δ

15N and Non-Carbonate δ13C Values for Two 

Petroleum Source Rock Reference 

Materials and a Marine Sediment Reference 

Material 

Kristin O. Dennen1, Craig A. Johnson2, Marshall L. Otter3, Steven R. Silva4, and Gregory A. Wandless5

1

Eastern Energy Resources Team, U.S. Geological Survey, Reston, Virginia 

2

USGS Crustal Imaging and Characterization Team Stable Isotope Laboratory, Geology Discipline, 

Denver, Colorado 

3

Stable Isotope Laboratory, The Ecosystems Center, Marine Biological Laboratory, Woods Hole, 

Massachusetts 

4

USGS Menlo Park Stable Isotope and Tritium Labs, Water Resources Discipline, Menlo Park, California 

5

USGS Reston Stable Isotope Laboratory, Geology Discipline, Reston, Virginia 

Open-File Report 2006-1071 

U.S. Department of the Interior 

U.S. Geological Survey 

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and 

stratigraphic nomenclature. Any use of trade, firm, or product names is for descriptive purposes only and does not 

imply endorsement by the U.S. Government 
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Gale A. Norton, Secretary 

U.S. Geological Survey 

P. Patrick Leahy, Acting Director 

U.S. Geological Survey, Reston, Virginia 2006 

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Suggested citation: Dennen, K. O., Johnson, C.A., Otter, M.A., Silva, S. R., Wandless, G.A, .2006, δ

15N and Non-carbonate δ13C 

Values for Two Petroleum Source Rock Reference Materials and a Marine Sediment Reference Material: U. S. Geological Survey 

Open File Report 2006-1071. 

Any use of trade, product, or firm names 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. 
 

Contents 

Abstract................................................................................................................................................. 1 

Introduction .......................................................................................................................................... 2 

Methods ................................................................................................................................................ 2 

Terminology ...................................................................................................................................... 2 

Sample Preparation......................................................................................................................... 2 

Results ................................................................................................................................................... 3 

Statistical Analysis of Results ....................................................................................................... 3 

Discussion ............................................................................................................................................ 4 

Conclusions .......................................................................................................................................... 5 

References ........................................................................................................................................... 6 

Acknowledgements ............................................................................................................................ 7 

Alphabetical list of contributing laboratories.................................................................................7 

List of Figures 

1. Histograms and descriptive statistics for carbon analyses. 

2. Histograms and descriptive statistics for nitrogen analyses. 

3. Kolomogorov-Smirnov Comparison Cumulative Fraction Plots. 

List of Tables 

1. Reference materials used for isotopic and elemental calibrations. 

2. Analytical results for individual laboratories. 

3. Descriptive statistics. 

4. Test for normality of data distribution for analyses from laboratories A and B. 

5. Suggested isotopic and elemental values. 
 

 δ15N and Non-carbonate δ13C Values for 

Two Petroleum Source Rock Reference 

Materials and a Marine Sediment Reference 

Material 

Kristin O. Dennen1, Craig A. Johnson2, Marshall L. Otter3, Steven R. Silva4, and Gregory A. Wandless5

1

Eastern Energy Resources Team, U.S. Geological Survey, Reston, Virginia 

2

USGS Crustal Imaging and Characterization Team Stable Isotope Laboratory, Geology Discipline, 

Denver, Colorado 

3

Stable Isotope Laboratory, The Ecosystems Center, Marine Biological Laboratory, Woods Hole, 

Massachusetts 

4

USGS Menlo Park Stable Isotope and Tritium Labs, Water Resources Discipline, Menlo Park, California 

5

USGS Reston Stable Isotope Laboratory, Geology Discipline, Reston, Virginia 

Abstract 

δ

13C and δ15N values have been determined for SDO-1, (Devonian Ohio Shale) 

and SGR-1 (Eocene Green River Shale), petroleum source rock reference materials and 

PACS-2, a modern marine sediment reference material. Analyses were performed after 

acid fumigation so that the data refer to non-carbonate carbon (δ

13Cncc and Wt % Cncc). 

