Dietary Supplement Laboratory 

Quality Assurance Program: 

Exercise I Final Report

Melissa M. Phillips

Catherine A. Rimmer

Laura J. Wood

Karen E. Murphy

Thomas W. Vetter

NISTIR 7955
Dietary Supplement Laboratory

Quality Assurance Program:

Exercise F Final Report

Melissa M. Phillips

Catherine A. Rimmer

Laura J. Wood

NISTIR 7955

Dietary Supplement Laboratory 

Quality Assurance Program: 

Exercise I Final Report

Melissa M. Phillips

Catherine A. Rimmer

Laura J. Wood

Karen E. Murphy

Thomas W. Vetter

Chemical Sciences Division

Material Measurement Laboratory

August 2013

U.S. Department of Commerce

Penny Pritzker, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director
ii

TABLE OF CONTENTS

ABSTRACT....................................................................................................................................1

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

OVERVIEW OF DATA TREATMENT AND REPRESENTATION

Statistics...............................................................................................................................2

Individual Data Table ..........................................................................................................3

Summary Data Table ...........................................................................................................4

Graphs..................................................................................................................................4

Data Summary View................................................................................................4

Sample/Control Comparison View..........................................................................5

TRACE NUTRITIONAL ELEMENTS IN FOODS AND SUPPLEMENTS

Study Overview ...................................................................................................................6

Sample Information .............................................................................................................6

Multivitamin/multielement tablets...........................................................................6

Whole egg powder...................................................................................................6

Study Results .......................................................................................................................7

Technical Recommendations...............................................................................................7

Table 1. Individual data table (NIST) for trace nutritional elements in foods and dietary 

supplements..............................................................................................................9

Table 2. Data summary table for chromium in foods and dietary supplements...............10

Table 3. Data summary table for molybdenum in foods and dietary supplements..........11

Table 4. Data summary table for selenium in foods and dietary supplements.................12

Figure 1. Chromium in SRM 3280 Multivitamin/Multielement Tablets (method 

comparison data summary view – digestion method)............................................13

Figure 2. Chromium in whole egg powder (data summary view). ..................................14

Figure 3. Molybdenum in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view). .....................................................................................................................15

Figure 4. Molybdenum in whole egg powder (data summary view). ..............................16

Figure 5. Selenium in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view) ......................................................................................................................17

Figure 6. Selenium in whole egg powder (data summary view) .....................................18

Figure 7. Chromium in whole egg powder and SRM 3280 Multivitamin/Multielement 

Tablets (sample/control comparison view)............................................................19

Figure 8. Molybdenum in whole egg powder and SRM 3280 Multivitamin/Multielement 

Tablets (sample/control comparison view)............................................................20

Figure 9. Selenium in whole egg powder and SRM 3280 Multivitamin/Multielement 

Tablets (sample/control comparison view)............................................................21

TOXIC ELEMENTS (CD) IN FOODS AND SUPPLEMENTS

Study Overview .................................................................................................................22

Sample Information ...........................................................................................................22

Fortified breakfast cereal .......................................................................................22
iii

Calcium dietary supplement ..................................................................................22

Study Results .....................................................................................................................22

Technical Recommendations.............................................................................................23

Table 5. Individual data table (NIST) for cadmium in foods and dietary supplements...25

Table 6. Data summary table for cadmium in foods and dietary supplements. ...............26

Figure 10. Cadmium in SRM 3233 Fortified Breakfast Cereal (method comparison data

summary view – digestion method).......................................................................27

Figure 11. Cadmium in candidate SRM 3532 Calcium Dietary Supplement (method 

comparison data summary view – digestion method)............................................28

Figure 12. Cadmium in 3233 Fortified Breakfast Cereal (method comparison data 

summary view – instrumental method)..................................................................29

Figure 13. Cadmium in candidate SRM 3532 Calcium Dietary Supplement (method 

comparison data summary view – instrumental method). .....................................30

Figure 14. Cadmium in candidate SRM 3532 Calcium Dietary Supplement and SRM 

3233 Fortified Breakfast Cereal (sample/control comparison view).....................31

VITAMIN B5 IN FOODS

Study Overview .................................................................................................................32

Sample Information ...........................................................................................................32

Soy Flour................................................................................................................32

Blueberries.............................................................................................................32

Study Results .....................................................................................................................32

Technical Recommendations.............................................................................................33

Table 7. Individual data table (NIST) for vitamin B5 (pantothenic acid) in foods..........34

Table 8. Data summary table for vitamin B5 (pantothenic acid) in foods. ......................35

Figure 15. Vitamin B5 (pantothenic acid) in SRM 3234 Soy Flour (data summary view)36

Figure 16. Vitamin B5 (pantothenic acid) in SRM 3287 Blueberries (data summary 

view) ......................................................................................................................37

Figure 17. Vitamin B5 (pantothenic acid) in SRM 3234 Soy Flour and SRM 3287 

Blueberries (sample/sample comparison view) .....................................................38

VITAMIN A IN FOODS

Study Overview .................................................................................................................39

Sample Information ...........................................................................................................39

Multivitamin/Multielement Tablets.......................................................................39

