NISTIR 6849 

Description and Results of the 2000 NIST/NOAA Interlaboratory 

Comparison Exercise Program for Organic Contaminants and 

Trace Elements in Marine Mammal Tissues 

John R. Kucklick 

Steven J. Christopher 

Paul R. Becker 

Rebecca S. Pugh 

Barbara J. Porter 

Michele M. Schantz 

Elizabeth A. Mackey 

Stephen A. Wise 

Teresa K. Rowles 

 
NISTIR 6849 

Description and Results of the 2000 NIST/NOAA Interlaboratory 

Comparison Exercise Program for Organic Contaminants and 

Trace Elements in Marine Mammal Tissues 

John R. Kucklick 

Steven J. Christopher 

Paul R. Becker 

Rebecca S. Pugh 

Chemical Science and Technology Laboratory 

Analytical Chemistry Division 

Charleston Laboratory 

Barbara J. Porter 

Michele M. Schantz 

Elizabeth A. Mackey 

Stephen A. Wise 

Chemical Science and Technology Laboratory 

Analytical Chemistry Division 

Teresa K. Rowles 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

July 2002

U.S. Department of Commerce 

Donald L. Evans, Secretary 

National Institute of Standards and Technology 

Arden Bement, Director
i

TABLE OF CONTENTS 

LIST OF APPENDICES .............................................................................................................. ii

LIST OF TABLES .......................................................................................................................iii

LIST OF FIGURES ...................................................................................................................... v

DISCLAIMER.............................................................................................................................. vi

ABSTRACT................................................................................................................................. vii

INTRODUCTION......................................................................................................................... 1

Background on Interlaboratory Comparison Exercises and Associated Quality 

Assurance Activities Conducted by NIST for the MMHSRP................................................ 2

Preparation, Analysis, and Distribution of Control Materials ................................................................ 2

Development of Standard Reference Materials (SRMs)......................................................................... 3

Interlaboratory Comparison Exercises .............................................................................................. 5

PART 1: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR ORGANIC 

CONTAMINANTS IN MARINE MAMMAL TISSUES.......................................................... 8

Materials Used in the Exercise ................................................................................................. 8

Exercise Requirements and Target Analytes.......................................................................... 9

Evaluation of the Exercise Results......................................................................................... 11

Establishment of Consensus Values................................................................................................. 11

Reported Results ......................................................................................................................... 11

Assignment of z-and p-scores......................................................................................................... 13

Results and Discussion ............................................................................................................ 17

Conclusions .............................................................................................................................. 18

PART 2: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR TRACE 

ELEMENTS IN MARINE MAMMAL TISSUES................................................................... 19

Materials Used in the Exercise ............................................................................................... 19

Exercise Requirements and Target Analytes........................................................................ 19

Evaluation of the Exercise Results......................................................................................... 19

Establishment of Consensus Values................................................................................................. 19

Assignment of z-and p-scores......................................................................................................... 20

Normalization Factors ................................................................................................................. 21

Results and Discussion ............................................................................................................ 22

z- and p-scores ........................................................................................................................... 23

Normalization Procedures ............................................................................................................ 23

Youden Diagrams........................................................................................................................ 24

Methylmercury Data .................................................................................................................... 24

Conclusions .............................................................................................................................. 24

LITERATURE CITED .............................................................................................................. 25
ii

LIST OF APPENDICES 

PART 1: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR 

ORGANIC CONTAMINANTS IN MARINE MAMMAL TISSUES .............................................A-E 

A. Tabular Results by Analyte from Individual Laboratories ....................................................A-1-26 

B. Graphical Results of PCB Congener and Lipid Data Reported by All 

Laboratories ...........................................................................................................................B-1-30 

C. Graphical Results of Organochlorine Pesticide Data Reported by All 

Laboratories ...........................................................................................................................C-1-19 

D. Additional Analyte Data Reported by Individual Laboratories.............................................D-1-6 

E. Tabular Summary of Methods Used for Analysis by Each Laboratory.................................E-1-8 

PART 2: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR TRACE 

ELEMENTS IN MARINE MAMMAL TISSUES...........................................................................F-L 

F. List of Participants for the Trace Elements Exercise.............................................................F-1 

G. Raw Laboratory Results and Summary Statistics..................................................................G-1-7 

H. Consensus Results and Summary Statistics...........................................................................H-1 

I. Consensus Mean Plots for Various Elements in Beluga Whale Liver 

(QC97LH2) and SRM 1946 Lake Superior Fish Tissue Samples .........................................I-1-6 

 Cadmium and Copper in Beluga Whale Liver (QC97LH2) ..................................................I-1 

 Mercury and Iron in Beluga Whale Liver (QC97LH2) .........................................................I-2 

 Selenium and Arsenic in Beluga Whale Liver (QC97LH2) ..................................................I-3 

 Cadmium and Mercury in SRM 1946 Lake Superior Fish Tissue ........................................I-4 

 Iron and Selenium in SRM 1946 Lake Superior Fish Tissue ................................................I-5 

 Arsenic in SRM 1946 Lake Superior Fish Tissue .................................................................I-6 

J. Evaluation of Laboratory Performance Using z- and p-scores..............................................J-1-3 

 z-score Plot for Beluga Whale Liver (QC97LH2).................................................................J-2 

 z-score Plot for SRM 1946 Lake Superior Fish Tissue .........................................................J-3 

K. Accuracy Assessment Using Normalization Factors.............................................................K-1-2 

L. Youden Two-Sample Plots for Pilot Whale Liver (QC91LH1) vs. Beluga 

Whale Liver (QC97LH2).......................................................................................................L-1-3 

 Cadmium and Copper ............................................................................................................L-1 

 Mercury and Iron ...................................................................................................................L-2 

 Selenium and Arsenic ............................................................................................................L-3 
iii

LIST OF TABLES 

Table 1: Interlaboratory Comparison Exercises Conducted for the MMHSRP from 

1991-2001 ..........................................................................................................................................6 

PART 1: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR ORGANIC 

CONTAMINANTS IN MARINE MAMMAL TISSUES 

Table 1.1: Laboratories Participating in the NIST/NOAA Interlaboratory 

Comparison Exercise Program for Organic Contaminants ...............................................................9 

Table 2.1: Target Analytes for the Second Annual NIST/NOAA Interlaboratory 

Comparison Exercise Program for Organic Contaminants and Trace Elements in 

Marine Mammal Tissues....................................................................................................................10 

Table 3.1: PCB congeners in Control Material IV (ng/g wet mass) Reported by 

the Participants the NIST/NOAA Interlaboratory Comparison Exercise Program 

for Organic Contaminants and Trace Elements in Marine Mammal Tissues....................................12 

Table 4.1: Organochlorine Pesticides in Control Material IV (ng/g wet mass) 

Reported by the Participants in the NIST/NOAA Interlaboratory Comparison 

Exercise Program for Organic Contaminants and Trace Elements in Marine 

Mammal Tissues ................................................................................................................................13 

Table 5.1: PCB Congeners in SRM 1945 (ng/g wet mass) Reported by the 

Participants in the NIST/NOAA Interlaboratory Comparison Exercise Program 

for Organic Contaminants and Trace Elements in Marine Mammal Tissues....................................14 

Table 6.1: Organochlorine Pesticides in SRM 1945 (ng/g wet mass) Reported by 

the Participants in the NIST/NOAA Interlaboratory Comparison Exercise 

Program for Organic Contaminants and Trace Elements in Marine Mammal 

Tissues................................................................................................................................................15 

PART 2: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR TRACE ELEMENTS 

IN MARINE MAMMAL TISSUES

Table 2.1: List of Laboratories Participating in the NIST/NOAA Interlaboratory 

Comparison Exercise Program for Trace Elements...........................................................................F-1 

Table 2.2: Individual Laboratory Results and Summary Statistics (mg/kg, wet 

mass) for Various Trace Elements in Pilot Whale Liver (QC91LH1), Beluga 

Whale Liver (QC97LH2) and SRM 1946 Lake Superior Fish Tissue Samples................................G-1-7 
iv

Table 3.2. Laboratory Means and Consensus Mean Summary Statistics (mg/kg, 

wet mass) for Various Trace Elements in Pilot Whale Liver (QC91LH1), Beluga 

Whale Liver (QC97LH2) and SRM 1946 Lake Superior Fish Tissue Samples................................H-1 

Table 4.2: Laboratory z-scores Computed for Beluga Whale Liver (QC97LH2) 

and SRM 1946 Lake Superior Fish Tissue Samples..........................................................................J-1 

Table 5.2: Laboratory p-scores Computed for Beluga Whale Liver (QC97LH2) 

and SRM 1946 Lake Superior Fish Tissue Samples..........................................................................J-1 

Table 6.2: Normalization Factors Used to Compute Normalized Laboratory and 

Consensus Mean Data........................................................................................................................K-1 

Table 7.2: Laboratory Means and Consensus Mean Summary Statistics (mg/kg, 

wet mass) Computed After the Application of the Normalization Procedure to 

Beluga Whale Liver (QC97LH2) and SRM 1946 Lake Superior Fish Tissue 

Samples..............................................................................................................................................K-2 
v

LIST OF FIGURES 

Figure 2.1: Using Youden Plots for Error Assessment......................................................................24 
vi

DISCLAIMER 

Certain commercial equipment or instruments are identified in this report to specify adequately 

the experimental procedures. Such identification does not imply recommendations or 

endorsement by the National Institute of Standards and Technology nor does it imply that the 

equipment or instruments are the best available for the purpose. 
vii

ABSTRACT 

The National Institute of Standards and Technology (NIST), in support of the National Oceanic 

and Atmospheric Administration’s Marine Mammal Health and Stranding Response Program 

(NOAA/MMHSRP) conducts annual interlaboratory comparison exercises for the determination 

of chlorinated pesticides, polychlorinated biphenyl congeners, and trace elements in marine 

mammal tissues. These exercises provide one mechanism for laboratories to evaluate their 

measurement quality and comparability for these constituents in marine mammal tissues. 

Results of the 2000 NIST/NOAA/MMHSRP Interlaboratory Comparison Exercise Program for 

Organic Contaminants and Trace Elements in Marine Mammal Tissues are presented in two 

parts in this report, after a brief historical introduction of the program. Part 1 focuses on the 

development and analytical results of the organic contaminant component of this exercise, while 

Part 2 describes the features and analytical results for the trace elements component. For the 

organic contaminant exercise, 13 laboratories determined the concentrations of selected 

polychlorinated biphenyl congeners (PCBs) and organochlorine pesticides in a homogenized 

blubber control material “Marine Mammal Quality Assurance Exercise Control Material IV” 

(Control Material IV) and Standard Reference Material (SRM) 1945 Organics in Whale Blubber. 