Acid fumigation had no apparent effect on nitrogen isotopic analyses. The results are 

averages of determinations from four analytical laboratories and are as follows: 

Identification δ

13C (‰) Wt% Cncc δ15N (‰) Wt% N

SDO-1 -30.0 + 0.1 9.64 + 0.19 - 0.8 + 0.3 0.36 + 0.01 

SGR-1 -29.3 + 0.1 24.01 + 0.38 17.4 + 0.4 0.81 + 0.02 

PACS-2 -23.3 + 0.2 3.17 + 0.06 4.9 + 0.1 0.27 + 0.01 

Data are reported as Mean + the 95% confidence interval. Νitrogen isotope data are 

reported relative to atmospheric nitrogen. Carbon isotope data are reported relative to 

Vienna Peedee Belemnite (VPDB). 

1
 

Introduction 

Samples of United States Geological Survey (USGS) Certified Reference 

Materials USGS Devonian Ohio Shale (SDO-1), and USGS Eocene Green River Shale 

(SGR-1), and National Research Council Canada (NRCC) Certified Marine Sediment 

Reference Material (PACS-2), were sent for analysis to four separate analytical 

laboratories as blind controls for organic rich sedimentary rock samples being analyzed 

from the Red Dog mine area in Alaska. The samples were analyzed for stable isotopes of 

carbon (δ

13Cncc) and nitrogen (δ15N), percent non-carbonate carbon (Wt % Cncc) and 

percent nitrogen (Wt % N). 

SDO-1, collected from the Huron Member of the Ohio Shale, near Morehead, 

Kentucky (Kane and others, 1990), and SGR-1, collected from the Mahogany zone of the 

Green River Formation (Gladney and Roelandts, 1987) are petroleum source rocks used 

as reference materials for chemical analyses of sedimentary rocks. PACS-2 is modern 

marine sediment collected from the Esquimalt, British Columbia harbor (NRCC Institute 

for National Measurement Reference materials, 2000). 

The results presented in this study are, with the exceptions noted below, the first 

published for these reference materials. There are published information values for the 

elemental concentrations of “organic” carbon (Wt % Corg measured range is 8.98 - 10.4)

and nitrogen (Wt % Ntot 0.347 with SD 0.043) only for SDO-1. (Kane and others, 1990) 

The suggested values presented here should be considered “information values” as 

defined by the NRCC Institute for National Measurement Reference materials (2000) and 

should be useful for the analysis of 13C, 15N, C and N in organic material in sedimentary 

rocks. 

Methods 

Terminology 

Isotope ratio measurements are calculated by the formula: 

δ (in ‰) = (Rx / Rs

 - 1) x1000 

where R denotes the ratio of the heavy to light isotope (e.g., 15N/14N), and Rx

 and Rs are the 

ratios in the sample and standard, respectively. Nitrogen isotope data are reported relative 

to atmospheric nitrogen. Carbon isotope data are reported relative to Vienna Peedee 

Belemnite (VPDB). 

 The term “non-carbonate carbon” (Cncc), referring to carbon isotopic (δ

13Cncc) and 

elemental values (Wt. % Cncc) determined on acid fumigated samples, is used in this paper 

because acid fumigation is assumed to remove carbonate carbon. Any carbon remaining 

in the sedimentary organic matter or samples after acid fumigation is assumed to be “noncarbonate”, that is, reduced forms of carbon, including graphite. 

Sample Preparation 

The laboratories participating in this study are designated Lab A, Lab B, Lab C, 

and Lab D. (An alphabetical list of the laboratories is provided after the 

2
 

Acknowledgments section. However the letter designation does not correspond to a 

laboratory’s position on the list.) Each laboratory analyzed the samples according to their 

own protocols. Information on reference materials used for calibration is shown in Table 

1, according to the recommendations of Coplen (1996). 

The author followed the acid fumigation procedure of Harris and others (2001) to 

prepare the samples at the USGS in Reston, Virginia. Before weighing, the samples were 

dried overnight in an oven at 60° C, stored in a desiccator and allowed to cool to room 

temperature. All samples for any particular reference material came from the same bottle, 

which was thoroughly mixed before each weighing. Samples were weighed on a microbalance not to exceed 20 μmoles organic carbon in silver foil cups. While three of the 

four laboratories determined all analyses on one sample, Lab D requested separate 

samples for nitrogen and carbon analysis. These samples were weighed to provide 

5 μmoles of nitrogen in tin foil cups and did not undergo HCl fumigation. 

