted “Excel Worksheet.” 

ii. Enter all Excel Worksheet information into LIMS-LSI by loading the diskette. Submission 

date is the date samples are logged in. 

iii. Use “New Project Log-In” in LIMS-LSI to assign G-#s; field IDs are the Station IDs. 

iv. Print out one Project Reports and container labels (one for each sample). 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 14 Effective: July 29, 2003
v. Put a label on a sample bottle and crosscheck Field ID’s between bottles and Excel 

Worksheet forms. 

vi. Enter G-# range into the appropriate template. 

vii. Punch holes in original Excel Worksheet and all the information for the project and put in 

“Samples-in-Progress” binder. 

viii. Add samples to the “Table of Samples to Be Analyzed” in LIMS-LSI. 

1. Click the “Projects” button of LIMS-LSI. 

2. Select the project that was logged in. 

3. Click the “Templates” button. 

4. Select “EA for N.” 

5. Click “Add” and close LIMS-LSI. 

ix. Put samples in cabinets for storage until analyzed. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 15 Effective: July 29, 2003
Appendix B. Step-by-Step Procedure to Generate an Excel Sample 

Workbook or to Print a Template and a Samples-to-Be-Analyzed List 

Excel Sample Workbook 

1. Use default worksheet-weighing template and add samples to be analyzed. 

2. Fill the appropriate amount in the cells of the rows labeled “Set weight mg.” 

3. Print first worksheet in workbook. 

4. Write the tray ID and the date on both the diskette and paper template. 

5. Put them near the balance. 

Template 

1. Use “Print Template” in LIMS-LSI. 

2. Select “appropriate template” for EA and the “Delta Plus” IRMS. 

3. Select “New Template” (dialog box informs you how many samples are waiting to be analyzed). 

4. Click “OK.” 

5. Click “Print.” 

6. Insert diskette to receive sample headings. 

7. Click “OK.” 

8. Write the day of the week that these samples should be analyzed on both the diskette and paper 

template. 

9. Put them near the balance. 

10. Exit LIMS-LSI.

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 16 Effective: July 29, 2003
Worksheet 1. Weighing template.

[International reference materials are in bold font.]

1 2 3 4 5 6 7 8 9 10 11 12

Our Lab ID G-6740 G-6740 G-6740 G-6740 G-6741 G-6741 G-9031 G-9031 G-9032 G-9032 G-9033 G-9033

A Set weight mg 0.75 0.75 0.75 0.75 0.75 0.75 0.8 0.8 0.8 0.8 0.8 0.8

Actual weight,

mg 

0.75 0.69 0.73 0.766 0.751 0.764 0.804 0.798 0.799 0.802 0.805 0.803

Comment USGS40 USGS40 USGS40 USGS40 USGS41 USGS41

Our Lab ID G-9034 G-9034 G-9035 G-9035 G-6741 G-6741 G-9036 G-9037 G-9037 G-9038 G-9036 G-9039

B Set weight mg 0.8 0.8 0.8 0.8 0.75 0.8 0.8 0.8 0.8 0.8 0.8 0.8

Actual weight,

mg 

0.801 0.802 0.795 0.803 0.759 0.795 0.801 0.799 0.793 0.804 0.801 0.795

Comment USGS40 USGS41

Our Lab ID G-9039 G-9040 G-9040 G-6740 G-6741 G-9041 G-9042 G-9042 G-9043 G-9043 G-9044 G-9044

C Set weight mg 0.8 0.8 0.8 0.75 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8

Actual weight,

mg 

0.804 0.804 0.795 0.766 0.797 0.802 0.8 0.805 0.804 0.797 0.804 0.801

Comment USGS40 USGS41

Our Lab ID G-9045 G-9045 G-6740 G-6741 G-9046 G-9047 G-9047 G-9048 G-9048 G-9049 G-9049 G-9050

D Set weight mg 0.8 0.8 0.75 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8

Actual weight,

mg 

0.795 0.803 0.766 0.799 0.798 0.796 0.803 0.805 0.805 0.797 0.802 0.796

Comment USGS40 USGS41

Our Lab ID G-9051 G-6740 G-6741 G-9052 G-9052 G-9053 G-9053 G-9054 G-9054 G-9055 G-6740 G-6741 

E Set weight mg 0.8 0.75 0.8 1.7 1.7 1.4 1.4 1.1 1.1 0.74 0.74 0.75

Actual weight,

mg 

0796 0.756 0.795 1.703 1.705 1.405 1.399 1.102 1.097 0.739 0.737 0.795

Comment USGS40 USGS41 USGS40 USGS41

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 17 Effective: July 29, 2003
Worksheet 2. Samples to be analyzed.