Seven laboratories participated in the 2000 trace element exercise, where each laboratory 

performed measurements on a suite of elements (Cu, Cd, Pb, Fe, Se, As, Hg, Ni, Ag, and Zn) in 

three NIST quality assurance materials: Pilot Whale Liver Homogenate I (QC91LH1), Beluga 

Whale Liver Homogenate II (QC97LH2), and candidate SRM 1946 Lake Superior Fish Tissue. 

This report includes the results reported by the participating laboratories, combined consensus 

data results, and summary statistics for each analyte in the samples. The numerical indices used 

to assess laboratory performance are also discussed. 
1

INTRODUCTION 

Laboratories measuring contaminants in the marine environment must assess the accuracy and 

precision of their measurements. Quality control of measurements made on marine 

environmental samples is vital to the accurate assessment of marine pollution and its effects on 

wildlife and human health. Often, reference materials are limited or not available for many 

marine matrices of interest (e.g., marine mammal tissues and marine fish). Consequently, marine 

resource management decisions may be based on subjective analytical results leading to potential 

environmental, health, or economic consequences. The National Institute of Standards and 

Technology’s (NIST’s) Analytical Chemistry Division has several programs to assess the data 

quality of laboratories and agencies performing chemical measurements on marine-related 

samples. NIST’s reference material production, interlaboratory comparison exercises, and 

environmental specimen banking all contribute to the accuracy of chemical measurements in the 

marine environment. 

NIST helps benchmark and improve the quality of analytical data gathered on the marine 

environment by administering annual interlaboratory comparison exercises. The largest exercise 

was initiated in 1987 and funded in part until 2000 by the National Oceanic and Atmospheric 

Administration (NOAA) National Status and Trends Marine Monitoring Program 

(NOAA/NS&T) (Cantillo and Parris, 1990, 1993; Cantillo 1995; Schantz et al., 1999). NIST 

provides mechanisms for assessing the interlaboratory and temporal comparability of data and 

for improving measurements of polycyclic aromatic hydrocarbons, polychlorinated biphenyl 

(PCB) congeners, and chlorinated pesticides in bivalve mollusk, sediment, and fish samples. In 

addition, the National Research Council of Canada, with support from NOAA, administers a 

similar interlaboratory comparison exercise for trace elements in marine environmental

materials. The NIST program for organic contaminants includes developing improved analytical 

methods, producing NIST Standard Reference Materials (SRMs) and other control materials, 

conducting annual interlaboratory comparison exercises, and coordinating workshops to discuss 

exercise results, thus providing a cooperative problem-solving forum for the participants. This 

program continues as the NIST Intercomparison Program for Organic Contaminants in the 

Marine Environment with partial support from fees paid by the participants. 

Through the NIST National Marine Analytical Quality Assurance Program and with support 

from the NOAA Marine Mammal Health and Stranding Response Program (MMHSRP), the 

interlaboratory comparison activities have been expanded to include analyses of marine mammal 

tissues. The 2000 NIST/NOAA Interlaboratory Comparison Exercise Program for Organic 

Contaminants and Trace Elements in Marine Mammal Tissues was modeled after the exercises 

described above. Specifically, this exercise was designed to help laboratories assess data 

comparability and quality relative to other groups providing measurements of organochlorine 

contaminants and trace elements in marine mammal tissues and to link these important 

measurements to a national metrology laboratory. The results of the exercises presented in this 

report should be useful both for assessing current methodology and reducing the variability of 

contaminant data reported on marine mammals. Future exercises will allow for the assessment 

of analytical data quality over time. This report summarizes the results of the 2000 exercise 

including methods used for analysis, data reported by the laboratories on the intercomparison 

materials, and numerical indices used to assess laboratory performance. 
2

Background on Interlaboratory Comparison Exercises and Associated Quality Assurance 

Activities Conducted by NIST for the MMHSRP 

In 1987, the NOAA National Marine Fisheries Service (NMFS), Office of Protected Resources, 

established the National Marine Mammal Tissue Bank (NMMTB) as part of the National 

Biomonitoring Specimen Bank maintained by NIST. The NMMTB was designed for the longterm cryogenic archiving of marine mammal tissue specimens for future retrospective chemical 

analysis. In 1992, the Marine Mammal Health and Stranding Response Act (Public Law 102-

587) formally established the NMMTB by legislation. NMFS implemented this Act by 

instituting the MMHSRP. Components of this program include marine mammal stranding 

networks, response to unusual mortality events, information management, real-time 

measurement of tissue contaminants, specimen banking, and analytical quality assurance. 

Within the MMHSRP, real-time monitoring of contaminants in marine mammals is conducted by 

NMFS’s Northwest Fisheries Science Center (NWFSC), Environmental Conservation Division. 

This monitoring includes analyses of samples collected specifically for real-time analysis and 

subsamples of banked specimens. NIST also analyzes aliquots of banked specimens to establish 

a baseline of concentration values for comparing with data generated by the NWFSC and other 

laboratories analyzing these specimens, and to monitor changes in analyte levels during 

specimen storage. Numerous other laboratories worldwide analyze marine mammal tissues for 

research and monitoring purposes. To assess the accuracy and comparability of results among 

NIST, NWFSC, and other laboratories, NIST in collaboration with NMFS developed a quality 

assurance (QA) program for analytical measurements of contaminants in marine mammal 

tissues. This QA program, described by Wise (1993), consists of (1) preparation, analysis, and 

distribution of marine mammal tissue control materials; (2) development of Standard Reference 

Materials (SRMs) for use in the analysis of marine mammal tissues; and (3) interlaboratory 

comparison exercises among laboratories analyzing marine mammal tissues. 

Preparation, Analysis, and Distribution of Control Materials 

 

Control materials, which are similar to the matrices being analyzed, are analyzed with regular 

samples with the results monitored to determine whether the analytical procedures are in control. 

The first control materials developed for the program were derived from liver and blubber tissues 

collected from pilot whales (Globicephala melaena) stranded in 1990 on Cape Cod, MA. 

Approximately 2 kg of each tissue were used to prepare tissue homogenates for use as analytical 

control materials and in interlaboratory comparison exercises. These homogenates are fresh 

frozen samples similar to marine mammal tissue samples routinely analyzed, rather than freezedried matrices frequently used as reference materials. The tissues were cryogenically pulverized 

and homogenized in Teflon mills to provide frozen powder-like materials (Zeisler et al., 1983). 

These two control materials were analyzed at NIST to determine concentrations of trace 

elements (Whale Liver Homogenate I) and organic contaminants (Whale Blubber Control 

Material) and to assess sample homogeneity (Wise et al., 1993). 

The concentrations of 40 trace elements plus methylmercury were determined in the Whale Liver 

Homogenate I using INAA, differential pulse and square wave stripping voltammetry, cold vapor 

atomic absorption spectroscopy (CVAAS) for Hg, and ion-exchange chromatography plus 
3

CVAAS (for methylmercury). Thirty PCB congeners and 16 chlorinated pesticides were 

determined in the Whale Blubber Control Material using gas chromatography-electron capture 

detection (GC-ECD) with both DB-5 and C-18 columns and gas chromatography-mass 

spectrometry (GC-MS) using a DB-5 column. The data resulting from analyses of both control 

materials, as well as a description of the analytical techniques and interpretation of the results, 

were published in Wise et al. (1993). 

Both the pilot whale liver homogenate (Whale Liver Homogenate I) and the Whale Blubber 

Control Material have been available for use by laboratories as control materials during the 

routine analyses of marine mammal tissues. Based on experience gained in the preparation and 

analyses of Whale Liver Homogenate I, a second liver homogenate control material (Whale Liver 

Homogenate II ) is being developed from livers collected in 1996 from beluga whales taken in 

Alaska native subsistence hunts. Whale Liver Homogenate II (fresh-frozen material) was 

distributed in 1997 to three laboratories participating in the interlaboratory comparison exercise 

on trace elements in marine mammal liver. This control material was also distributed to seven 

laboratories participating in the trace element part of the 2000 interlaboratory comparison 

exercise. 

Whale Liver Homogenate II represents a 5 kg subsample of 30 kg of beluga whale liver that was 

originally collected for the development of a marine mammal liver SRM. The Pilot Whale Liver 

Homogenate I will be nearly exhausted by the end of calendar year 2001 (some portion is being 

retained for sample stability monitoring); therefore, Whale Liver Homogenate II will be the 

primary control material used in future analyses for trace elements in marine mammal tissues. 

In the 1999 interlaboratory comparison exercise Whale Blubber Control Material was re-labeled 

Marine Mammal Blubber Control Material III, and distributed as an “unknown” to participants. 

Because the amount of this control material is now very limited, Whale Blubber Control 

Material IV is presently being developed as a replacement. Whale Blubber Control Material IV

was derived from blubber that was collected by the NMFS Beaufort Laboratory, from a single 

pilot whale that stranded in 1999 on Pea Island, North Carolina. This material was cryogenically 

homogenized and labeled, QC00-WB4 Whale Blubber Control Material IV, and was distributed 

as an “unknown” to participants in the 2000 interlaboratory comparison exercise for the organic 

analysis. 

Development of Standard Reference Materials (SRMs) 

One of the goals of the marine mammal QA program is to develop certified reference materials 

(CRMs) for validating analytical measurements of trace elements and organic contaminants in 

marine mammal tissues. At the beginning of the program, there were several CRMs available 

from NIST, the National Research Council of Canada (Ottawa, Canada), and the Community 

Bureau of Reference (Brussels, Belgium) for inorganic contaminants in marine tissues including 

oyster tissue, mussel tissue, fish muscle and liver tissue, and lobster tomalley. However, for 

organic contaminants such as PCB congeners and chlorinated pesticides, there were only mussel 

tissue, SRM 1974 Organics in Mussel Tissue (Mytilus edulis) and cod fish liver oil, SRM 1588 

Organics in Cod Liver Oil. SRM 1588, which serves as a suitable surrogate for a tissue extract 

with a high lipid content, had certified concentrations for 5 PCB congeners and 10 chlorinated 
4

pesticides and noncertified values for 20 additional PCB congeners and 4 additional chlorinated 

pesticides (Schantz et al., 1992). This material was reissued in 1998 as SRM 1588a and now 

has certified or reference values for over 80 organic contaminants. The mussel tissue SRM 

1974 was reissued as SRM 1974a and has certified or reference values for over 100 organic and 

inorganic constituents (Schantz et al., 1997). 