Egg powder............................................................................................................39

Study Results .....................................................................................................................39

Technical Recommendations.............................................................................................40

Table 9. Individual data table (NIST) for vitamin A in foods..........................................41

Table 10. Data summary table for retinol in foods. .........................................................42

Table 11. Data summary table for retinyl acetate in foods ..............................................43

Table 12. Data summary table for retinyl palmitate in foods...........................................44

Figure 18. Retinol in SRM 3280 Multivitamin/Multielement Tablet (data summary 

view) ......................................................................................................................45

Figure 19. Retinol in whole egg powder (data summary view).......................................46

Figure 20. Retinyl acetate in SRM 3280 Multivitamin/Multielement Tablets (data 
iv

summary view).......................................................................................................47

Figure 21. Retinol in whole egg powder and SRM 3280 Multivitamin/Multielement 

Tablets (sample/control comparison view)............................................................48

CATECHINS IN GREEN TEA

Study Overview .................................................................................................................49

Sample Information ...........................................................................................................49

Green tea extract ....................................................................................................49

Green tea leaves.....................................................................................................49

Study Results .....................................................................................................................50

Technical Recommendations.............................................................................................50

Table 13. Individual data table (NIST) for catechins in green tea ...................................51

Table 14. Data summary table for catechin in green tea..................................................52

Table 15. Data summary table for epicatechin in green tea .............................................53

Table 16. Data summary table for epicatechin gallate in green tea .................................54

Table 17. Data summary table for epigallocatechin in green tea .....................................55

Table 18. Data summary table for epigallocatechin gallate in green tea .........................56

Table 19. Data summary table for gallocatechin in green tea..........................................57

Table 20. Data summary table for gallocatechin gallate in green tea ..............................58

Table 21. Data summary table for total catechins in green tea ........................................59

Figure 22. Catechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data summary 

view) ......................................................................................................................60

Figure 23. Catechin in SRM 3254 Camellia sinensis (Green Tea) (data summary view)61

Figure 24. Epicatechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view).......................................................................................................62

Figure 25. Epicatechin in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view) ......................................................................................................................63

Figure 26. Epicatechin gallate in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view).......................................................................................................64

Figure 27. Epicatechin gallate in SRM 3254 Camellia sinensis (Green Tea) (data 

summary view).......................................................................................................65

Figure 28. Epigallocatechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view).......................................................................................................66

Figure 29. Epigallocatechin in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view) ......................................................................................................................67

Figure 30. Epigallocatechin gallate in SRM 3255 Camellia sinensis (Green Tea) Extract 

(data summary view)..............................................................................................68

Figure 31. Epigallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) (data 

summary view).......................................................................................................69

Figure 32. Gallocatechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view).......................................................................................................70

Figure 33. Gallocatechin in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view) ......................................................................................................................71

Figure 34. Gallocatechin gallate in SRM 3255 Camellia sinensis (Green Tea) Extract 

(data summary view)..............................................................................................72

Figure 35. Gallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) (data 
v

summary view).......................................................................................................73

Figure 36. Total catechins in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view).......................................................................................................74

Figure 37. Total catechins in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view) ......................................................................................................................75

Figure 38. Catechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 3255 

Camellia sinensis (Green Tea) Extract (sample/control comparison view) ..........76

Figure 39. Epicatechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 

3255 Camellia sinensis (Green Tea) Extract (sample/control comparison view) .77

Figure 40. Epicatechin gallate in SRM 3254 Camellia sinensis (Green Tea) Leaves and 

SRM 3255 Camellia sinensis (Green Tea) Extract (sample/control comparison 

view) ......................................................................................................................78

Figure 41. Epigallocatechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and 

SRM 3255 Camellia sinensis (Green Tea) Extract (sample/control comparison 

view) ......................................................................................................................79

Figure 42. Epigallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) Leaves 

and SRM 3255 Camellia sinensis (Green Tea) Extract (sample/control 

comparison view)...................................................................................................80

Figure 43. Gallocatechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 

3255 Camellia sinensis (Green Tea) Extract (sample/control comparison view) .81

Figure 44. Gallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) Leaves 

and SRM 3255 Camellia sinensis (Green Tea) Extract (sample/control 

comparison view)...................................................................................................82

Figure 45. Total catechins in SRM 3254 Camellia sinensis (Green Tea) Leaves and 

SRM 3255 Camellia sinensis (Green Tea) Extract (sample/control comparison 

view) ......................................................................................................................83
1

ABSTRACT

The NIST Dietary Supplement Laboratory Quality Assurance Program (DSQAP) was 

established in collaboration with the National Institutes of Health (NIH) Office of Dietary 

Supplements (ODS) in 2007 to enable members of the dietary supplements community to 

improve the accuracy of measurements for demonstration of compliance with various 

regulations. Exercise I of this program offered the opportunity for laboratories to assess their inhouse measurements of nutritional elements (Cr, Mo, and Se), contaminants (Cd), water-soluble 

vitamins (pantothenic acid), fat-soluble vitamins (retinol), and catechins in foods and/or

botanical dietary supplement ingredients and finished products.