The samples (with the exception noted above) were fumigated with hydrochloric 

acid (HCl) to remove carbonate carbon. Numbered plastic trays holding the silver foil 

cups of weighed samples were seated in glass chambers with approximately 100 ml of 

concentrated (12.1 N) HCl contained in beakers at the bottom. The chambers were sealed 

and samples were exposed to the acid fumes for 48 hours. After fumigation, the sample 

trays were removed and dried overnight at 60° C. The foil cups were then sealed and 

crushed to a spherical shape for analysis. 

The author also prepared working calibration reference materials at the USGS in 

Reston, Virginia, from International Reference Materials (IRM) USGS40 and USGS41 

(Qi and others, 2003), for Lab A and Lab B. Samples of 600 - 750 μg were weighed on a 

micro-balance into silver foil cups and fumigated as described above. The laboratories 

were provided with reference material volumes and calculated estimates of elemental 

carbon and nitrogen content. 

Results 

Analytical results from the four laboratories are shown in Table 2. The data were 

combined and spreadsheet functions were used to describe basic statistics and determine 

confidence intervals. The distributions of δ

13Cncc, δ15N, Wt % Cncc, Wt. % N are shown as 

histograms with descriptive statistics in Figures 1 and 2. Lab D’s contributions to the 

combined data sets for δ

15N and Wt. % N are labeled on Figure 2 in order to determine 

the effect of acid fumigation on nitrogen values. Descriptive statistics for the combined 

data are summarized in Table 4. Suggested values are shown in Table 5. 

Statistical Analysis of Results 

Differences in laboratory analytical procedures can be a problem in comparing 

light stable isotope ratio measurements from several laboratories (Coplen and others, 

1983). In an attempt to identify any source of variability in the results among the 

laboratories, the distributions of the results were analyzed statistically. Lab A and Lab B 

used the same calibration reference materials, IRM USGS40 and IRM USGS41 (See 

Table 1) prepared in the same way, as described above. Also, results from Lab A and Lab 

3
 

B had enough numbers (>10) for statistical tests (Lab C and D received and reported on 

only one set of duplicate samples), so these two sets of analyses were considered good 

candidates for statistical examination and comparison. The results for a test for normality 

of the distributions are shown in Table 3. 

Because most of the data sets were not normally distributed, the KolmogorovSmirnoff (K-S) test was chosen to compare the sets of data from Lab A and Lab B. This 

test determines whether or not two sets of data belong to the same population. (Davis, 

1973) It requires neither large numbers of data nor normally distributed data, but it also 

gives no information about the sources of variation among and between data sets 

(compared to analysis of variance techniques which require large numbers of values and 

normal distributions). The College of St. Benedict/St. John’s University, Minnesota online calculator was used to do calculations for the tests 1. The results are shown in Figure 

3. 

Discussion 

Except for the δ

13C values for SDO-1 in the K-S comparison test between Labs A 

and B (See Figure 3), the results from the two laboratories are considered to be 

statistically different. Lab A’s sets of values are normally distributed except for δ

15N 

(Table 3). Lab A did not report δ

15N values for SDO-1 and SGR-1, nor did they report 

enough Wt % N values for a statistical test for these two materials. The fact that Lab A’s 

reported δ 15N values are not normally distributed and that there are no reported δ

15N 

values for two of the reference materials or enough Wt% N values for these reference 

materials for a statistical analysis indicates bias in the analysis for isotopic and elemental 

nitrogen from Lab A. According to Lab A, the amount of nitrogen in the aliquots of 

SDO-1 and SGR-1 was too small to give reliable δ

15N values. This could easily account 

for the bias in the analysis for δ

15N, but it does not account for the differences in the 

carbon values between Lab A and Lab B. 

None of Lab B’s sets of analyses are normally distributed except for δ 15N. (Table 

3) During the year in which the samples were analyzed, Lab B replaced the detector on 

their mass spectrometer with one much more sensitive to carbon. This may be a factor in 

the biased distribution of Lab B’s analyses for carbon and can account for some of the 

differences between the two laboratories’ carbon analyses. 

Lab A randomized the order in which the samples were run. Lab B ran triplicate 

samples one after the other, with standard reference materials inserted after every five 

unknowns. The difference in sample order protocol would require different drift 

correction procedures. Some of the variation is probably due to differences in correction 

procedures for drift and blanks like those described for nitrogen by Böhlke and Coplen 

(1995). 