Because of the lack of organic reference materials, blubber was selected as the first priority 

tissue for development of SRMs as part of the marine mammal QA Program. The experience 

gained from the preparation and analysis of the pilot whale blubber control material (Wise et al.,

1993) was used to develop SRM 1945 Organics in Whale Blubber, a certified material that can 

be used for validating measurements of organic contaminants in marine mammal blubber. 

SRM 1945 was prepared from approximately 15 kg of blubber that was collected in September 

1991 from a stranding of pilot whales on Cape Cod, MA. The material was cryogenically 

pulverized and homogenized in the same manner as described for the control materials. The 

resulting frozen blubber homogenate was analyzed using three different analytical techniques 

based on GC-ECD on two stationary phases with different selectivities for the separation of PCB 

congeners and on GC-MS. The results of these three techniques provided certified 

concentrations for 27 PCB congeners (PCBs 18, 44, 49, 52, 66, 87, 95, 99, 101/90, 105, 110, 

118, 128, 138/163/164, 149, 151, 153, 156, 170/190, 180, 183, 187, 194, 195, 201, 206, and 209)

and 15 chlorinated pesticides (HCB, α-HCH, γ-HCH, heptachlor epoxide, oxychlordane, mirex, 

cis-chlordane, cis-nonachlor, trans-nonachlor, 2,4'-DDE, 4,4'-DDE, 2,4'-DDD, 4,4'-DDD, 2,4’-

DDT, and 4,4'-DDT). Noncertified values for two additional PCB congeners (PCB 28 and 31) 

and chlorinated pesticides (dieldrin and β-HCH) are available.

Analytical data for the certification of PCBs and chlorinated pesticides in SRM 1945 were 

published by Schantz et al. (1995). SRM 1945, which represents the most highly characterized 

natural-matrix SRM with respect to these organic compounds, complements the other frozen 

tissue SRM (e.g., SRM 1974a) by providing concentrations that are generally a factor of 10 to 

100 times higher for the PCB congeners and chlorinated pesticides. Solvent extraction of the 

whale blubber produces an oil matrix similar to that of the cod liver oil SRM; however, the 

concentrations of PCB congeners and pesticides in SRM 1945 are generally 2 to 3 times lower 

than the NIST cod liver oil SRM except for the PCB congeners with higher degrees of 

chlorination, which have concentrations similar to the cod liver oil. 

Additional concentration values for constituents not originally measured in SRM 1945 (i.e.,

dioxins, furans, non-ortho PCBs, and polyhalogenated diphenyl ethers) have been provided for 

this material by the National Wildlife Research Center, Canadian Wildlife Service (CWS). 

These data are found in CWS Lab Services Section Reports CHEM-OC-97-40, CHEM-PCDD98-1, and CHEM-PCDD-98-4). SRM 1945 was found to have relatively high amounts of twelve 

polybrominated diphenyl ethers (tetra through hepta congeners). More recently, measurements 

have been made by NIST on additional analytes in SRM 1945, including congeners of 

polychlorinated naphthalenes (PCNs) and co-planar PCBs (77, 126, 169). 

The low relative uncertainties associated with the majority of analyte concentrations (5 % to 10 

%) and the extensive list of certified analytes makes SRM 1945 a valuable resource for 
5

validating analytical methods for the determination of halogenated compounds in marine 

mammal blubber and other high lipid-containing materials.

 

Interlaboratory Comparison Exercises 

An interlaboratory comparison made on common, well-homogenized reference samples is one 

method to assess and improve data comparability. Such exercises currently involve the analysis 

of an unknown sample, a control material, and a NIST-traceable SRM by the participants. A list 

of analytes to be compared among the laboratories is provided to the participants. Participants 

submit their results to the NIST coordinator who evaluates data comparability using the 

performance measures recommended by the International Union of Pure and Applied Chemistry 

(IUPAC, 1993). Reports on the comparability evaluation are provided to the participants. NIST 

then conducts a workshop with the participants to discuss the results and ways to improve 

comparability. 

Table 1 summarizes several important aspects of the interlaboratory comparison exercises 

conducted from 1991 to date, including target analytes, matrix samples, and the number of 

participating laboratories. The first exercise was conducted in 1991-92 and consisted of the 

distribution of the liver and blubber control materials to NWFSC and several other laboratories 

for analysis, i.e., Department of Fisheries and Oceans (DFO) Canada in Winnipeg, the 

Geochemical and Environmental Research Group (GERG) at Texas A&M University, and the 

Department of Analytical and Environmental Chemistry at the University of Ulm in Germany. 

In 1992, three laboratories (NIST, DFO Canada in Winnipeg, and the Department of Analytical 

and Environmental Chemistry at the University of Ulm in Germany) analyzed blubber 

subsamples from four to six beluga whales, the pilot whale blubber control material, and SRM 

1588 in an interlaboratory exercise to compare results of analyses for PCB congeners and 

chlorinated pesticides. The analytical methods used by these three laboratories are described in 

Schantz et al. (1996). To minimize variability resulting from the source of calibration solutions, 

all three laboratories used common solutions to prepare calibration standards. Different internal 

standards and volume correction standards were used by each laboratory. Each laboratory used 

its preferred methods of extraction (Soxhlet extraction at NIST, ball-milling extraction at DFO, 

and column extraction at Ulm). All three laboratories used a size-exclusion chromatography 

cleanup, but with different columns, to remove the lipid material from the extracts and separated 

the PCB congeners from the majority of the pesticides as part of the cleanup procedures. GCECD was used by all three laboratories for the final analysis employing different columns. The 

results of this exercise were published in Schantz et al. (1996). 
6

Table 1: Interlaboratory comparison exercises conducted for the MMHSRP from 1991-2001. 

Dates Analytes Matrices Objective Participants 

1991-92 PCBs/Cl 

pesticides1 

Trace 

Elements 

Whale blubber 

Whale liver CM2

Laboratory 

comparability 

Analytical control 

NIST;NWFSC;DFO3

 Canada; 

Texas A&M Univ.; Univ. Ulm 

NIST;NWFSC 

1992-93 PCBs/Cl 

pesticides 

Whale blubber; 

whale blubber CM 

Laboratory 

comparability 

NIST; DFO Canada; Univ. Ulm 

1993-1994 PCBs Whale blubber; 

whale blubber CM 

SRM 

development 

NIST;NWFSC; DFO Canada; Texas 

A&M Univ.; Arthur D. Little; NW 

Aquatic Sciences; Univ. Ulm 

1993-1997 PCBs/Cl 

pesticides 

and Trace 

Elements 

Whale / seal liver Sample 

comparability 

NIST; NWFSC 

1997-1998 Trace 

Elements 

Whale liver Laboratory

comparability and 

CM development 

NIST;NWFSC; Texas A&M Univ., 

Veterinary College 

1999 PCBs/Cl 

Pesticides 

SRM 1945 Organics 

in Whale Blubber 

Whale blubber CM 

Laboratory

comparability 

10 laboratories 

2000 PCBs/Cl 

Pesticides 

Trace 

Elements 

SRM 1945 Organics 

in Whale Blubber 

Whale Livers 

(QC91LH1) 

(QC97LH2) 

SRM 1946 Lake 

Superior Fish Tissue 

Laboratory 

comparability and 

program 

expansion 

13 laboratories (organics) 

7 laboratories (trace elements) 

2001 

(projected) 

PCBs/Cl 

Pesticides 

Trace 

Elements 

SRM 1945 and 

Whale blubber CM 

Whale Livers 

(QC91LH1) 

(QC97LH2) 

Candidate 

SRM 1947 Lake 

Michigan Fish Tissue 

Laboratory

comparability and 

program 

expansion 

21 laboratories (organics)4

31 laboratories (trace elements)4

1

Chlorinated pesticides 

2

Control material 

3

Department of Fisheries and Oceans 

4

Projected number of laboratories based on jars of material shipped to participants 
7

In 1993, two intercomparison exercises were initiated. The first exercise focused on determining 

PCB congeners and chlorinated pesticides in blubber tissue using the blubber homogenate 

prepared as a proposed SRM (see discussion above). This material was distributed to NWFSC 

and several other laboratories for analysis (i.e., DFO Canada, GERG, Northwestern Aquatic 

Sciences in Newport, OR, Arthur D. Little in Cambridge, MA, and University of Ulm). The 

second QA activity involved a "sample split" between NIST and NWFSC of blubber and liver 

samples from three marine mammals for both inorganic and organic analyses. These tissue 

samples were from specimens collected as part of the tissue banking and monitoring components 

of the program. In the past, for many of the liver and blubber specimens in the NMMTB, similar 

tissue samples were collected using NWFSC protocols and shipped to NWFSC for analysis as 

part of the monitoring effort. For this intercomparison exercise, NIST homogenized the selected 

liver and blubber samples from the tissue bank and provided a subsample of each homogenate to 

NWFSC. NIST and NWFSC analyzed tissue homogenate subsamples from the bank (liver for 

trace elements and blubber for PCBs and pesticides). The NWFSC analyzed the "monitoring" 

liver and blubber samples from the same animals. This provided an assessment of 

interlaboratory comparability on the same tissue homogenates and the comparability of the 

analyses of banked and the monitoring specimens collected from the same animals. This QA 

activity was an informal exercise only; the results have not been published. 

In 1995 NIST, in collaboration with NOAA, formally instituted the National Marine Analytical 

Quality Assurance Program (NMAQAP). The mission of this program is to expand QA and 

specimen banking activities in marine environmental research and monitoring. To help 

accomplish the NMAQAP mission, a NIST satellite laboratory was established in Charleston, 

SC, in association with the NOAA Center for Coastal Environmental Health and Biomolecular 

Research (CCEHBR). The NMMTB is housed both at the NIST-Gaithersburg and at the NISTCharleston facilities. NIST-Charleston provides the primary infrastructure for the marine 

mammal QA program and the NMMTB. 

In 1997, an interlaboratory comparison exercise on trace elements in beluga whale liver sample 

splits was initiated among NIST-Gaithersburg, NWFSC, and the Texas A&M University 

Veterinary Medical Center. All three laboratories were involved in analyzing marine mammal 

tissues collected in Arctic Alaska. For this exercise, sample splits of beluga whale liver tissues 

collected during the 1996 subsistence hunts in Alaska were provided to the participants, as well 

as the pilot whale liver control material (Whale Liver Homogenate I) and the new beluga whale 

liver control material (Whale Liver Homogenate II). 