INTRODUCTION

The dietary supplement industry in the US is booming, with two-thirds of adults considering 

themselves to be supplement users.1

 Consumption of dietary supplements, which includes 

vitamin and mineral supplements, represents an annual US expenditure of more than $25 billion. 

These figures represent an increasing American trend, and as a result, it is critically important 

that both the quality and safety of these products are verified and maintained.

The Dietary Supplement Health and Education Act of 1994 (DSHEA) amended the Food, Drug 

and Cosmetic Act to create the regulatory category called dietary supplements. The DSHEA 

also gave the FDA authority to write current Good Manufacturing Practices (cGMPs) that 

require manufacturers to evaluate the identity, purity, and composition of their ingredients and 

finished products. To enable members of the dietary supplements community to improve the 

accuracy of the measurements required for compliance with these and other regulations, NIST 

established the Dietary Supplement Laboratory Quality Assurance Program (DSQAP) in 

collaboration with the NIH ODS in 2007.

The program offers the opportunity for laboratories to assess their in-house measurements of 

active or marker compounds, nutritional elements, contaminants (toxic elements, pesticides, 

mycotoxins), and fat- and water-soluble vitamins in foods as well as in botanical dietary 

supplement ingredients and finished products. Reports and certificates of participation are 

provided and can be used to demonstrate compliance with the cGMPs. In addition, NIST and the 

DSQAP assist the ODS Analytical Methods and Reference Materials program (AMRM) at the 

NIH in supporting the development and dissemination of analytical tools and reference materials. 

In the future, results from DSQAP exercises could be used by ODS to identify problematic 

matrices and analytes for which an Official Method of Analysis would benefit the dietary 

supplement community.

NIST has experience in the area of quality assurance programs, but the DSQAP takes a unique 

approach. In other NIST quality assurance programs, a set of analytes is measured repeatedly 

over time in the same or similar matrices to demonstrate laboratory performance. In contrast, the 

wide range of matrices and analytes under the “dietary supplement” umbrella means that not 

 1 Walsh, T. (2012) Supplement Usage, Consumer Confidence Remain Steady According to New Annual Survey from 

CRN. Council for Responsible Nutrition, Washington, DC.
2

every laboratory is interested in every sample or analyte. The constantly changing dietary 

supplement market, and the enormous diversity of finished products, makes repeated 

determination of a few target compounds in a single matrix of little use to participants. Instead,

participating laboratories are interested in testing in-house methods on a wide variety of 

challenging, real-world matrices to demonstrate that their performance is comparable to that of 

the community and that their methods provide accurate results. In an area where there are few 

standard methods, the DSQAP offers a unique tool for assessment of the quality of 

measurements, provides feedback about performance, and can assist participants in improving 

laboratory operations.

This report summarizes the results from the ninth exercise of the DSQAP, Exercise I. Eightyfive laboratories responded to the call for participants distributed in October 2012. Samples 

were shipped to participants in December 2012, and results were returned to NIST by March 

2013. This report contains the final data and information to be disseminated to the participants 

in July 2013.

OVERVIEW OF DATA TREATMENT AND REPRESENTATION

Statistics

The individual data table and graphs contain information about the performance of each 

laboratory relative to that of the other participants in this study and relative to a target around the 

expected result (if available). The consensus mean and standard deviation are calculated 

according to the robust algorithm outlined in ISO 13528:2005(E), Annex C.2 The algorithm is 

summarized here in simplified form.

Initial values of the consensus mean, x*, and consensus standard deviation, s*, are estimated as

x* = median of xi (i = 1, 2,...,n)

s* = 1.483 × median of |xi – x*| (i = 1, 2,...,n).

These initial values for x* and s* are updated by first calculating the expanded standard 

deviation, δ, as

δ = 1.5 × s*.

Then each xi is compared to the expanded range and adjusted to xi* as described below to reduce 

the effect of outliers.

If xi < x* – δ, then xi* = x* – δ.

If xi > x* + δ, then xi* = x* + δ.

Otherwise, xi* = xi.

New values of x*, s*, and δ are calculated iteratively until the process converges. Convergence 

is taken as no change from one iteration to the next in the third significant figure of s* and in the 

equivalent digit in x*:
3

x* = ∑ xi n ∗ i=1

n

s* = 1.134 × �∑ �xi

∗−x∗� n

i=1

n−1 .

Individual Data Table

The data in this table is individualized to each participating laboratory and is provided to allow 

participants to directly compare their data to the summary statistics (consensus or community 

data as well as NIST certified, reference, or estimated values). The upper left of the data table 

includes the randomized laboratory code. Tables included in this report are generated using 

NIST data to protect the identity and performance of participants.

Section 1 of the data table contains the laboratory results as reported, including the mean and

standard deviation when multiple values were reported. A blank indicates that NIST does not 

have data on file for that laboratory for a particular analyte or matrix. An empty box for standard 

deviation indicates that only a single value was reported and therefore that value was not 

included in the calculation of the consensus data.2

Also in Section 1 are two Z-scores. The first Z-score, Zcomm, is calculated with respect to the 

community consensus value, using x* and s*:

Zcomm = xi−x∗

s∗ .