[International reference materials are in bold font]

Line Identifier Port Comment Amount Amt Unit

1 G-6740 A1 USGS40 0.75 mg

2 G-6740 A2 USGS40 0.769 mg

3 G-6740 A3 USGS40 0.763 mg

4 G-6740 A4 USGS40 0.766 mg

5 G-6741 A5 USGS41 0.751 mg

6 G-6741 A6 USGS41 0.764 mg

7 G-9031 A7 0.804 mg

8 G-9031 A8 0.798 mg

9 G-9032 A9 0.799 mg

10 G-9032 A10 0.802 mg

11 G-9033 A11 0.805 mg

12 G-9033 A12 0.803 mg

13 G-9034 B1 0.801 mg

14 G-9034 B2 0.802 mg

15 G-9035 B3 0.795 mg

16 G-9035 B4 0.803 mg

17 G-6740 B5 USGS40 0.757 mg

18 G-6741 B6 USGS41 0.795 mg

19 G-9036 B7 0.801 mg

20 G-9037 B8 0.799 mg

21 G-9037 B9 0.793 mg

22 G-9038 B10 0.804 mg

23 G-9038 B11 0.801 mg

24 G-9039 B12 0.795 mg

25 G-9039 C1 0.804 mg

26 G-9040 C2 0.804 mg

27 G-9040 C3 0.795 mg

28 G-6740 C4 USGS40 0.766 mg

29 G-6741 C5 USGS40 0.797 mg

30 G-9041 C6 0.802 mg

31 G-9042 C7 0.8 mg

32 G-9042 C8 0.805 mg

33 G-9043 C9 0.804 mg

34 G-9043 C10 0.797 mg

35 G-9044 C11 0.804 mg

36 G-9044 C12 0.801 mg

37 G-9045 D1 0.795 mg

38 G-9045 D2 0.803 mg

39 G-6740 D3 USGS40 0.766 mg

40 G-6741 D4 USGS41 0.799 mg

41 G-9046 D5 0.798 mg

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 18 Effective: July 29, 2003
Line Identifier Port Comment Amount Amt Unit

42 G-9047 D6 0.796 mg

43 G-9047 D7 0.803 mg

44 G-9048 D8 0.805 mg

45 G-9048 D9 0.805 mg

46 G-9049 D10 0.797 mg

47 G-9049 D11 0.802 mg

48 G-9050 D12 0.796 mg

49 G-9051 E1 0.796 mg

50 G-6740 E2 USGS40 0.756 mg

51 G-6741 E3 USGS41 0.795 mg

52 G-9052 E4 1.703 mg

53 G-9052 E5 1.705 mg

54 G-9053 E6 1.405 mg

55 G-9053 E7 1.399 mg

56 G-9054 E8 1.102 mg

57 G-9054 E9 1.097 mg

58 G-9055 E10 0.739 mg

59 G-6740 E11 USGS40 0.737 mg

60 G-6741 E12 USGS41 0.761 mg

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 19 Effective: July 29, 2003
Appendix C. Step-by-Step Procedure for Weighing and Storing Samples 

1. Samples should be homogenized and dried. 

2. Insert Template diskette in the computer connected to the microbalance. 

3. Condition balance (this step should be done once a day): 

a. Place empty capsule on balance and close door. Wait for reading to stabilize (the “mg” on the 

display appears). Tare the balance. 

b. Remove and replace capsule and make sure the stabilized weight is 0.000 mg. 

c. Repeat these steps until the balance is stable. 

4. Remove capsule from balance, add sample and weigh the filled capsule. Repeat until you have the 

desired weight (which gives 0.15 μg of N). 

5. Enter sample weight on the template. 

6. Fold cup; secure sample in it. 

7. Repeat steps 4 to 6 for every sample. 

8. Note: 

a. Do not cross-contaminate samples. 

b. Make sure the spatula and sample area are cleaned using Kimwipes between each sample. 

c. Always allow balance to stabilize before removing capsule. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 20 Effective: July 29, 2003
Appendix D. Step-by-Step Procedure of Zero Blank Autosampler 

Operation

1. Before opening the lid, make sure the isolation valve (between sample chamber and reaction tube) is 

closed (arrow towards you) and make sure the He purge isolation valve (on the left) is closed. 

2. Open the purge vent on the top of the autosampler to vent the sample chamber.

3. Release the three fittings holding the lid close and open the lid. 

4. Place your samples and close the lid. Load 49 samples for a 50-position carousel, leave the first hole 

empty. 