The 1999 exercise included only laboratories conducting organic analyses. The 10 participating 

laboratories (NIST-Gaithersburg, NIST-Charleston, CCEHBR, NWFSC, GERG, Mississippi 

State Chemistry Laboratory, University of Connecticut, National Lab for Environmental Testing 

[Canada], Ehime University [Japan], and University of Utah) measured PCB congeners and 

organochlorine pesticides in SRM 1945 and in the “unknown,” Marine Mammal Blubber

Control Material III (this material is described above in the control material section). Also in 

1999, the program began holding meetings of participants in conjunction with the annual 

meeting of the Society of Environmental Toxicology and Chemistry (SETAC). 
8

Participation in the 2000 exercise included laboratories conducting both organic analyses (13 

laboratories) and inorganic analyses (7 laboratories). The description and results of this exercise 

are presented in Parts 1 and 2 of this report. In 2001, there were approximately 21 laboratories 

participating in the organic exercise and 31 laboratories participating in the inorganic exercise. 

Expanding the number of laboratories provides an essential benefit for the participants in

yielding higher quality consensus data. NIST also benefits from the preliminary concentration 

data and information gained on the candidate SRM materials that are routinely inserted into the 

exercises. 

The QA program performs a major function in maintaining the quality of data resulting from the 

analysis of NMMTB specimens. Scientists requesting specimens from the bank for retrospective 

studies must demonstrate their analytical capabilities through appropriate QA activities, 

including participation in the NIST-administered QA program. In addition, NMFS requires that 

all researchers analyzing marine mammal tissues for contaminants under NMFS funding be 

participants in this program. This requirement ensures that the analytical results from marine 

mammal monitoring and research programs are of high quality and comparable. 

 

PART 1: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR ORGANIC 

CONTAMINANTS IN MARINE MAMMAL TISSUES 

Materials Used in the Exercise 

The exercise used two materials that were provided to 16 laboratories, of which 13 submitted 

data (Table 1.1). Participants were asked to make three measurements each on two materials: 

SRM 1945 Organics in Whale Blubber and “Marine Mammal Quality Assurance Exercise 

Control Material IV” (Control Material IV). Details on the preparation and certification of SRM 

1945 are given in Schantz et al. (1995). The control material was prepared from blubber taken 

from a 350 cm female pilot whale. The animal stranded alive on the beach at Pea Island, NC 

(35° 69.228’ N 75° 48.359’ W) and was euthanized on November 18, 1999. Approximately 50 

kg of blubber was excised, wrapped in aluminum foil, and shipped to the NIST Charleston 

Laboratory on February 18, 2000 inside a biological dry shipper. At NIST Charleston, the 

blubber tissue was stored in a liquid nitrogen (LN2) vapor phase freezer at –150 °C until prepared 

for this exercise. The material was trimmed on Teflon sheeting using a titanium knife. A total of 

7 kg of trimmed blubber was placed in Teflon bags, which were heat sealed and shipped to NIST 

Gaithersburg for cryohomogenization according to established procedure (Zeisler et al., 1983). 

After homogenization, the material was placed inside a Teflon bag and blended manually by 

repeated inversion. The blended material was bottled as 12 g subsamples in glass jars and stored 

at -80 °C. One bottle of this material along with one bottle of SRM 1945 were sent either on dry 

ice or using a biological dry shipper via overnight express to each participating laboratory. 
9

Table 1.1: Laboratories participating in the NIST/NOAA Interlaboratory Comparison Exercise 

Program for Organic Contaminants and Trace Elements in Marine Mammal Tissues. 

National Laboratory for Environmental Testing Energy and Geoscience Institute

National Water Research Institute Department of Civil and Environmental Engineering

Environment Canada University of Utah

Canada Centre for Inland Waters 423 Wakara Way, Suite 300

867 Lakeshore Road Salt Lake City Utah 84108

Burlington, Ontario

Canada Geochemical and Environmental Research Group 

Texas A&M University 

MS State Chemical Lab 833 Graham Road 

P.O. Box CR TAMU Mail Stop 3149 

MS State, MS 39762 College Station, Texas 77845 

Center for Marine Environmental Studies (CMES),

Ehime University National Institute of Standards and Technology

Tarumi 3-5-7, Matsuyama, Ehime 790-8566 Analytical Chemistry Division

Japan 100 Bureau Drive

Gaithersburg, MD 20899-8392

National Marine Fisheries Service

Northwest Fisheries Science Center NOAA/CCEHBR at Charleston

2725 Montlake Blvd East 219 Fort Johnson Road

Seattle, WA 98112-2097 Charleston, SC 29412

Department of Environmental Sciences Fisheries and Oceans Canada

Kumamoto University Institute of Ocean Sciences

2-39-1 Kurokami, Kumamoto, 860-8555 9860 West Saanich Road

Japan Sidney, B.C. V8L-4B2

Canada

Environmental Research Institute

University of Connecticut National Institute of Standards and Technology

Storrs, CT 06269 Analytical Chemistry Division

Charleston Laboratory

University of Barcelona 219 Fort Johnson Road

Av. Diagonal 645 Charleston, SC 29412

08071 Barcelona

Spain

Exercise Requirements and Target Analytes 

A suite of analytes was chosen for the exercise based on those used in the NIST/NOAA/NS&T 

exercise and several additional analytes were included to broaden this list (Table 2.1). 

Laboratories were requested to make triplicate measurements of these compounds in each of the 

materials and report their data using a data template provided by NIST. Laboratories were also 

asked to provide results from additional analytes, such as coplanar PCBs or chlorobenzenes that 
10

were determined in the two materials. Results from the exercise were discussed during a 

workshop held in conjunction with the 2000 Society of Environmental Toxicology and 

Chemistry annual meeting held in Nashville, TN. 

Table 2.1: Target analytes for the second annual NIST/NOAA Interlaboratory Comparison 

Exercise Program for Organic Contaminants and Trace Elements in Marine Mammal Tissues. 

Pesticides PCB Congeners Congener Substitution

2,4'-DDT 18 2,2',5-trichlorobiphenyl

4,4'-DDT 28 2,4,4'-trichlorobiphenyl

2,4'-DDE 31 2,4',5-trichlorobiphenyl

4,4'-DDE 44 2,2',3,5'-tetrachlorobiphenyl

2,4'-DDD 49 2,2',4,5'-tetrachlorobiphenyl

4,4'-DDD 52 2,2',5,5'-tetrachlorobiphenyl

HCB 66 2,3',4,4'-tetrachlorobiphenyl

α-HCH 87 2,2',3,4,5'-tetrachlorobiphenyl

γ-HCH 95 2,2',3,5',6-tetrachlorobiphenyl

β-HCH 99 2,2',4,4',5-tetrachlorobiphenyl

heptachlor epoxide 101 2,2',4,5,5'-tetrachlorobiphenyl

cis-chlordane 105 2,3,3',4,4'-tetrachlorobiphenyl

trans-chlordane 118 2,3',4,4',5-tetrachlorobiphenyl

oxychlordane 128 2,2',3,3',4,4'-hexachlorobiphenyl

cis-nonachlor 132 2,2',3,3',4,6'-hexachlorobiphenyl

trans-nonachlor 138 2,2',3,4,4',5'-hexachlorobiphenyl

dieldrin 149 2,2',3,4',5',6-hexachlorobiphenyl

mirex 151 2,2',3,5,5',6-hexachlorobiphenyl

153 2,2',4,4',5,5'-hexachlorobiphenyl

156 2,3,3',4,4',5-hexachlorobiphenyl

170 2,2',3,3',4,4',5-heptachlorobiphenyl

180 2,2',3,4,4',5,5'-heptachlorobiphenyl

183 2,2',3,4,4',5',6-heptachlorobiphenyl

187 2,2',3,4',5,5',6-heptachlorobiphenyl

194 2,2',3,3',4,4',5,5'-octachlorobiphenyl

195 2,2',3,3',4,4',5,6-octachlorobiphenyl

201 2,2',3,3',4,5,5',6'-octachlorobiphenyl

206 2,2',3,3',4,4',5,5',6-nonachlorobiphenyl

209 2,2',3,3',4,4',5,5',6,6'-decachlorobiphenyl
11

Evaluation of the Exercise Results 

Determination of Laboratory Analyte Means 

Each laboratory reported the results of their analyses (Sample 1, Sample 2, and Sample 3) and 

the mean for each laboratory was calculated. Non-numerical results were reported as “NA” (not 

analyzed). None of the target analytes were below the limit of detection for the participating 

laboratories (Tables 3.1-6.1 and Appendix A). 

Establishment of Consensus Values 

The following guidelines were used by NIST for establishing the “assigned values” or 

“consensus values” for the exercise. The consensus values for Control Material IV were the 

mean of all the reported laboratory means for a compound after the data were first screened by a 

Grubb’s Single Iteration Outlier Test (Motulsky, 1997). Generally, most or all the values were 

included in the determination of the consensus value. The target values for the SRM were the 

certified values, reference values, or the consensus values from the 1999 exercise where SRM 

1945 was also analyzed (Tables 5.1 and 6.1). In the NIST/NOAA/NS&T exercise, the assigned 

values for the unknown material were calculated based on the performance of each laboratory on 

the SRM. If the laboratory was within ± 30% of the SRM value, their values for the 

corresponding unknown were used to determine the consensus value. This approach was not 

used in the present exercise for two reasons. First, if the SRM comparison method using ± 30% 

is used, nearly one-third of the data are excluded from the calculation of the control material 

consensus value. Relaxing the ± 30% criterion to ± 50% still results in the rejection of 

approximately 20% of the data that could be used to calculate the consensus value. Second, the 

concentration of Control Material IV was significantly greater than SRM 1945. For instance, the 

concentration of PCB 153 was 35 times greater in Control Material IV than in SRM 1945. 

Hence there was concern regarding the performance on the SRM being reflective of the 

performance on the control material. 