Another factor in the range of values, illustrated in Figures 1 and 2, and Table 2, 

could be sample inhomogeneity. SGR-1, SDO-1 and PACS-2 are all complex, naturally 

occurring materials with varying ranges of elemental carbon and nitrogen. They are not 

 

1 http://www.physics.csbsju.edu/stats/KS-test.n.plot_form.html (accessed 3/22/2006)

4
 

as homogeneous as chemically simple, synthetic reference materials, constructed to have 

ideal analytical ranges for several analytes. Maximum sample volume for isotopic 

analysis is limited by the size of the entrance into the combustion chamber of the 

analytical instrument. Getting a representative sample of heterogeneous material in the 

limited volume required can be very difficult. This can be remedied in part, by analyzing 

multiple samples, which has the effect of broadening the range of values, and narrowing 

the confidence limits. 

Analyzing separately for carbon and nitrogen eliminates difficulties encountered 

when there are large differences in the concentrations of carbon and nitrogen in one 

sample. Sample volumes can be calculated and weighed specifically for either carbon or 

nitrogen and the calibration range can be simplified. 

According to Harris and others (2001), fumigating sedimentary organic material 

in acid can change the nitrogen isotopic value, but not significantly. Because samples for 

both Lab A and Lab B were fumigated, fumigation can not explain the difference in these 

sets of data. Lab D analyzed δ

15N and elemental nitrogen separately from carbon on 

samples that were not acid fumigated. There is no discernable pattern in the placement of 

Lab D’s contributions on the histograms for δ15N and elemental nitrogen (Figure 2), 

which implies that bias in acid fumigation had no effect on δ

15N and Wt. %N 

determinations for SDO-1, SGR-1 and PACS-2. 

The confidence intervals for the δ

13C values reported in Table 5 are close to the 

range of those reported in other interlaboratory comparisons, for example, in Stichler 

(1995) where the 95% confidence intervals for δ

13C range from 0.025 to 0.150. The 95 % 

confidence intervals for δ

15N reported here are similar to the range (0.186 to 0.473) for 

reference materials in Gonfiantini and others (1995). The elemental values for SDO-1 

compare favorably to the published information values for nitrogen and “organic” carbon. 

Conclusions 

This report establishes SDO-1, (Devonian Ohio Shale) and SGR-1 (Eocene Green 

River Shale), petroleum source rock reference materials and PACS-2, a modern marine 

sediment reference material as a set of reference materials useful for analysis of 13C, 15N, 

C and N in organic material in sedimentary rocks. 

Acid fumigation of samples to remove carbonate carbon affected neither δ

15N 

values nor Wt. %N for these reference materials. Thus although some change in δ

15N 

values has been shown for soil samples, such shifts are not characteristic of all rock 

types. 

Stichler and others (1995) recommend adopting and documenting common data 

reduction procedures to increase the precision of interlaboratory comparison of materials. 

Obtaining formal certified values for these and other geologic reference materials will 

require standardization of analytical protocols, analytical blank determinations and data 

reduction procedures among participating laboratories. This should probably include 

separate analysis for carbon and nitrogen isotopes and elemental concentrations. 

5
 

References 

Böhlke, J.K., and Coplen, T.B., 1995, Interlaboratory comparison of reference materials for 

nitrogen-isotope-ratio measurements, in Reference and intercomparison materials 

for stable isotopes of light elements: Vienna, International Atomic Energy Agency, 

IAEA-TECDOC-825, p. 51-66. 

Coplen, T. B., 1996. Editorial: More uncertainty than necessary: Paleoceanography, v. 11, 

no. 4, p. 369-370. 

Coplen, T. B., Kendall, C., and Hopple, J., 1983, Comparison of stable isotope reference 

samples, Nature 302, p. 236 - 238 

Davis, J.C., 1973. Statistics and Data Analysis in Geology, John C. Wiley and Sons, New 

York, p. 273. 

Harris, D., Horwath, W. R., and van Kessel, C., 2001. Acid fumigation of soils to remove 

carbonates prior to total organic carbon or carbon-13 isotopic analysis: Soil 

Science Society of America Journal, v. 65, p. 1853-1856. 