The second Z-score, ZNIST, is calculated with respect to the target value (NIST certified, 

reference, or estimated value), using xNIST and U95 (the expanded uncertainty) or sNIST, the 

standard deviation of NIST measurements:

ZNIST = xi−xNIST

U95

or

ZNIST = xi−xNIST

sNIST

.

The significance of the Z-score is as follows:

• |Z| < 2 indicates that the laboratory result is considered to be within the community 

consensus range (for Zcomm) or NIST target range (for ZNIST).

• 2 < |Z| < 3 indicates that the laboratory result is considered to be marginally different 

from the community consensus value (for Zcomm) or NIST target value (for ZNIST).

• |Z| > 3 indicates that the laboratory result is considered to be significantly different from 

the community consensus value (for Zcomm) or NIST target value (for ZNIST).

 2 ISO 13528:2005(E), Statistical methods for use in proficiency testing by interlaboratory comparisons, pp 14-15.
4

Section 2 of the data table contains the community results, including the number of laboratories 

reporting more than a single value for a given analyte1

, the mean value determined for each 

analyte, and a robust estimate of the standard deviation of the reported values.

3

 Consensus 

means and standard deviations are calculated using the laboratory means; if a laboratory reported 

a single value, the reported value is not included.1 Additional information on calculation of the 

consensus mean and standard deviation can be found in the previous section.

Section 3 of the data table contains the target values for each analyte. When possible, the target

value is a certified or reference value determined at NIST. Certified values and the associated

expanded uncertainty (U95) have been determined with two independent analytical methods at 

NIST, by collaborating laboratories, or in some combination. Reference values are assigned 

using NIST values obtained from the average and standard deviation of measurements made 

using a single analytical method. For both certified and reference values, at least six samples 

have been tested and duplicate preparations from the sample package have been included, 

allowing the uncertainty to encompass variability due to inhomogeneity within and between 

packages. For samples in which a NIST certified or reference value is not available, the analytes 

are measured at NIST using an appropriate method. The NIST-assessed value represents the 

mean of at least three replicates. For materials acquired from another proficiency testing 

program, the consensus value and uncertainty from the completed round is used as the target 

range.

Summary Data Table

This data table includes a summary of all reported data for a particular analyte in a particular 

study. Participants can compare the raw data for a single laboratory to data reported by the other 

participating laboratories or to the consensus data. A blank indicates that the laboratory signed 

up and received samples for that particular analyte and matrix, but NIST does not have data on 

file for that laboratory.

Graphs

Data Summary View (Method Comparison Data Summary View)

In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). Data points that are unfilled represent laboratories that only reported a 

single value for that analyte and therefore were not included in the consensus mean. The black 

solid line represents the consensus mean, and the black dotted lines represent the consensus 

variability calculated as one standard deviation about the consensus mean. The gray shaded 

region represents the target zone for “acceptable” performance, which encompasses the NIST 

certified, reference, or estimated value bounded by twice its uncertainty (U95) or standard 

deviation. For the purpose of the DSQAP, a target range spanning twice the uncertainty in the 

NIST value is selected because participants are only asked to make a limited number of 

observations. The size of the y-axis on the data summary view graph represents the consensus 

mean bounded by 2δ. In this view, the relative locations of individual laboratory data and 

consensus zones with respect to the target zone can be compared easily. In most cases, the target 

zone and the consensus zone overlap, which is the expected result. One program goal is to 

reduce the size of the consensus zone and center the consensus zone about the target value. 

 3 ISO 13528:2005(E), Statistical methods for use in proficiency testing by interlaboratory comparisons, Annex C.
5

Analysis of an appropriate reference material as part of a quality control scheme can help to 

identify sources of bias for laboratories reporting results that are significantly different from the 

target zone. In the case in which a method comparison is relevant, different colored data points 

may be used to indicate laboratories that used a specific approach to sample preparation, 

analytical method, or quantitation.

Sample/Control Comparison View (Sample/Sample Comparison View)

In this view, the individual laboratory results for a control (NIST SRM with a certified value) are 

compared to the results for an unknown (another NIST SRM with a more challenging matrix, a 

commercial sample, etc.). The error bars represent the individual laboratory standard deviation. 

The solid red box represents the target zone for the control (x-axis) and unknown sample (yaxis). The dotted blue box represents the consensus zone for the control (x-axis) and the 

unknown sample (y-axis). This view emphasizes trends in the data that may indicate potential 

calibration issues or method biases. One program goal is to identify such calibration or method 

biases and assist participants in improving analytical measurement capabilities. In some cases, 

when two equally challenging materials are provided, the same view (sample/sample 

comparison) can be helpful in identifying commonalities or differences in the analysis of the two 

materials.
6

TRACE NUTRITIONAL ELEMENTS IN FOODS AND SUPPLEMENTS

Study Overview

In this study, participants were provided with one NIST SRM, SRM 3280

Multivitamin/Multielement Tablets, and a powdered whole egg material. Participants were 

asked to use in-house analytical methods to determine the mass fractions of three nutritional 

elements (chromium, molybdenum, and selenium) in each of the matrices and report values on 

an as-received basis.