 

Reported Results 

Laboratories were assigned a numerical identification code based on the order in which data 

were received with the exception of NIST-Charleston, which is Laboratory 1. The same code 

was used for both materials. The results from the analysis of Control Material IV and SRM 1945 

are summarized in Tables 3.1-6.1. Appendix A shows the tabulated results from the individual 

laboratories for both materials and the results are shown graphically in Appendix B. Appendix C 

gives the methods used for analysis by each laboratory and Appendix D shows data for 

additional analytes. 
12

Control Material IV Laboratory Reported Values Consensus ValuesCongener 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean 1 SD n Mean n 1 SD 95%CI18 9.74 9.09 16.3 42.7 14.9 14.4 NA NA 5.14 22.4 NA 13.3 12.9 16.1 10 10 13.1 9 4.9 3.2

28 36.0 22.1 37.0 21.0 24.7 20.7 67.2 NA 35.9 NA 34.0 30.4 32.3 32.9 13 11 29.4 10 6.6 4.1

31 6.99 2.35 NA 11.7 2.6 NA NA NA 1.54 NA NA NA 3.05 4.71 3.9 6 4.71 6 3.9 3.144 31.8 29.2 36.3 53.3 32.7 28.2 40.9 22.3 41.7 48.0 NA 40.1 30.5 36.3 8.9 12 36.3 12 8.9 5.049 77.3 86.5 89.4 150 89.6 NA 134 77.2 113 80.6 NA 121 97.7 102 25 11 102 11 25 1552 267 282 294 403 284 228 417 204 362 245 283 222 274 290 67 13 290 13 67 3666/95* 578 365 615 1260 552 267 851 394 600 498 483 647 603 593 248 13 538 12 152 86

87 207 204 246 NA 180 NA 291 124 249 NA NA 240 189 214 49 9 214 9 49 3299 644 438 770 260 666 NA 1059 571 863 575 NA 1017 619 680 237 11 680 11 237 140101 (+90) 1036 1110 595 1967 909 1102 1684 655 1386 897 676 1067 1066 1088 397 13 1088 13 397 216105 324 302 301 497 387 349 657 303 444 302 358 249.9 328 369 109 13 345 12 69 39

118 1097 1133 57.6 1487 1167 1296 2585 1050 1374 1053 949 1032 1106 1184 540 13 1067 12 353 200

128 411 437 392 917 457 494 489 294 556 435 764 576 405 510 166 13 510 13 166 90132 NA NA NA 183 457 NA 1336 691 12560 265 NA NA NA 2582 4905 6 587 5 462 405

138 (+163+164) 4475 4750 1253 6577 4643 3595 6793 4150 7689 3107 2867 5349 3905 4550 1755 13 4550 13 1755 954149 2261 1033 2303 3763 3130 NA 2930 1557 3216 1803 1535 2476 2259 2355 801 12 2355 12 801 453151 701 534 720 980 822 NA 844 404 938 573 518 931 613 715 189 12 715 12 189 107153 7424 6723 6781 7353 7860 6304 10288 6137 12465 4890 5420 8932 7525 7546 2044 13 7546 13 2044 1111156 243 189 218 627 214 NA 364 159 244 189 342 400 228 285 131 12 254 11 79 47

170 (+190) 1274 1303 663 2063 1137 1335 1444 884 1221 1177 1786 1499 1162 1304 357 13 1304 13 357 194180 3664 3740 3851 6337 3770 2773 4885 3313 4013 2810 2793 4049 3355 3796 967 13 3585 12 621 351183 777 NA 758 1390 774 NA 72.2 783 867 637 NA 624 775 746 319 10 746 10 319 198187 2408 2560 53.5 3657 2917 2273 1108 1957 2858 1727 1748 2690 2393 2181 904 13 2181 13 904 491194 259 301 383 323 387 NA 350 210 365 300 265 356 250 312 58 12 312 12 58 33195 88.9 96.0 137 123 142 101 96.1 48.0 93.2 NA 345 125 90.5 124 74 12 104 11 27 16201 46.7 NA 64 NA NA NA 398 NA 510 337 512 73.3 46.3 249 212 8 249 8 212 147206 24.7 27.0 38.5 52.3 45.3 18.2 NA NA 35.2 28.6 31 53.1 29.1 34.8 11 11 34.8 11 11 6.7209 12.3 9.02 14.6 18.3 NA 20.7 NA NA 14.8 12.8 NA 22.9 11.6 15.2 4.5 9 15.2 9 4.5 3.066 105 105 NA 463 113 NA 224 109 86.2 92.3 NA 73.4 136 151 117 10 116 9 44 29

95 473 259 NA 797 439 NA 627 285 513 405 NA 573 467 484 158 10 484 10 158 98

Table 3.1.

*summed by coordinator if reported separatelyOutliers are in bold; not used to calculate the consensus value

 PCB congeners in Control Material IV (ng/g wet mass) reported by the participants the NIST/NOAA Interlaboratory 

Comparison Exercise Program for Organic Contaminants and Trace Elements in Marine Mammal Tissues.
13

Control Material IV Laboratory Reported Values Consensus ValuesCompound 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean 1 SD n Mean n 1 SD 95%CI2,4’-DDT 1031 971 1026 1263 2043 1570 NA NA NA NA 1310 1159 1035 1268 347 9 1171 8 202 140

4,4’-DDT 2581 1750 2310 2493 5027 2518 4157 1940 NA 2433 1697 2231 2887 2669 981 12 2669 12 981 5552,4’-DDE 349 350 384 417 644 544 NA NA NA NA 440 332 344 423 106 9 423 9 106 704,4’-DDE 24361 20600 19967 24533 20533 22360 52569 29000 NA 12400 16514 22670 28819 24527 9984 12 21978 11 4884 28862,4’-DDD 266 260 363 338 303 1130 NA NA NA 273 NA 447 284 407 278 9 317 8 64 44

4,4’-DDD 2033 1367 1764 1647 1493 2003 2477 1353 NA 2060 1156 1788 2029 1764 379 12 1764 12 379 214HCB 246 264 199 223 249 219 330 298 NA 218 271 235 243 250 37 12 250 12 37 21alpha-HCH 9.54 5.89 NA 5.93 5.81 10.1 8.47 6.44 NA 5.59 NA 2.28 10.4 7.05 2.5 10 7.05 10 2.5 1.6beta-HCH 25.8 37.6 NA 42.0 62.5 38.5 50.9 40.7 NA 45.7 NA 30.4 25.2 39.9 11 10 39.9 10 11 7.1gamma-HCH 4.34 5.43 NA 4.73 6.13 5.50 6.69 4.78 NA 5.36 NA 3.72 3.52 5.02 1.0 10 5.02 10 1.0 0.62Heptachlor Epoxide 54.5 71.1 71.7 103 74.8 63.2 NA 66.7 NA 55.5 NA 95.0 53.0 70.9 17 10 70.9 10 17 10Cis-Chlordane 88.0 101 88.4 119 104 87.5 129 103 NA 77.6 NA 56.1 86.9 94.5 20 11 94 11 20 12Trans-Chlordane 7.04 7.13 8.00 NA 18.5 25.4 24.3 37.0 NA NA NA 9.39 13.4 16.7 10 9 16.7 9 10 6.8Oxychlordane 113 74.9 NA 60.7 74.8 64.8 103 104 NA 35.8 NA 48.7 91.0 77.1 25 10 77.1 10 25 16Cis-Nonachlor 137 159 143 198 240 194 272 196 NA 142 NA 172 128 180 46 11 180 11 46 27Trans-Nonachlor 387 455 431 582 576 798 801 530 NA 294 NA 392 377 511 167 11 511 11 167 99Dieldrin 347 395 394 412 391 544 NA 466 NA 362 NA 439 NA 417 60 9 417 9 60 39Mirex 36.2 43.9 48.8 45.3 87.9 57.3 NA NA NA 43.4 NA 61.3 44.4 52.1 15 9 47.6 8 8.1 5.6

Lipid 67.0 64.7 66.2 68.7 76.1 70.2 71.0 66.6 71.4 65.7 65.9 80.8 68.9 69.5 4.6 13 69.5 13 4.6 2.5

Outliers are in bold; not used to calculate the consensus value

Table 4.1: Organochlorine pesticides in Control Material IV (ng/g wet mass) reported by the participants in the NIST/NOAA InterlaboratoryComparison Exercise Program for Organic Contaminants and Trace Elements in Marine Mammal Tissues.
14

SRM 1945 LaboratoryCongener 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean 1 SD 95% CI n Comment18 4.90 3.30 4.90 5.27 3.29 4.27 NA NA 1.65 4.47 NA 9.07 4.67 4.08 1.3 0.83 9 4.48 ± 0.88 certified value

28 14.2 8.87 13.5 14.1 11.3 10.6 23.1 NA 17.8 NA 15.0 18.5 14.0 14.6 4.0 2.4 11 14.1 ± 1.4 reference value31 5.35 3.95 NA 5.57 2.17 NA NA NA 4.24 NA NA 4.06 3.28 4.09 1.2 0.86 7 3.12 ± 0.69 reference value44 14.5 9.87 22.0 15.4 11.2 11.2 12.6 10.2 15.4 17.2 NA 16.9 12.5 14.1 3.5 2.0 12 12.2 ± 1.4 certified value49 16.7 15.5 16.1 22.4 22.3 NA 21.3 17.4 20.2 17.4 NA 26.8 18.4 19.5 3.5 2.0 11 20.8 ± 2.8 certified value52 39.4 37.4 52.6 45.2 39.0 38.6 45.3 33.0 45.3 36.5 38.9 25.4 41.8 39.9 6.6 3.6 13 43.6 ± 2.5 certified value

66/95* NA NA 80.5 NA NA 23.1 NA NA NA NA 50.9 NA NA 51.5 29 33 3 57.4 sum of the cert. values87 23.4 22.8 29.1 NA 20.3 NA 22.9 15.3 26.4 NA NA 32.9 15.9 23.2 5.7 3.7 9 16.7 ± 1.4 certified value99 56.8 56.1 68.2 53.5 56.9 NA 69.2 51.1 66.9 50.8 NA 105 44.8 57.4 8.2 4.8 11 45.4 ± 5.4 certified value

101 (+90) 77.6 84.3 47.9 104 76.0 66.8 97.7 53.3 95.5 79.6 68.0 114 67.3 79.4 19 11 13 65.2 ± 5.6 certified value105 31.0 24.3 24.0 36.3 30.9 25.0 36.7 24.3 34.6 33.8 29.8 20.9 31.4 29.5 5.2 2.9 13 30.1 ± 2.3 certified value

118 74.3 70.8 95.8 69.6 74.7 75.3 133 72.6 96.3 72.5 84.2 85.9 76.7 79.1 9.3 5.1 13 74.6 ± 5.1 certified value