5. Secure the lid with three bolts. Start all three bolts, and then lightly tighten two at a time, moving 

around the lid until they are all completely tight. 

6. Open the He purge isolation valve (screw down), purge the sample chamber for 5 min at He flow rate 

of 298 mL/min. Make sure the purge vent valve (on top) is open. Press your finger on top of the vent 

valve for 2 s, then release; you should hear the sound of a pressure release. 

7. Close the He purge vent valve (screw down), wait for 2 min for gas pressure at sample chamber and 

He flow rate to stabilize. Close He purge isolation valve. 

8. Open isolation valve (arrow toward up).Wait for 2 min for stabilized baseline. Normally when the 

emission current set at 0.54 mA/0.48 mA, with He carrier flow rate of 90 mL/min, one should see m/z 

28 on cup 1 at approximately 10 mV, m/z 29 on cup 2 at approximately 8 mV to 12 mV, and m/z 30 

on cup 3 at approximately 140 mV (Appendix J). 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 21 Effective: July 29, 2003
Appendix E. Step-by-Step Procedure to Add Sample Information to 

Sequence Table 

1. Insert diskette with “Weighing Template” on it. 

2. Open “Sequence File” under “EA configuration.” 

3. Open “Weighing Template” in Excel. 

4. “Copy” and “Paste” the list of Sample ID, sample weight from template to sequence table. 

5. Select appropriate “method” for each sample. 

6. Define reference line and blank line. 

7. Start. 

8. Give Folder Name: Comment 

a. Select pre: “Date.” 

9. Give File Name: 

a. Select pre: “Analyzes #.” 

b. Select post: “Identifier 1.” 

c. Select: “Print Result.” 

10. Click OK. 

11. Wait for first sample to be analyzed. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 22 Effective: July 29, 2003
Appendix F. Step-by-Step Procedure to Retrieve Data from ISODAT 2.0 

for LIMS-LSI and for Data Back-Up 

1. For LIMS-LSI: 

a. Select “Result” in ISODAT 2.0. 

b. Select the result folder you wish to export data from.

c. Select all the individual analyses you want to retrieve by right clicking the selected file. 

d. Select “Reprocess.” 

e. Give a file name. 

f. Add export template previously designed.

g. Open. 

h. Click OK. (Reprocessing takes 1–2 min.) 

i. Open Excel. 

j. Find the file you reprocessed (E-drive, Finnigan, ISODAT 2.0, Global, User, CONFLO II, 

Interface, Result: File name). 

k. Open it in Excel. 

l. Save as: “A” drive. Keep in Lotus format. 

m. Define all reference peaks by adding #1 under column “Is Ref.?.” 

n. Now the file can be imported to LIMS-LSI. 

2. For Data Back-Up Computer: 

a. Go to Windows explorer in ISODAT 2.0 computer. 

b. Find the drive where the data are (D). 

c. Choose: “Finnigan.” 

d. Choose: “User.” 

e. Choose the inlet system where you have data (Gas Bench or EA). 

f. Choose “Result folder.” 

g. Transfer data to Zip disk or “memory stick.” 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 23 Effective: July 29, 2003
Appendix G. Step-by-Step Procedure to Transfer Data to LIMS-LSI, to 

Transfer Data to Back-Up Computer, and to Reevaluate Old Data

1. Transfer data to LIMS-LSI: 

a. Start LIMS. 

b. Choose “Import Analysis.”

c. Choose IRMS “Delta Plus.” 

d. Click “Import.” 

e. Select the file that will be imported. 

f. Select columns containing δ15N data. Check the boxes to import these two columns. 

g. Click Import. Note: Sample ID, sample weight, Peak Area, Analyses #s are automatically

imported to LIMS-LSI. 

2. Transfer data to Data Back Up computer: 

a. Go to Windows Explorer in the Data Back-Up computer. 

b. Find the drive your back ups are stored. 

c. Choose: “RSIL.” 

d. Choose: “Mass. Spec. Analysis Back Up.” 

e. Choose: “P.” (Stands for DeltaPlus IRMS). 

f. Under that folder create a new folder. The name of the folder should be the date range when those 

analyses were done that you want to back up. 

g. Transfer data to that folder. 

h. Make back ups every 2 weeks or so, as required. 