Sample Information

Multivitamin/multielement tablets. Participants were provided with one packet containing 15 

multivitamin/multielement tablets. The material was produced by blending a vitamin and 

mineral pre-mix with a direct-compression tablet formulation. Intact tablets were heat-sealed 

inside 0.1 mm (4 mil) polyethylene bags, which were then sealed inside Mylar bags. Before use,

participants were instructed to grind all tablets together, mix the resulting powder thoroughly, 

and use a sample size of at least 0.5 g. Participants were asked to store the material at controlled 

room temperature, 10 °C to 30 °C, prepare three samples, and report three values from the 

resulting ground material. Approximate analyte levels were not provided to participants prior to 

the study. NIST certified values in SRM 3280 were determined using inductively coupled 

plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry 

(ICP-OES), instrumental neutron activation analysis (INAA), and X-ray florescence 

spectroscopy (XRF). The certified values and uncertainties for Cr, Mo, and Se in SRM 3280 are 

outlined in the table below, both on a dry-mass basis and an as-received basis following 

adjustment for the moisture content of the material (1.37 %).

Certified Mass Fraction (mg/kg) Adjusted Mass Fraction (μg/g)

Analyte (dry-mass basis) (as-received basis)

Cr 93.7 ± 2.7 92.4 ± 2.7

Mo 70.7 ± 4.5 69.7 ± 4.4

Se 17.42 ± 0.45 17.2 ± 0.4

Whole egg powder. Participants were provided with one packet containing approximately 10 g 

of commercially available whole egg powder. The whole egg powder is a free-flowing, fine 

powder prepared from USDA-inspected eggs. The powder was heat-sealed inside nitrogenflushed 0.1 mm (4 mil) polyethylene bags, which were then sealed inside aluminized plastic 

bags. Before use, participants were instructed to thoroughly mix the contents of the packet and 

use a sample size of at least 0.5 g. Participants were asked to store the material at controlled 

room temperature, 10 °C to 30 °C and report three values from the single packet provided. 

Approximate analyte levels were not provided prior to the study. NIST reported values for Cr, 

Mo, and Se using microwave digestion and inductively coupled plasma mass spectrometry (ICPMS) with standard additions as the method of quantitation. The NIST values in whole egg 

powder are reported in the table below with an estimated relative uncertainty of 5 %.
7

Estimated Mass Fraction (mg/kg)

Analyte (as-received basis)

Cr 0.687 ± 0.034

Mo 0.581 ± 0.029

Se 1.40 ± 0.07

Study Results

• Fifty-three laboratories enrolled in this exercise and received samples with a minimum of 

37 laboratories reporting results for one or more elements (70 % participation). 

• The consensus means for chromium and molybdenum in the multivitamin/multielement 

tablets were within the target range with an acceptable variability (14 % and 16 % 

relative standard deviation (RSD), respectively). The consensus mean for selenium in the 

multivitamin/multielement tablets was below the target range, with a slightly higher

variability (19 % RSD). 

• The consensus means for molybdenum and selenium in the whole egg powder were

within the target range. While molybdenum had an acceptable variability (14 % RSD), 

the variability for selenium was higher (26 % RSD). The consensus mean for chromium

in the whole egg powder was above the target range with an unacceptable variability of 

63 % RSD.

• A majority of the laboratories reported using either open-beaker digestion (29 % to 36 %, 

depending on the element) or microwave digestion (52 % to 58 %) for sample 

preparation. The remaining laboratories reported using hot block digestion (11% to 13

%). 

• A majority of the laboratories reported using either ICP-MS (72 % to 81 %, depending on 

the element) or ICP-OES (18 % to 23 %) as their analytical method. Less than 5 % of the 

laboratories reported using atomic absorption spectroscopy (AAS) or total reflection Xray fluorescence (TXRF). 

Technical Recommendations

The following recommendations are based on results reported by the participants in this study. 

• There did not seem to be a difference in results based on either open-beaker digestions or

microwave digestions for the elements in this study. There also did not appear to be any 

difference in results based on either ICP-OES or ICP-MS analytical methods. (Too few 

results were reported by other methods to identify any trends).

• Laboratories that reported high values for one material and low values for the 

second material for any particular element (see Figure 7, Figure 8, and Figure 9) 

may have more trouble digesting one sample matrix over the other. SRM 3280 

Multivitamin/Multielement Tablets are very difficult to digest, requiring relatively 

high temperatures, regardless of digestion method, to get complete sample 

dissolution. Laboratories using higher temperatures for digestions were more 

consistent at reporting values within consensus or target ranges for all elements. 

• It is important to note that with different sample matrices, there may also be 

different interferences to take into consideration during sample analysis.

• The elongated consensus box in Figure 7 is due to several high values reported for the 

whole egg powder. There are several possibilities for this, one being calibration errors. 
8

• The concentrations of these three elements in whole egg powder was 

approximately 10 to 100 times less than those in SRM 3280 

Multivitamin/Multielement Tablets so there was the possibility of contamination 

if the two materials were prepared together. 