128 23.4 18.7 15.4 40.3 24.0 24.2 17.1 13.7 23.8 24.4 38.6 49.2 23.7 25.9 10 5.7 13 23.7 ± 1.7 certified value132 NA NA NA 7.23 21.1 NA 41.4 27.7 347 NA NA NA NA 88.9 145 127 5 29.1 ± 6.0 consensus of 99 QA138 (+163+164) 141 165 55.2 90 129 123 192 156 234 121 144 247 129 148 53 29 13 132 ± 7.4 certified value149 77.4 78.3 90.2 82.6 85.8 NA 81.5 58.2 108 69.9 72.9 91.2 101 83.1 14 7.7 12 107 ± 8.4 certified value151 24.7 23.2 26.6 34.8 31.1 NA 24.4 15.3 32.3 22.6 30.8 40.4 28.0 27.8 6.6 3.7 12 28.7 ± 5.2 certified value

153 230 207 255 290 192 206 253 202 347 180 249 397 215 248 64 35 13 213 ± 19 certified value156 12.9 8.82 9.43 26.9 11.7 NA 15.7 8.99 11.6 10.5 15.1 14.0 10.5 11.7 2.4 1.4 11 10.3 ± 1.1 certified value170 (+190) 40.4 35.8 23.8 44.1 40.3 38.6 36.5 28.9 39.8 42.1 50.3 77.4 41.1 38.5 6.9 3.9 12 40.6 ± 2.6 certified value

180 134 116 174 175 136 116 160 143 170 134 138 244 112 142 23 13 12 107 ± 5.3 certified value

183 35.2 31.1 34.0 42.5 36.4 NA NA 36.9 44.9 29.9 NA 31.4 35.8 35.8 4.8 3.0 10 36.6 ± 4.1 certified value187 110 111 123 110 117 103 41 100 159 97.7 101 157 103 110 29 16 13 105 ± 9.1 certified value194 50.1 42.2 72.4 48.1 58.3 NA 64.9 43.0 61.7 55.8 36.9 78.5 41.1 54.4 13 7.4 12 39.6 ± 2.5 certified value195 14.4 6.60 11.5 9.90 13.3 12.3 8.29 5.22 9.40 NA 25.1 38.0 16.8 12.1 5.5 3.3 11 17.7 ± 4.3 certified value

201 13.0 NA 14.0 NA NA NA 68.9 NA 96.9 65.2 82.0 20.6 16.3 47.1 35 24 8 17.0 ± 0.89 certified value206 42.8 31.7 58.8 52.8 54.3 34.1 54.2 NA 56.7 43.3 36.0 65.5 32.5 46.9 12 6.6 12 31.1 ± 2.7 certified value

209 18.4 8.4 21.6 12.3 NA 15.4 26.2 NA 21.7 18.4 NA 27.6 12.4 18.3 6.2 3.9 10 10.6 ± 1.1 certified value66 37.0 20.3 NA 37.0 21.1 NA 37.3 22.8 25.2 19.3 NA 20.7 21.8 26.2 7.7 4.7 10 23.6 ± 1.6 certified value95 36.3 35.3 NA 49.0 33.4 NA 36.7 25.1 39.0 33.8 NA 49.9 31.2 37.0 7.6 4.7 10 33.8 ± 1.7 certified value*summed by coordinator if reported separatelyOutliers are in bold; not used to calculate the consensus value

Target

Value

Table 5.1: PCB congeners in SRM 1945 (ng/g wet mass) reported by the participants in the NIST/NOAA Interlaboratory Comparison Exercise 

Program for Organic Contaminants and Trace Elements in Marine Mammal Tissues.
15

SRM 1945 LaboratoryCompound 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean 1 SD 95% CI n Comment2,4’-DDT 69.0 67.4 78.5 78.7 137 122 NA NA NA NA 88.2 98.4 96.3 92.8 24 15 9 106 ± 14 certified value4,4’-DDT 224 162 265 258 286 239 357 237 NA 313 163 248 232 249 55 31 12 245 ± 15 certified value2,4’-DDE 15.7 12.3 15.8 12.0 31.3 15.0 NA NA NA NA 46.7 9.14 13.1 15.5 6.7 4.7 8 12.3 ± 0.87 certified value

4,4’-DDE 502 476 526 519 487 533 599 720 NA 379 601 540 477 530 84 47 12 445 ± 37 certified value2,4’-DDD 24.4 24.9 24.7 21.8 13.7 24.5 NA NA NA 16.9 NA 24.8 19.0 21.6 4.2 2.7 9 18.1 ± 2.8 certified value4,4’-DDD 121 117 148 143 115 124 172 120 NA 124 99 122 115 127 19 11 12 133 ± 10 certified valueHCB 31.0 27.6 26.2 22.7 26.6 26.7 24.3 27.6 NA 24.3 32.7 29.5 32.0 27.6 3.2 1.8 12 32.9 1.7 certified valuealpha-HCH 17.2 15.9 16.8 15.6 9.3 16.2 18.4 15.3 NA 12.6 NA 8.09 17.7 14.8 3.4 2.0 11 16.2 ± 3.4 certified valuebeta-HCH 3.34 6.34 NA NA 3.07 5.67 2.88 2.05 NA 2.47 NA 7.77 5.85 4.38 2.0 1.3 9 8.00 ± 1.4 reference valuegamma-HCH 4.74 NA NA 3.10 3.81 3.43 4.24 3.24 NA 4.47 NA 4.36 3.17 3.84 0.6 0.41 9 3.3 ± 0.81 certified valueHeptachlor Epoxide 12.8 10.1 13.3 15.4 10.7 10.8 NA 12.4 NA 7.85 NA 7.67 10.7 11.2 2.4 1.5 10 10.8 ± 1.3 certified valueCis-Chlordane 51.6 52.0 48.6 40.6 39.3 47.7 53.7 51.7 NA 34.6 NA 40.2 44.7 45.9 6.4 3.8 11 46.9 ± 2.8 certified valueTrans-Chlordane 12.0 10.3 NA 8.7 9.9 13.0 NA 17.5 NA 13.1 NA 10.3 12.4 11.9 2.6 1.7 9 12.9 ± 3.5 consensus of 99 QAOxychlordane 24.5 25.9 NA 18.9 18.7 21.9 25.0 31.0 NA 14.3 NA 17.5 21.5 21.9 4.8 3.0 10 19.8 ± 1.9 certified valueCis-Nonachlor 43.2 48.8 41.3 53.8 52.1 45.8 62.1 54.5 NA 46.8 NA 57.7 45.4 50.1 6.4 3.8 11 48.7 ± 7.6 certified valueTrans-Nonachlor 174 160 172 203 174 231 195 213 NA 115 NA 161 228 184 34 20 11 231 ± 11 certified valueDieldrin 53.1 59.2 43.4 38.3 37.8 42.9 NA 58.1 NA 40.0 NA 55.9 NA 47.6 8.8 5.8 9 37.5 ± 3.9 reference valueMirex 27.3 30.1 32.3 22.7 11.8 28.7 NA NA NA 33.2 NA 52.5 20.3 28.8 11 7.3 9 18.9 ± 2.8 certified valueLipid (reported as %) 70.8 68.9 64.3 72.9 77.5 75.9 75.7 73.0 74 69.2 73.0 81.3 74.3 73.1 4.3 2.3 13 74.3 ± 0.45 certified valueOutliers are in bold; not used to calculate the consensus value

Target

Value

Table 6.1: Organochlorine pesticides in SRM 1945 (ng/g wet mass) reported by the participants in the NIST/NOAA Interlaboratory Comparison

Exercise Program for Organic Contaminants and Trace Elements in Marine Mammal Tissues.
16

Assignment of z-and p-scores 

Performance Scores: Different programs have different data quality needs. The acceptability of 

the results submitted by a laboratory will be decided by the individual program(s) for which the 

laboratory provides data. Typically, the program will use these exercise results in conjunction 

with the laboratory’s performance in the analysis of certified reference materials and/or control 

materials, and of other quality assurance samples. These exercise results are shown in a number 

of ways in this report to aid in the evaluation of data quality. 

IUPAC guidelines (IUPAC 1997) describe the use of “z-scores” and “p-scores” for assessment 

of accuracy and precision in interlaboratory comparison exercises, such as described in this 

report. These indices assess the difference between the result of the laboratory and the exercise 

assigned value, and can be used, with caution, to compare performance on different analytes and 

on different materials. 

Accuracy Assessment (z-score):

z = bias estimate / performance criterion 

 

or 

 

z = (x - X)/σ

 

where x is the individual laboratory result, X is the “Exercise Assigned Value,” and σ is the 

target value for the standard deviation. As described in the IUPAC guidelines, the choice of σ is 

dependent upon the data quality objective of a particular program. It can be fixed or determined 

by reference to validated methodology (e.g., the calculated σ from the exercise data, see Tables 

3.1-6.1). The fixed performance criterion is more useful in the comparison of a laboratory’s 

performance on different materials, while the use of the actual variation may be more useful 

within a given exercise, for example, if the determination of a particular analyte is more 

problematic than usual. 

The z-scores calculated using both approaches and applied to each laboratory’s data are given in 

Appendix A. The same criterion was adopted for use in this exercise as was used in the former 

NIST/NOAA/NS&T program, where the target standard deviation was set to 25% of the exercise 

assigned value. The z-scores for the Control Material IV represent 25% of the assigned value so 

that Z = +1 is the assigned value plus 25%, Z = -1 is the assigned value minus 25% and so forth. 

From a scientific point of view, IUPAC does not recommend the classification of z-scores, but 

does allow for such classification, e.g.,

⎪z⎪ ≤ 2 Satisfactory 

2 ≤ ⎪z⎪ ≤ 3 Questionable 

⎪z⎪ ≥ 3 Unsatisfactory 
17

The tables in Appendix A summarize the results and performance indices including the number 

of analytes that fall within each category for each laboratory. 

Precision Assessment (p-score):

 p = σlab / σtarget ≈ CVlab/ CVtarget

 

where σlab and σtarget are variance estimates for the individual laboratory and the target variance, 

respectively. The CVlab is the coefficient of variance (or ratio of standard deviation to the mean), 

while the CVtarget is a reasonable value chosen by the participants. During the workshop that 

accompanied this exercise, a CV of 15% was agreed upon, which is the same value used by the 

former NIST/NOAA/NS&T program. Note that the precision that p describes is that which 

occurs within a batch of analyses. Between batch variance is likely larger and was not assessed 

in this exercise. 