Kane, J.S., Arbogast, B.F., and Leventhal, J.S. 1990, Characterization of Devonian Ohio 

Shale as a USGS geochemical reference sample: Geostandards Newsletter, v. 14, 

p. 169-196 

Gladney, E. S. and Roelandts, I. 1987 Compilation of elemental concentrations for USGS 

BHVO-1, MAG-1, QLO-1, RGM-1, SCo-1, SDC-1, SGR-1, and STM-1, Geostandards 

Newsletter, v. 12, p 253- 362. 

Gonfiantini, R., Stichler, W., and Rozanski, K., 1995, Reference materials and 

Intercomparison Materials Distributed by the International Atomic Energy Agency 

for Stable Isotope Measurements in, Reference and intercomparison materials for 

stable isotopes of light elements: Vienna, International Atomic Energy Agency, 

IAEA-TECDOC-825, p. 13-29. 

National Research Council of Canada Institute for National Measurement Reference 

materials, 2000, Certified Reference Material Data Sheet for PACS-2, Marine 

Sediment Reference Material for Trace Elements and Other Constituents including 

Butyltins. http://inms-ienm.nrc-cnrc.gc.ca/en/calserv/crm_files_e/HISS-1_MESS3_PACS_2_certificate.pdf (accessed 3/23/06) 

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

reference materials for δ

13C and δ15N measurements and a new value for the δ13C of 

NBS 22 oil: Rapid Communications in Mass Spectrometry, v. 17, Issue 22, p. 2483-

2487. 

Stichler, W., 1995, Interlaboratory Comparison of New Materials for Carbon and Oxygen 

Isotope Ratio Measurements in Reference and intercomparison materials for 

stable isotopes of light elements: Vienna, International Atomic Energy Agency, 

IAEA-TECDOC-825, p. 67-74. 

6
 

Acknowledgements 

Haiping Qi of the USGS Reston Stable Isotope Laboratory provided samples of 

the new International Reference Materials USGS40 and USGS41 and as a reviewer, 

greatly improved the manuscript with her suggestions. Reviewer Steve Wilson of the 

USGS Central Mineral Resources Team also provided helpful comments. Tyler Coplen 

of the USGS Reston Stable Isotope Laboratory provided guidance on isotopic procedures 

and reporting guidelines. Lawrence Drew of the USGS Eastern Mineral Resources Team 

made sure that the use of statistical tests was appropriate. 

Alphabetical list of contributing laboratories 

Stable Isotope Laboratory, The Ecosystems Center, Marine Biological Laboratory, 

Woods Hole, Massachusetts, http://ecosystems.mbl.edu/silab 

USGS Crustal Imaging and Characterization Team Stable Isotope Laboratory, Geology 

Discipline, Denver, Colorado 

USGS Menlo Park Stable Isotope and Tritium Labs, Water Resources Discipline, Menlo 

Park, California 

USGS Reston Stable Isotope Laboratory, Geology Discipline, Reston, Virginia. 

http://isotopes.usgs.gov 

7
Number of Values

δ

13Cncc

 Wt. % 

C ncc

‰

Number of Values Number of Values

PACS-2

Mean -30.0

SD 0.4

P value 0.03

Sample size 29

Mean -29.3

SD 0.3

P value 0.01

Sample size 27

Mean -23.3

SD 0.6

P value 0.01

Sample size 42

Mean 24.0

SD 1

P value *0.97

Sample size 27

Mean 9.64

SD 0.53

P value 0.01

Sample size 30

Mean 3.17

SD 0.22

P value 0.00

Sample size 44

Figure 1. Histograms and descriptive statistics for carbon isotopic and elemental results 

of combined data sets. The 95% confidence interval about the mean is shown in 

shaded bars. *P value is large enough to consider the distribution to be normal. SD is 

standard deviation. Sample size is the number of results used to calculate the mean.