• With both ICP-OES and ICP-MS, it is important to check the calibration curve for 

linearity within the range of the sample solutions.

• With ICP-OES, some elements will not be linear beyond an upper limit. Make sure 

solution concentrations fall within that linear range. 

• With ICP-MS, many instruments run in pulse mode, which is more sensitive. If the 

calibration curve extends beyond the dynamic range for pulse mode then the instrument 

will use both the pulse and analog mode. The ICP-MS must be calibrated for both modes 

in this case. It is often easier and more accurate to have a narrower range of calibration 

points, making sure the calibration curve is linear in the pulse mode.

• Run a quality control sample of known accuracy to ensure your method is performing as 

expected.

• Double-check all calculations for any errors.
9

Table 1. Individual data table (NIST) for trace nutritional elements in foods and dietary supplements.

National Institute of Standards & Technology

Exercise I – October 2012 – Nutritional Elements

Lab Code: NIST 1. Your Results 2. Community Results 3. Target

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U95

Cr Multivitamin Tablet μg/g 92.4 2.7 0.2 0.0 41 89.8 12.7 92.4 2.7

Cr Egg Powder μg/g 0.687 0.034 -0.2 0.0 38 0.808 0.511 0.687 0.034

Mo Multivitamin Tablet μg/g 69.7 4.4 -0.1 0.0 39 70.4 11.2 69.7 4.4

Mo Egg Powder μg/g 0.581 0.029 0.0 0.0 35 0.580 0.083 0.581 0.029

Se Multivitamin Tablet μg/g 17.2 0.4 0.4 0.0 39 16.1 3.0 17.2 0.4

Se Egg Powder μg/g 1.40 0.07 -0.1 0.0 36 1.44 0.38 1.40 0.07

xi Mean of reported values N Number of quantitative

values reported

xNIST NIST-assessed value

si Standard deviation of reported 

values

x* Robust mean of reported

values

U95 ±95% confidence 

interval about the 

assessed value or

standard deviation 

(sNIST)

Zcomm Z-score with respect to community 

consensus

s* Robust standard deviation

ZNIST Z-score with respect to NIST value
10

Table 2. Data summary table for chromium in foods and dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 92.4 2.7 0.687 0.034