Results and Discussion 

Summarized results are shown in Tables 3.1-6.1. The concentration of many organochlorines in 

Control Material IV was considerably higher than in SRM 1945. The consensus value for the 

sum of PCB congeners in Control Material IV (Table 3.1) was 30,050 ng/g wet mass versus 

1,393 ng/g wet mass in SRM 1945 (Table 5.1). Likewise the sum of the organochlorine 

pesticides in Control Material IV was 29,270 ng/g wet mass versus 1,446 ng/g wet mass in SRM 

1945. 4,4’-DDE was present in the highest concentration in both samples with a consensus value 

of 21,141 ng/g wet mass in Control Material IV and certified value of 445 ng/g wet mass in SRM 

1945. The levels observed in Control Material IV, while higher than SRM 1945, are typical of 

other delphinids from the North Atlantic Ocean (Kuehl et al., 1991). Lipid or “total extractable 

organics” 69.5 % ± 2.5 % in Control Material IV (mean ± 95 % confidence interval; Table 4.1) 

and the average value determined by the participants in SRM 1945 was 73.3 % ± 2.3 % relative 

to the certified value of 74.3 % ± 0.45 % (Table 6.1). 

The relative scatter among the laboratories appeared similar for many of the compounds with 

some exceptions. All laboratories, with the exception of Lab 13 had difficulty obtaining the 

certified value for PCB 31 (Appendix B). This was evident by the large scatter in this plot. 

There was also considerable scatter among the laboratories for the values of PCB 31 in the 

Control Material IV. Laboratories also had difficulty agreeing on the value of PCB congener 

201, both for the control material and the SRM. This may be a result of the two nomenclature 

systems used for this PCB congener (Guitart et al., 1993). High biases (most values exceeding 

the certified value) were observed among the values determined in the SRM relative to the 

certified value for the following compounds: PCB 87, PCB 99, PCB 180, PCB 194, PCB 206, 

PCB 209, 4,4’-DDE, and mirex. Low biases (most values below the certified or reference value) 

were observed for PCB 149, PCB 195, HCB, β-HCH, and trans-nonachlor. 

A number of laboratories reported results for analytes in addition to the target compounds 

(Appendix D). Additional analytes that were reported included other PCB congeners (Labs 1, 2, 

9, 10, and 12), coplanar PCBs (Labs 1 and 9), dioxins and furans (Lab 9), tris-(4-chlorophenyl) 
18

methane and methanol (Lab 8), and endosulfan II and nonachlor III (Lab 2). Interestingly, PCB 

169 was found in Control Material IV in relatively high concentrations for a marine mammal 

tissue (e.g., Kuehl et al., 1991 and Berggrena et al., 1999). The concentration of PCB 169 in this 

material was determined to be 1.93 ng/g wet mass ± 0.040 ng/g wet mass by Lab 1 and 1.84 ng/g 

wet mass ± 0.048 ng/g wet mass by Lab 9. The concentration of PCB 169 (mean ± 95 % 

confidence interval) in SRM 1945 was 0.21 ng/g wet mass ± 0.02 ng/g wet mass measured by 

Lab 1 and 0.13 ng/g wet mass to 0.15 ng/g wet mass measured by Lab 9. 

The participants used a variety of different methods to analyze the materials in this exercise 

(Appendix E). Six laboratories used Soxhlet extraction to extract the materials, two used 

pressurized fluid extraction, and the remaining laboratories used other techniques including 

sonication and column elution. Six laboratories performed a pre-separation on the sample 

extracts prior to GC analysis (i.e., fractionation), while seven did not. Most laboratories (n = 8) 

used GC-ECD to quantify organochlorines, while five laboratories used GC-MS. Internal 

standards were used by eight laboratories, while four laboratories used external standards. 

Conclusions 

During the Nashville workshop there was some discussion regarding materials for future 

exercises. Blubber is typically the marine mammal tissue analyzed for organochlorine 

constituents; hence the program will continue to use this matrix. The exercise coordinators plan 

to vary the type of control material used to include other species of interest such as pinnepeds 

and delphinids. NIST is constrained somewhat on the choice of the material as a fairly large 

quantity (≈1 kg) is needed and this amount of material is not available on a routine basis. SRM 

1945 will continue to be the SRM used in this exercise, since it is the only marine mammal tissue 

available with certified and reference values. This material also has had a number of other 

organochlorine compounds measured and reported, such as coplanar PCBs. The timing of the 

2001 exercise will be similar to the 2000 exercise, with sample material distributed to the 

participants in April 2001 and the results due by October 26, 2001. A workshop to discuss the 

results will be held in conjunction with the 2001 SETAC meeting in Baltimore, Maryland, which 

is held from November 11-15, 2001. 
19

PART 2: DESCRIPTION AND RESULTS OF THE 2000 NIST/NOAA 

INTERLABORATORY COMPARISON EXERCISE PROGRAM FOR TRACE 

ELEMENTS IN MARINE MAMMAL TISSUES 

Materials Used in the Exercise 

Two whale liver homogenate materials and candidate SRM 1946 Lake Superior Fish Tissue were 

issued to the participating laboratories. Whale Liver Homogenate I (QC91LH1) was derived 

from liver tissues collected from Pilot whales stranded in 1990 on Cape Cod, MA (Wise et al.,

1993). Similarly, Whale Liver Homogenate II (QC97LH2) was developed from liver tissue 

collected from Beluga whales taken in Alaska native subsistence hunts in 1996 at Point Lay, AK. 

This material served as the unknown for the exercise. Candidate SRM 1946 Lake Superior Fish 

Tissue was derived from the filleted tissue of Lake Trout (Salvelinus namaycush) collected from 

the Apostle Island region of Lake Superior through coordination with the Wisconsin Department 

of Natural Resources. All of the tissues were cryogenically pulverized and homogenized to 

provide powder-like materials as described above. 

Exercise Requirements and Target Analytes 

The seven participating laboratories (Appendix F, Table 1.2) were each sent ≈ 8 g of each of the 

above materials in frozen jars using liquid nitrogen vapor shippers. A letter of instructions for 

the exercise was included in the shipment along with a reprint of the manuscript containing NIST 

values for the exercise control material (QC91LH1) derived from instrumental neutron activation 

measurements (Wise et al., 1993). Each laboratory submitted data by email using a standard 

data template. 

The following requirements were stipulated to the participants:

1. Analyze samples for core (Cd, Cu, Hg, Fe, Pb) and optional (Ni, Se, As, Zn, Ag) 

elements using accepted analytical procedures. Provide brief descriptions of sample 

preparation and analysis schemes. 

2. Digest, process, and analyze five subsamples of QC97LH2 

3. Digest, process, and analyze five subsamples of Candidate SRM 1946 

4. Digest, process, and analyze three subsamples of QC91LH1 

Evaluation of the Exercise Results 

Establishment of Consensus Values 

A set of guidelines was used by the NIST exercise coordinator to assign concentration (wet 

mass) values for each element in the “unknown” samples. First, the results for each element 

reported from the individual laboratories were evaluated by comparing their results for the 

QC91LH1 control sample against NIST-published data that were collected in 1991 using 
20

instrumental neutron activation analysis (INAA) and made available to each participating 

laboratory. Periodic reanalysis of this cryogenically stored material continues to show that the 

mass fractions of trace elements remain stable. These original measurements provided a good 

estimate of the concentration and range for each element in the QC91LH1 material, as jar-to-jar 

sample heterogeneity was incorporated into the uncertainty estimate and accuracy was verified 

with concurrent analyses of SRM 1577a Bovine Liver. A laboratory’s result for a particular 

element was used if the difference between the reported mean for the participating laboratory and 

the mean of the INAA data differed by no more than 30 %. This criterion was not enforced for 

Pb as it was later determined that Pb was inhomogeneous in all three of the exercise materials. 

No data were rejected as outliers upon application of this criterion. 

A consensus mean (derived from a “mean of laboratory means” determination) for each element 

in each sample was established once the laboratory means and 95 % confidence intervals were 

computed. The 95 % confidence limits (in subsequent tables) and corresponding error bars (in 

subsequent graphs) are expressed as ± ts/√n. The raw laboratory results and summary statistics 

are tabulated in Appendix G, Table 2.2. The corresponding consensus mean summary statistics 

are located in Table 3.2 in Appendix H. Consensus mean plots for each reported element in the 

unknown samples (QC97LH2 and SRM 1946) are given in Appendix I. The consensus mean 

data was used in conjunction with z-scores to evaluate laboratory performance.

Assignment of z-and p-scores 

A discussion on the assignment of z- and p-scores and their classification categories can be 

found in Part 1 of this report. The performance criteria used for the trace element component of 

the exercise were different than the criteria used in the organic contaminants exercise and are 

discussed subsequently. For the trace elements exercise, z-scores were calculated using a target 

standard deviation (σ) of ± 10 % of the consensus mean. For example, for z = ± 1 or z = ± 2 the 

result would be 10 % or 20 % higher (or lower) than the consensus mean, respectively. Z-scores 

should be used to comment on relative and not absolute concentration accuracy, which is 

considered in the next section. With this caveat, z-scores can be classified into the three 

categories described in Part 1 to assess the performance of each laboratory. Using a “fixed” 

performance criterion offers a way for each laboratory to compare their performance on different 

samples. It should be recognized that any particular laboratory might have a detection limit or 

analytical method deficiency for a particular analyte. For marine mammal analyses, the 

acceptability of a particular laboratory’s results should be judged in the context of the data 

quality needs of a particular program. The z-score results for the QC97LH2 and SRM 1946 

samples are displayed in Appendix J, in both tabular (Table 4.2) and graphical format. 

The external repeatability of each laboratory for individual elements was assessed using a pscore where laboratory repeatability (coefficient of variation) was normalized to an assigned 

target value for the coefficient of variation. The value for CVTarget was fixed at 10 % for the 

trace elements exercise. For example, for p = ± 0.5 or p = 1.2 the laboratory repeatability would 

be 5 % or 12 %, respectively. The p-score results for the QC97LH2 and SRM 1946 samples are 

displayed in Appendix J, in Table 5.2. 
21

Normalization Factors 

Interlaboratory comparability helps each participating laboratory demonstrate method validity, 

but method accuracy cannot necessarily be inferred by comparability alone. Ideally, if the 

exercise includes a relatively large number of participants (e.g., >20), the consensus mean should 

provide an unbiased estimate of the true mean. However, when the number of participating 

laboratories is low, the consensus mean value may be skewed by the results from one or two 

laboratories, making it a less useful benchmark for assessing laboratory performance. As the 

number of participating laboratories, and correspondingly, the number of analytical methods 

increase, biases from multiple independent methods will tend to cancel and the consensus mean 

should provide a more useful benchmark. 