3. Reevaluate old data: 

a. Find your samples in the Data Back-Up computer. 

b. Transfer data by a Zip disk or “memory stick” to the computer where a virtual version of 

ISODAT 2.0 is installed. 

c. Reevaluate your data. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 24 Effective: July 29, 2003
Appendix H. Step-by-Step Procedure to Determine and Apply Correction 

Factors and Evaluate Data 

1. Open “Correction Factors and Normalization Equations” in LIMS-LSI. 

2. Select the IRMS and isotope, such as “P (Delta Plus) for 15N.” 

3. Select “Query.” 

4. Double click on the last sample analyzed on that day.

5. Evaluate data of the reference materials. 

6. Choose “Normalize with all References.” 

7. Accept “Expansion Correction and Additive Correction factors.” 

8. Print out correction factor sheet. 

9. Report daily reference values and correction factors along with date and range of analysis number to 

the “EA” binder. 

10. Go back to LIMS-LSI main menu by closing open windows. 

11. Choose “Print Samples in Progress,” 

a. Open “Sample in Progress.” 

b. Choose appropriate isotope. 

c. Choose appropriate prefix (W for water, N for nitrogen, S for sulfur, G for gas or general). 

d. Put in sample ID range from “Samples-to-Be-Analyzed” sheet. Click Print. 

12. Review results; determine repeats. 

13. Put repeats back to Table of Samples to Be Analyzed. 

a. Go back to LIMS-LSI main menu. 

b. Open “Print Templates.” 

c. Select appropriate template name for the IRMS with which the samples are analyzed. 

d. Find the sample in the “List of samples.” 

e. Change “Repeats” from 0 to 1. 

f. Close Windows and exit LIMS-LSI. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 25 Effective: July 29, 2003
Appendix I. Step-by-Step Procedure to Check Elemental Analyzer for 

Leaks 

1. Close the VENT carrier output using the proper cap (provided). 

2. Adjust the He pressure to 150 kPa (regulator is on the front central panel), wait 3 min to equilibrate 

gas in the system. 

3. Close He inlet valve by turning the above regulator counter clockwise. 

4. If the gauge needle does not move, there is no leak. 

5. If the gauge needle moves, indicating the lost of pressure, there is a leak in the system. The 

decreasing pressure rate accounts for the degree of leakage. 

6. Locate the leak by separating and testing the system segment by segment, using the He detector. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 26 Effective: July 29, 2003
Appendix J. Daily Checklist 

Analyst in charge: ______________________Date: ______________________

Weekly: 

1. Change working reference gas tank and He gas tank if the pressure is < 500 psi. Order new ones for a 

spare; reference gas is SO2 ANHY by Matheson, He carrier is zero grade, O2 is research grade.

2. Change water and CO2 trap after approximately 200 samples, or when it is necessary. 

3. Check and clean autosampler carousel. 

4. Change the reaction tube after approximately 600 samples, or when it is necessary. 

THESE ITEMS ARE TO BE CHECKED OFF AS YOU CHECK THEM DAILY! 

1. Check He, O2, and reference gas flow. [ ] 

2. Check EA reaction-tube temperature (1020 °C) 

3. Change insertion tube (ash-collector liner) in the reaction tube. [ ]

4. Check background masses. [ ]

Typical background at N2/CO2 configuration 

At emission current: 0.54 mA/0.48 mA 

Cups Mass Intensity (V) Mass Intensity (V) Resistor (Ω) Capacity (pF) 

1 28 0.010 0 3 × 108 680 

2 29 0.007 18 1.256 3 × 1010 5 

3 30 0.140 18 6.818 3 × 1011 2 

5. Perform Ref on/off method three times to stabilize IRMS. [ ]

6. Check peak center. If it is off default value by more than 50, do mass calibration. [ ]

7. Analyze Ref on/off method 10 times to stabilize IRMS (standard deviation should be better than 

±0.1 ‰). [ ]

Optimal ConFlo Pressure Setting N2 

(bar) 

N2 signal (V) Mass 29 on Cup 2 

0.25 0.173

0.50 0.450

0.75 0.773

1.00 1.180

1.25 1.560

1.50 Optimal setting 2.074 

1.75 2.634

2.00 3.199

8. Check paper in printer. [ ]

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 27 Effective: July 29, 2003
Appendix K. Changing the Insertion Tube 

The insertion tube needs to be changed before a template is run. 

1. Manually close needle valve near the ion source. 

2. On the menu of the Model 2500 EC under “Spc. Fun.,” choose “Std By” and press “enter.” The O2

and He should be turned off. 

3. Unscrew the metal seals under the sample carousel to access the reaction tube. 

4. Using the heat protective glove and the wire tool, remove the insertion tube from the reaction tube 

and place in the metal can. Be aware that the tube will be very hot! 