SGR-1

SDO-1

-31.0 -30.5 -30.0 -29.5 -29.0 -28.5

0

1

2

3

4

5

6

7

-30.0 -29.8 -29.6 -29.4 -29.2 -29.0 -28.8 -28.6 -28.4 -28.2

0

1

2

3

4

5

6

7

-26.0 -25.5 -25.0 -24.5 -24.0 -23.5 -23.0 -22.5 -22.0

0

2

4

6

8

10

8.5 9.0 9.5 10.0 10.5 11.0 11.5

0

1

2

3

4

5

6

7

21 22 23 24 25 26 27

0

1

2

3

4

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2

0

1

2

3

4

5

6
-2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2

0

1

2

3

4

5

6

15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 4.5 5.0 5.5 6.0 6.5 7.0

0

1

2

3

4

5

6

0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42

0

1

2

3

4

5

6

7

0.70 0.72 0.74 0.76 0.78 0.80 0.82 0.84 0.86 0.88 0.90

0

1

2

3

4

5

0.22 0.24 0.26 0.28 0.30 0.32

0

2

4

6

8

10

12

14

16

18

δ

15N 

Number of Values Number of Values Number of Values

‰ Wt. % 

SDO-1

SGR-1

PACS-2

N 

Mean -0.84

SD 0.53

P value 0.08

Sample size 17

Mean 0.36

SD 0.03

P value 0.11

Sample size 26

Mean 17.4

SD 0.9

P value 0.47*

Sample size 18

Mean 0.81

SD 0.05

P value 0.85*

Sample size 23

Mean 4.91

SD 0.46

P value 0.14

Sample size 36

Mean 0.27

SD 0.02

P value 0.00

Sample size 36

Figure 2. Histograms and descriptive statistics of combined data sets for nitrogen 

analyses. The 95% confidence interval about the mean is shown in shaded bars. *P 

value is large enough to consider the distribution to be normal. SD is standard deviation. Sample size is the number of analyses used to calculate the mean. The positions of 

Lab D’s results are labelled and the lack of a pattern of Lab D’s results within the group 

suggests that acid fumigation had no effect on nitrogen isotopic and elemental analyses. (Lab D analyzed duplicate samples.)

D D

D

D

D

D

D

D
–30.6 –30.4 –30.2 –30.0 –29.8 –29.6

1.0

.8

.6

.4

.2

0

KS–Test Comparison Cumulative Fraction Plot

X

Cumulative Fraction

9.0 9.5 10.0 10.5

1.0

.8

.6

.4

.2

0

KS–Test Comparison Cumulative Fraction Plot

X

Cumulative Fraction

–25.5 –25.0 –24.5 –24.0 –23.5 –23.0 –22.5

1.0

.8

.6

.4

.2

0

KS–Test Comparison Cumulative Fraction Plot

X

Cumulative Fraction

2.8 3.0 3.2 3.4 3.6

1.0

.8

.6

.4

.2

0

KS–Test Comparison Cumulative Fraction Plot

X

Cumulative Fraction

4.5 5.0 5.5 6.0 6.5

1.0

.8

.6

.4

.2

0

KS–Test Comparison Cumulative Fraction Plot

X

Cumulative Fraction

.23 .24 .25 .26 .27 .28 .29

1.0

.8

.6

.4

.2

0

KS–Test Comparison Cumulative Fraction Plot

X

Cumulative Fraction

δ13Cncc SDO-1 Wt. % Cncc SDO-1

δ13Cncc PACS-2 Wt % Cncc PACS-2

δ15N PACS-2

Isotopic Value

Wt % N PACS-2

Concentration

Lab A

Lab B

Lab A

Lab B

Lab B

Lab B

Lab B

Lab B

Lab A

Lab A

Lab A Lab A

Figure 3. Kolmogorov-Smirnov (K-S) Comparison Cumulative Fraction Plots. Steps are data 

points on the X axis. The Y axis represents the cumulative fraction of the data smaller than the 

data point. The K-S test compares the difference between the plots (D value) and computes a P 

value for the probability of the analytical results being from different populations. To say the 

results are from different populations with 95% confidence, the P value must be < 0.05. *In this 

case, the P value is too large to assume the results are from different populations. Therefore they 

are considered to be similar.

D = 0.4487

P = 0.12*

D = 0.6944

P = 0.01

D = 0.6000

P = 0.01

D = 0.6154

P = 0.01

D = 0.4500

P = 0.02

D = 1.0000

P = 0
Table 1. Reference materials used for isotopic and elemental calibrations

Lab A Lab B Lab C Lab D 

Working Reference Materials used for Isotopic Analysis (values are those used by the laboratories) 

USGS40: δ13C -26.24 ‰ δ15N - 4.52 ‰ 

USGS41: δ13C +37.76 ‰ 

δ15N +47.57 ‰ 

(Qi and others, 2003). 

USGS40: δ13C -26.24 ‰ 

δ15N - 4.52 ‰ 

USGS41: δ13C +37.76 ‰ 

δ15N +47.57 ‰ 

(Qi and others, 2003). 