It was difficult to assess method accuracy in this round-robin exercise from the consensus data, 

because of the relatively small number of participating laboratories (n = 7), so normalization 

factors computed from the QC91LH1 control data were employed to test the robustness and 

accuracy of each laboratory’s analytical method as applied to the unknown samples. The 

assumption of method robustness and accuracy was challenged because success or failure in 

determining a suite of elements in a particular sample matrix cannot be assumed if the sample 

matrix changes significantly.

The computation of normalization factors was based on the assumption that the mean of the 

NIST values generated in the Gaithersburg and Charleston laboratories using two independent 

techniques (INAA and standard additions ICPMS) provided a good estimate of the “true” 

concentration values of elements in the control sample. Subsequently, the control data generated 

by each laboratory was normalized to this “true” value as a quotient: 

Normalization factors were computed for each element analyzed in the control material and 

normalized laboratory means for the unknown samples were generated by dividing the original 

laboratory mean by the normalization factor. Thereafter, new consensus mean and standard 

deviation data were generated and compared to the original consensus data. This comparison 

was performed to determine if the standard deviation of the consensus mean would be reduced 

after normalization. If an improvement in the standard deviation occurred, the correction factor 

was warranted, implying that the normalized consensus mean provided a better method accuracy 

benchmark. If the standard deviation of the consensus mean increased after normalization, the 

correction factor was not warranted and normalized data would not provide a useful benchmark 

for method accuracy. Appendix K, Table 6.2 lists the normalization factors computed for the 

element suite analyzed by each participating laboratory and Table 7.2 lists the normalized 

consensus mean and summary statistics, along with the results of the correlation tests for the 

unknown QC97LH2 and SRM 1946 samples. 

Normalization Factor

True Value

=

Lab Mean
22

Error Assessment 

Sources of error in interlaboratory comparison exercises can be assessed with a two-sample 

Youden Plot (Youden, 1959). Figure 2.1 illustrates how a Youden plot can be used to provide 

information on the occurrence of indeterminate (random) and determinate (systematic) errors, if 

the concentrations of the analytes are similar in both samples. Results will tend to group at 

random around the intersection of the consensus means if indeterminate errors are occurring 

(Fig. 2.1a). Determinate errors lead to bias in a measurement technique. Typical sources of 

determinate errors are calibration errors, blank correction errors and analytical method errors 

such as analyte volatility (loss) and contamination. Results will tend to group about a line 

running from the origin through the intersection of the consensus mean if determinate errors are 

occurring. This phenomenon is illustrated in Fig. 2.1b in the lower left and upper right quadrants 

of the Youden plot. Youden plots (Appendix L) were generated for elements analyzed in the 

QC91LH1 and QC97LH2 samples, if more than three laboratories reported results. Ninety-five 

percent confidence regions (± ts/√n) were centered on the intersection of the laboratory means 

and superimposed on the intersection of the consensus means, so that the significance of the 

deviation from the consensus values could be judged. 

Results and Discussion 

The participants used several different methods to analyze the materials in this exercise, 

depending on the element: inductively coupled plasma mass spectrometry (ICPMS), inductively 

coupled plasma optical emission spectroscopy (ICP-OES), flame, furnace and cold-vapor atomic 

absorption spectroscopy (AAS), and instrumental neutron activation analysis (INAA). The NIST 

Figure 2.1. Using Youden plots for error assessment.

Mass Fraction (Control)

Mass Fraction (unknown)

Mass Fraction (Control)

Indeterminate Errors Determinate Errors

Low Control

Low Unknown

High Control

High Unknown

Intersection of 

Consensus Means

95% Confidence 

Region

Lab 5

Lab 1

Lab 3

Lab 4

Lab 6

Lab 2

Lab 4

Lab 1

Lab 3

Lab 6

Lab 2

Lab 5

Lab 7 Lab 7

(a) (b)

Figure 2.1. Using Youden plots for error assessment.

Mass Fraction (Control)

Mass Fraction (unknown)

Mass Fraction (Control)

Indeterminate Errors Determinate Errors

Low Control

Low Unknown

High Control

High Unknown

Intersection of 

Consensus Means

95% Confidence 

Region

Lab 5

Lab 1

Lab 3

Lab 4

Lab 6

Lab 2

Lab 4

Lab 1

Lab 3

Lab 6

Lab 2

Lab 5

Lab 7 Lab 7

(a) (b)
23

laboratory in Charleston, SC used ICPMS and the method of standard additions for all elements 

except Hg, which was determined using cold vapor isotope dilution ICPMS. The Nuclear 

Methods group at NIST performed the INAA analyses. 

Data for the full element suite (Cd, Cu, Hg, Fe, Pb, Ni, Se, As, Zn, and Ag) are reported in 

tabular form in the Appendices, where possible. However, consensus data plots, z-plots, and 

Youden diagrams were only generated for Cd, Cu, Hg, Fe, Pb, Se and As due to an insufficient 

number of reporting laboratories for Ni, Zn, and Ag. Accordingly, the results for Ni, Zn, and Ag 

are of limited value and will not be discussed further. 

z- and p-scores 

The z-plots (Appendix J) for QC97LH2 or SRM 1946 show that subgroups of the exercise 

participants have demonstrated comparability within the ⏐0-2⏐ z-range for most elements 

regardless of the sample, using 10% of the consensus mean as the performance criterion. This zscore range implies that a laboratory in this subgroup can distinguish between two samples when 

their respective analyte concentrations differ from 0% to 40%. It should be expected that the zscores of greater than z = ± 1 should occur with greater frequency for the SRM 1946 sample, as 

the analyte concentrations for certain elements are 1 to 2 orders of magnitude lower than their 

respective levels in the QC97LH2 sample. The frequency of higher p-scores for the SRM 1946 

sample can be rationalized using the same argument. The fact that sample inhomogeneity may 

be a limiting factor when evaluating p-scores (i.e., intralaboratory repeatability) should not be 

ignored. In fact, comparing the large variation in p-scores for Pb with those of other elements 

across the laboratories suggests Pb inhomogeneity in the samples. 

Normalization Procedures 

The z-score method fundamentally cannot address the absolute accuracy of consensus data 

unless a lack of bias in the analytical data that yields the consensus value is verified. Application 

of the normalization procedure to the consensus data provided a means to assess the accuracy of 

the consensus data by linking individual measurements (and methods) from a participating 

laboratory to a “true” value. Ideally, the “true” value would be derived from a NIST SRM, so 

that confidence would be implied and agreed upon by all laboratories. In the absence of this 

situation, the results determined by NIST for the pilot whale liver control sample (QC91LH1) 

using standard additions ICPMS and INAA analysis were combined. The comparison test results 

from the normalization procedure (Appendix K) indicated that the standard deviation of the 

consensus value could be improved for Cu, Hg, Fe, and As in QC97LH2 and Hg, Fe, and As in 

candidate SRM 1946. The normalization procedure did not lower the standard deviation of the 

consensus value for Se in either of the samples or Cu in SRM 1946. This implies that the 

laboratory performance on the control standard was not correlated with the performance on the 

unknown sample, suggesting that the robustness of a particular method used in one or more of 

the laboratories was questionable. For example, this may be related to a method detection limit 

phenomenon for Cu. Referring to Table 6.2 in Appendix K, the “true” concentration of Cu in the 

control material (QC91LH1) is 3.26 mg/kg. In QC97LH2 (Table 7.2), normalization improves 

the consensus standard deviation and yields a normalized consensus value of 12.8 ± 0.853 

mg/kg, compared to an original consensus value of 13.1 ± 1.22 mg/kg in Table 3.2. However, in 
24

SRM 1946, normalization worsens the consensus standard deviation and yields a consensus 

value of 0.450 ± 0.212 mg/kg, compared to an original consensus value of 0.473 ± 0.204 mg/kg 

in Table 3.2. The Cu concentration in SRM 1946 is an order of magnitude lower than the 

concentration of Cu in the control material, so good performance on the control material (a 

normalization factor approaching unity) does not infer similar success for SRM 1946. Similarly, 

the Se results suggest a matrix effect rather than a detection limit phenomenon for Se. 

Youden Diagrams 

Youden plots (Appendix L) for Cd, As and Se indicate the presence of indeterminate errors only. 

The results for As and Se were encouraging because two of the laboratories used ICPMS as the 

analytical procedure, where determinations involving these elements are often problematic. The 

INAA methods used by NIST for Cu (Laboratory 2) seemed to produce a low value for the 

QC91LH1 and QC97LH2 samples that was significantly different from the consensus data, while 

Laboratory 4 produced a high Fe value for the QC91LH1 and QC97LH2 samples. The most 

complete data set was reported for Hg, which indicated random errors for all laboratories with 

the possible exception of Laboratory 5, which produced a low value for the QC91LH1 and 

QC97LH2 samples. Youden plots were not generated for QC91LH1 and SRM 1946 because of 

the large differences in trace element concentration. 

Methylmercury Data 

One of the laboratories reported data for methylmercury in the three materials: QC91LH1 (1.422 

mg/kg ± 0.074 mg/kg, n = 12), QC97LH2 (1.296 mg/kg ± 0.074 mg/kg, n = 22) and SRM 1946 

(0.304 mg/kg ± 0.024 mg/kg, n = 17). The latter data may prove useful for comparison with 

methylmercury data produced by the methods that are used in the value assignment and 

certification process for methylmercury in SRM 1946. 

Conclusions 

Several rounds of the exercise will be required to fully assess the state of the practice of trace 

element measurements in marine mammals. Incorporation of more laboratories will also be 

important, as an increased sample size will serve to improve the analytical results and utility of 

any future exercises. Some of the participants have expressed the desire to incorporate analysis 

of an SRM into the exercise (at the expense of the participant) for the purposes of method 

validation. This and other comments are being considered to improve the QA model for 2001 

and beyond. Increasing participation nationally and internationally, and possibly incorporating a 

NIST SRM into the exercise, will allow for a more robust outlier rejection scheme to be 

employed. This aspect is important to consider so that more informative data can be 

disseminated back to the exercise participants. Increasing laboratory participation will also help 

NIST gain access to more reliable consensus values for the candidate SRM materials that are 

distributed in the exercises, providing a secondary benefit from the QA program. It is projected 

that the 2001 trace elements exercise will have 30 participating laboratories, including 12 

international laboratories. 
25

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