5. Insert clean tube that has 0.5 cm of quartz wool packed at the bottom, and tap it down with the wire 

tool. 

6. Replace the carousel and tighten the metal seals with a wrench. 

7. Turn the O2 and He back on by pressing “enter” and return the screen to the temperature readout by 

pressing “Spc. Fun.” 

8. Open the needle valve. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 28 Effective: July 29, 2003
Appendix L. Changing the Water Trap 

Change the water trap after every 200 samples. 

1. Retrieve quartz turnings, quartz wool, magnesium perchlorate, and a clean water trap from Delta

Plus

supplies. 

2. Under a hood, pack one end of the clean water trap with 1 cm of quartz wool. 

3. On a piece of wax paper, create a mix of approximately 70 % magnesium perchlorate and 30 % 

quartz turnings, pack the mix into the water trap tube, leaving 1 cm of empty space. 

4. Pack the open end of the water trap with quartz wool. 

5. Unscrew the red plastic ends from the used water trap and replace it with the clean water trap; be sure 

to replace the rubber O-rings on the ends of the clean water trap and tighten the red ends. 

6. Insert the plug into the vent and watch for any drop in pressure to check for a leak in the system. 

After 5 min, if everything looks acceptable, replace the vent line. 

7. Under the “Spc. Fun.” menu of the model 2500 EA, choose “CNT” (counter) and zero “D,” to set 

back the water-trap counter. 

8. Clean the water trap by pushing all the mixture out of the tube into the trash can and use a clean 

cotton swab to wipe out the inside of the tube. Rinse the tube with DIW, and dry it in the oven. 

Return this tube to the water trap bag in the drawer. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 29 Effective: July 29, 2003
Appendix M. Changing the Reaction Tubes 

The reaction tubes should be changed approximately every 500 to 600 samples. [The new reaction tubes 

will need to equilibrate over night before they can provide accurate results; thus, change the reaction 

tubes at the end of the day.]

1. Manually close the needle valve near the ion source. 

2. Turn the Model 2500 EA to “Std By” with both gases off. 

3. Lower the oxidation tube temperature to less than 900 °C; leave the reduction tube temperature as it 

is. 

4. Retrieve the reaction tubes from the cabinet. 

5. Insert the insertion tube into the top of the oxidation tube; there will already be a plastic tube in the 

reaction tube that should be removed. 

6. Place black O-rings on the top of the reaction tubes. Make sure that all O-ring connections are clean 

and free of any dust. 

7. Loosen the top metal seal and remove the bottom metal seal. Go back and completely remove the top 

seal. It will be very hot! Use oven gloves! 

8. Remove quartz reaction tubes and place them metal can, place clean reaction tubes in column. Make 

sure the O-rings are clean; then replace the top. 

9. On the bottom, put on the metal pieces with metal O-rings first and then add the clean rubber O-rings. 

Raise the bottom portion and screw together. Then, tighten the connections with wrenches, and put 

the metal supports back in place. 

10. Turn the gases back on; then, go to “CNT” in the menu under “Spc. Fun.” Set to zero the counter of 

the oxidation reaction tube, “B,” as well as that of the reduction reaction tube “C.”

11. Insert the plug into the vent and close the He supply. Watch for any decrease in the pressure to check 

for a leak in the system. If everything looks okay after 3 min, open the He supply and replace the vent 

line. 

12. Open the needle valve. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 30 Effective: July 29, 2003
Appendix N. Step-by-Step Procedure to Report Data 

1. Open “Store Samples in Progress” in LIMS-LSI. 

2. Choose the appropriate isotope. 

3. Choose sample ID range from “Sample in Progress” print out. 

4. Store data. 

5. Go back to the LIMS-LSI main menu. 

6. Open “Project” and find the appropriate project in the list. 

7. Select “Print Report” and check whether the project report contains all the results. If not, search for 

the missing results in the database. 

8. Select “Results,” transfer data in Excel format or (and) text format to a diskette, and report data to 

customer through e-mail. 

9. Click “Print Report” to print a project report and put it in the “Correspondence” binder along with all 

other documents in the “Samples In Progress” binder that are related to this project. 

10. If the samples were submitted through the NWQL, click “NWQL Export” and transfer data in NWQL 

format to a disc; report these data to the NWQL by e-mail. Print a copy of the NWQL export file and 

save in the “Correspondence” binder with the project report printed in the step above. 

Prepared by: Kinga Révész and Haiping Qi RSIL SOP: 2893 

Approved by: T. B. Coplen Page 31 Effective: July 29, 2003