EDTA: δ13C -32.24 ‰ 

δ15N +0.72 ‰ 

In-house working reference 

Reference Materials used for calibrating Working Reference Materials (values are those used by the laboratori

Same as above Same as above δ13C: 

NBS 18 carbonatite -5.0 ‰ NBS 19 limestone +1.95 ‰ NBS 22 oil -29.7 ‰ IAEA CH 6 sucrose -10.4 ‰ δ15N: IAEA N1 ammonium sulfate +0.4 ‰ IAEA N2 ammonium sulfate +20.3 ‰ USGS 25 ammonium  sulfate -30.2 ‰ (provisional) USGS 26 ammonium sulfate +53.6 ‰ (provisional) 

δ13C: 

NBS 21 graphite -28.1 ‰ δ15N: 

IAEA N1 ammonium sulfate +0.4 ‰ IAEA N2 ammonium sulfate +20.3 ‰ 

Working Reference Materials for Elemental Concentrations 

Atropine USGS40 

USGS41 

EDTA In-house working reference 

EDTA-Ethylenediamenetetraaceticacid NBS-National Institute of Standards and Technology (NIST) Reference Material 

Most of the Standard Reference Materials listed here are distributed by NIST on behalf of the International Atomic Energy Agency (IA

Descriptions of the materials may be found at: https://srmors.nist.gov/tables/104-10.htm (accessed 3/22/2006). 
Lab A Lab B Lab C Lab D Lab A Lab B Lab C Lab D Lab A Lab B Lab C Lab D Lab A Lab B Lab C Lab D

SDO-1 -30.40 -30.14 -28.83 -29.7 8.83 9.92 11.33 9.48 -1.51 -0.31 -1.0 0.30 0.39 0.37 0.37

-30.00 -30.27 -29.03 -29.8 8.84 9.86 9.83 9.52 -1.8 -0.38 -0.7 0.30 0.39 0.35 0.37

-29.90 -30.12 9.64 9.61 -0.74 0.38 0.36

-29.80 -30.16 9.96 9.5 -0.58 0.36 0.36

-30.00 -30.17 9.18 9.56 -0.67 0.34 0.36

-30.00 -30.22 8.99 9.57 -0.62 0.34 0.36

-30.10 -30.22 9.45 9.78 -0.67 0.32 0.37

-30.00 -30.21 9.29 9.82 -0.47 0.31 0.37

-30.00 -30.16 10.61 9.43 -0.61 0.35 0.37

-30.60 -30.12 9.65 9.52 -0.44 0.36

-30.70 -29.60 9.32 9.55 -0.31 0.37

-30.50 -29.75 9.32 10.85 -1.90 0.41

-30.40 9.17 9.87 -1.6 0.39

SGR-1 -29.50 -29.31 -28.43 -29.2 23.05 25.36 25.74 25.10 15.56 16.92 18.3 0.71 0.88 0.78 0.87

-29.40 -29.28 -28.51 -29.6 22.14 23.75 25.65 24.42 15.98 17.13 18.4 0.75 0.87 0.78 0.88

-29.30 -29.37 23.51 23.09 18.39 0.79 0.79

-29.60 -29.28 23.85 22.98 17.90 0.72 0.79

-29.50 -29.31 25.93 23.54 17.82 0.81 0.81

-29.80 -29.34 24.16 22.10 18.02 0.76

-29.80 -29.30 24.15 24.00 17.51 0.82

-29.40 -29.48 22.67 24.69 17.40 0.85

-29.80 -29.36 24.56 24.46 18.48 0.82

-29.36 23.43 17.80 0.82

-29.32 23.47 17.51 0.83

-29.35 23.94 18.20 0.84

-29.12 24.44 16.08 0.87

-29.12 24.16 16.00 0.87

PACS-2 -23.00 -24.72 -23.11 -23.4 2.83 3.43 3.20 3.29 4.70 4.70 4.75 4.2 0.23 0.28 0.28 0.30

-22.90 -25.51 -24.46 -23.3 2.80 3.67 4.06 3.09 4.80 4.68 5.62 4.5 0.23 0.28 0.30 0.29