I901 70.3 65.1 67.6 67.7 2.6 0.610 0.560 0.640 0.603 0.040

I903 99.5 97.6 98.2 98.4 1.0 0.536 0.527 0.528 0.530 0.005

I904

I906

I907

I908 92.5 89.2 88.7 90.1 2.1 0.451 0.444 0.454 0.450 0.005

I910 92.4 101.0 97.9 97.1 4.4 1.060 1.190 1.220 1.157 0.085

I911 89.9 90.4 93.7 91.3 2.1 0.450 0.410 0.440 0.433 0.021

I915

I917 89.5 88.2 89.7 89.1 0.8 1.318 1.368 1.414 1.367 0.048

I920 111.5 110.8 113.0 111.8 1.1 0.660 0.656 0.650 0.655 0.005

I925 77.3 84.0 92.6 84.7 7.7 1.280 1.372 1.789 1.480 0.271

I928 82.1 76.8 80.8 79.9 2.8 1.200 1.100 1.200 1.167 0.058

I930 95.9 108.8 107.3 104.0 7.0 0.518 0.522 0.675 0.572 0.090

I931 77.7 89.5 88.1 85.1 6.4 0.631 0.553 0.520 0.568 0.057

I932 79.3 84.7 85.1 83.0 3.2 0.450 0.450 0.469 0.456 0.011

I933 98.0 99.0 101.0 99.3 1.5

I934 89.5 84.0 92.7 88.7 4.4 8.873 9.132 3.049 7.018 3.439

I935

I936 79.0 77.0 82.0 79.3 2.5 0.430 0.390 0.510 0.443 0.061

I938

I939 72.8 72.8 0.801 0.801

I940 95.3 102.4 86.9 94.9 7.8 1.393 0.557 0.659 0.869 0.456

I941 93.2 92.7 86.2 90.7 3.9 0.418 0.315 0.279 0.337 0.072

I942 80.0 84.0 84.0 82.7 2.3 1.200 1.200 1.200 1.200 0.000

I943 67.4 65.0 70.9 67.8 3.0 0.360 0.350 0.340 0.350 0.010

I944

I947 87.4 108.9 112.9 103.0 13.7 0.432 0.463 0.474 0.456 0.022

I948 81.4 86.6 91.9 86.6 5.3 0.400 0.400 0.400 0.400 0.000

I949 84.8 84.9 80.5 83.4 2.5 1.800 2.000 2.600 2.133 0.416

I950

I951 93.0 88.8 95.1 92.3 3.2 0.434 0.417 0.409 0.420 0.013

I953 89.3 121.8 103.5 104.9 16.3 0.638 0.631 0.683 0.651 0.028

I954 93.9 94.9 87.0 91.9 4.3

I955 95.9 98.2 95.1 96.4 1.6 2.621 3.323 3.612 3.185 0.510

I956 87.7 92.1 94.8 91.5 3.6 2.917 3.646 2.896 3.153 0.427

I958 147.9 151.3 149.2 149.5 1.7 0.200 0.200 0.200 0.200 0.000

I959 91.0 93.0 93.8 92.6 1.5 0.569 0.515 0.601 0.562 0.044

I960 92.9 103.9 98.4 7.8 0.461 0.461 0.425 0.449 0.021

I961 84.1 84.3 80.0 82.8 2.4 0.807 0.775 0.745 0.776 0.031

I963 98.1 92.2 91.9 94.1 3.5

I964 71.9 68.4 70.8 70.4 1.8 0.480 0.520 0.500 0.500 0.020

I965

I966 55.9 56.4 48.6 53.7 4.4 1.600 1.040 1.040 1.227 0.323

I967 101.0 105.0 108.0 104.7 3.5 1.770 1.500 1.800 1.690 0.165

I972 97.1 98.4 98.2 97.9 0.7 0.472 0.505 0.489 0.489 0.017

I973 79.0 81.7 90.2 83.6 5.8 0.465 0.432 0.431 0.443 0.019

I978 62.3 70.3 69.5 67.4 4.4 0.518 0.484 0.589 0.530 0.054

I980 108.0 95.0 97.9 100.3 6.8 0.795 0.683 0.730 0.736 0.056

I981 82.9 76.3 79.8 79.6 3.3 2.280 2.650 2.280 2.403 0.214

I983 108.0 105.0 106.5 2.1

I985 71.7 71.7 0.780 0.780

I986 0.673 0.714 0.674 0.687 0.023

 Consensus Mean 89.8 Consensus Mean 0.808

 Consensus Standard Deviation 12.7 Consensus Standard Deviation 0.511

 Maximum 149.5 Maximum 7.018

 Minimum 53.7 Minimum 0.200

 N 41 N 38

Chromium

SRM 3280 Multivitamin Tablet (μg/g) Whole Egg Powder (μg/g)

Community 

Results Individual Results
11

Table 3. Data summary table for molybdenum in foods and dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 69.7 4.4 0.581 0.029