-23.10 -23.61 3.01 3.21 6.50 5.49 0.24 0.28

-22.80 -23.72 2.85 3.25 4.40 5.31 0.23 0.28

-22.60 -23.70 3.06 3.25 4.40 5.16 0.26 0.28

-22.80 -23.73 3.08 3.26 4.50 5.28 0.26 0.28

-22.60 -23.83 2.98 3.28 4.40 5.10 0.26 0.28

-22.80 -23.63 2.94 3.26 4.50 5.13 0.23 0.29

-22.70 -23.72 2.93 3.18 4.70 5.36 0.23 0.28

-22.80 -23.76 2.89 3.29 5.30 4.92 0.23 0.29

-22.90 -23.69 3.25 3.28 4.70 5.16 0.26 0.28

-23.10 -23.11 3.41 3.23 4.30 5.26 0.25 0.29

-23.40 -23.12 3.15 3.18 5.16 0.29

-23.60 -23.10 3.15 3.02 5.21 0.28

-23.00 -23.13 3.07 3.11 4.95 0.28

-23.50 -23.51 3.23 3.04 4.74 0.28

-23.30 -23.18 3.34 3.07 4.87 0.28

-22.90 -23.05 3.13 3.37 4.77 0.29

-22.80 3.12 3.1 4.46 0.28

-23.10 3.21 3.09 4.76 0.28

No 

values 

reported

No 

values 

reported

Table 2. Analytical results for individual laboratories

δ13Cncc Wt% Cncc δ15N Wt% N
Table 3. Test for nomality of data distribution 

for analyses from laboratories A and B 

SDO-1 Data Set Mean SD P value 

δ

13C ‰ Lab A -30.2 0.3 0.32 

δ

13C ‰ Lab B -30.1 0.2 *0.01 

 

Wt % Cncc Lab A 9.40 0.49 0.44 

Wt % Cncc Lab B 9.76 0.37 *0.03 

 

PACS-2 

δ

13C ‰ Lab A -23.0 0.3 0.40 

δ

13C ‰ Lab B -23.7 0.6 *0.03 

 

Wt % Cncc Lab A 3.07 0.17 0.99 

Wt % Cncc Lab B 3.23 0.15 *0.01 

 

δ

15N ‰ Lab A 4.77 0.61 *0.02 

δ

15N ‰ Lab B 5.02 0.28 0.66 

 

Wt % N Lab A 0.24 0.01 0.14 

Wt % N Lab B 0.28 0.00 *0 

SD is the standard deviation. The P value is the probability 

of wrongly rejecting the hypothesis that the data from each 

lab is normally distributed. To reject the hypothesis that the 

data sets are normally distributed with a 95% probability of 

being correct, the P value must be < 0.05. *These data sets 

are not normally distributed.
Table 4. Descriptive statistics 

Identification δ

13C (‰) Wt% Cncc δ15N (‰) Wt% N 

As Reported 

SDO-1 -30.0 (0.4) 

(n=29) 

9.64 (0.53) 

(n=30) 

-0.8 (0.6) 

(n=18) 

0.36 (0.03) 

(n=26) 

SGR-1 -29.3 (0.3) 

(n=27) 

24.01 (1.01) 

(n=27) 

17.4 (0.9) 

(n=18) 

0.81 (0.05) 

(n=23) 

PACS-2 -23.3 (0.6) 

(n=42) 

3.17 (0.22) 

(n=44) 

4.9 (0.5) 

(n=36) 

0.27 (0.02) 

(n=36) 

Data are reported as Mean (Standard Deviation) 

(n = number of values used to calculate the mean) 

Carbon isotope data are reported relative to Vienna Peedee Belemnite (VPDB). 

Nitrogen isotope data are reported relative to atmospheric nitrogen. 

Table 5. Suggested isotopic and elemental values 

Identification δ

13C (‰) Wt% Cncc δ15N (‰) Wt% N

SDO-1 -30.0 + 0.1 9.64 + 0.19 - 0.8 + 0.3 0.36 + 0.01 

SGR-1 -29.3 + 0.1 24.01 + 0.38 17.4 + 0.4 0.81 + 0.02 

PACS-2 -23.3 + 0.2 3.17 + 0.06 4.9 + 0.1 0.27 + 0.01 

Data are reported as Mean + the 95% confidence interval. 

Carbon isotope data are reported relative to Vienna Peedee Belemnite (VPDB). 

Nitrogen isotope data are reported relative to atmospheric nitrogen.