I901

I903 71.3 68.7 66.3 68.8 2.5 0.615 0.598 0.608 0.607 0.009

I904

I906

I907

I908 86.5 71.5 84.4 80.8 8.1 0.716 0.495 0.440 0.550 0.146

I910 65.0 62.5 70.2 65.9 3.9 1.090 0.632 0.511 0.744 0.305

I911 66.7 65.6 63.2 65.2 1.8 0.556 0.522 0.554 0.544 0.019

I915

I917 72.8 72.3 70.6 71.9 1.1 0.581 0.582 0.591 0.585 0.006

I920 76.7 62.1 69.3 69.3 7.3 0.606 0.622 0.600 0.609 0.011

I925 64.9 69.9 74.5 69.8 4.8 1.386 1.352 1.756 1.498 0.224

I928 89.1 81.7 83.8 84.9 3.8 0.500 0.500 0.500 0.500 0.000

I930 55.4 58.2 56.1 56.6 1.4 0.531 0.523 0.492 0.515 0.021

I931 78.7 67.6 75.6 74.0 5.7 0.578 0.570 0.575 0.574 0.004

I932 94.2 108.4 108.7 103.8 8.3 0.640 0.640 0.633 0.638 0.004

I933 70.0 74.0 72.0 72.0 2.0

I934 66.6 55.7 64.9 62.4 5.9 0.678 0.747 0.598 0.674 0.074

I935

I936 86.0 73.0 74.0 77.7 7.2 0.570 0.550 0.560 0.560 0.010

I938

I939 52.8 52.8 0.361 0.361

I940 74.4 110.1 70.5 85.0 21.8 0.774 0.604 0.540 0.639 0.121

I941 61.7 61.9 62.6 62.1 0.5 0.186 0.159 0.146 0.164 0.021

I942 61.0 65.0 68.0 64.7 3.5 0.550 0.550 0.530 0.543 0.012

I943 65.5 65.2 67.8 66.2 1.4 0.520 0.520 0.510 0.517 0.006

I944

I947 76.2 80.7 78.3 78.4 2.3 0.544 0.498 0.527 0.523 0.023

I948 71.1 72.4 77.9 73.8 3.6 0.570 0.580 0.580 0.577 0.006

I949 49.5 54.6 53.1 52.4 2.6 0.900 0.500 0.700 0.700 0.200

I950

I951 87.5 81.0 70.4 79.6 8.6 0.695 0.658 0.686 0.680 0.019

I953 88.0 78.8 71.4 79.4 8.3 0.566 0.581 0.585 0.577 0.010

I954 60.0 67.7 60.7 62.8 4.3

I955 72.0 65.6 72.7 70.1 3.9 0.449 0.453 0.447 0.450 0.003

I956 67.0 90.7 56.0 71.2 17.8 0.467 0.472 0.459 0.466 0.007

I958 87.5 84.8 82.2 84.8 2.7

I959 61.5 55.7 55.9 57.7 3.3 0.606 0.579 0.607 0.597 0.016

I960 64.8 87.2 76.0 15.8 0.514 0.548 0.488 0.517 0.030

I961 63.0 62.2 15.0 46.7 27.5 0.798 0.776 0.366 0.647 0.244

I963 76.3 79.8 76.7 77.6 1.9

I964 84.4 86.3 85.8 85.5 1.0 0.600 0.620 0.600 0.607 0.012

I965

I966

I967 70.4 58.5 79.9 69.6 10.7 0.630 0.530 0.630 0.597 0.058

I972 67.5 60.4 71.4 66.4 5.6 0.557 0.559 0.549 0.555 0.005

I973 72.3 82.1 75.1 76.5 5.0 0.515 0.494 0.507 0.505 0.011

I978 47.8 52.3 52.9 51.0 2.8 0.622 0.541 0.698 0.620 0.078

I980 77.0 72.9 80.2 76.7 3.7 0.602 0.613 0.602 0.606 0.006

I981 82.8 70.3 77.8 77.0 6.2 0.820 0.640 0.590 0.683 0.121

I983 53.0 56.0 54.5 2.1

I985 50.1 50.1 0.460 0.460

I986 0.592 0.581 0.571 0.581 0.011

 Consensus Mean 70.4 Consensus Mean 0.580

 Consensus Standard Deviation 11.2 Consensus Standard Deviation 0.083

 Maximum 104 Maximum 1.498

 Minimum 47 Minimum 0.164

 N 39 N 35

Molybdenum

SRM 3280 Multivitamin Tablet (μg/g) Whole Egg Powder (μg/g)

Individual Results Community Results
12

Table 4. Data summary table for selenium in foods and dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 17.2 0.4 1.40 0.07

I901

I903 16.4 15.7 17.0 16.4 0.7 1.39 1.40 1.42 1.40 0.02

I904

I906

I907

I908 18.4 17.9 16.0 17.4 1.3 1.65 1.59 1.57 1.60 0.04

I910 17.7 18.0 16.2 17.3 1.0 0.93 1.50 1.13 1.19 0.29

I911 17.0 14.8 15.6 15.8 1.1 1.60 1.50 1.50 1.53 0.06

I915

I917 14.9 15.1 14.6 14.9 0.2 2.14 2.20 2.06 2.13 0.07

I920 12.7 11.6 11.2 11.8 0.8 1.45 1.49 1.44 1.46 0.03

I925 17.8 17.7 17.5 17.7 0.1 1.40 1.37 1.46 1.41 0.05

I928 24.9 20.6 22.7 22.7 2.2 1.80 1.90 1.90 1.87 0.06

I930 14.0 14.9 13.8 14.2 0.6 1.67 1.53 1.49 1.56 0.09

I931 16.2 15.4 15.7 15.7 0.4 1.74 1.57 1.68 1.66 0.09

I932 11.7 12.2 13.6 12.5 1.0 1.58 1.60 1.48 1.55 0.07

I933

I934 18.7 17.5 18.1 18.1 0.6 1.43 0.95 0.94 1.11 0.28

I935

I936 20.0 18.0 19.0 19.0 1.0 1.50 1.70 1.60 1.60 0.10

I938

I939 8.8 8.8 1.81 1.81

I940 11.0 13.2 12.2 12.1 1.1 0.97 0.09 0.97 0.68 0.51

I941 14.9 15.1 15.2 15.0 0.1 0.73 0.76 0.76 0.75 0.02

I942 15.0 16.0 17.0 16.0 1.0 1.70 1.70 1.60 1.67 0.06

I943 18.6 15.9 16.4 17.0 1.4 1.36 1.40 1.20 1.32 0.11

I944

I947 23.1 22.5 20.7 22.1 1.3 1.47 1.37 1.49 1.44 0.06

I948 16.3 15.5 17.8 16.5 1.2 1.40 1.40 1.40 1.40 0.00

I949 15.3 15.3 14.5 15.0 0.5 1.20 1.00 1.30 1.17 0.15

I950

I951 19.3 15.6 17.5 17.4 1.9 1.44 1.35 1.39 1.39 0.05

I953 6.5 9.3 6.4 7.4 1.6 0.83 0.83 0.82 0.83 0.01

I954 16.2 17.1 15.4 16.2 0.9

I955 17.8 16.3 16.8 17.0 0.8 1.69 1.71 1.70 1.70 0.01

I956 19.5 17.1 17.4 18.0 1.3 1.76 1.82 1.74 1.77 0.04

I958 19.9 19.8 21.1 20.3 0.7 0.90 1.00 1.00 0.97 0.06

I959 13.1 10.3 11.2 11.5 1.4

I960 21.1 19.9 20.5 0.9 1.39 1.44 1.32 1.39 0.06

I961 16.0 15.0 15.4 15.4 0.5

I963 18.8 18.4 17.4 18.2 0.7 2.21 2.23 2.19 2.21 0.02

I964 13.0 15.4 13.2 13.9 1.3

I965

I966 21.3 22.1 19.0 20.8 1.6 0.80 0.48 1.04 0.77 0.28

I967 15.6 20.1 17.1 17.6 2.3 1.86 1.62 1.86 1.78 0.14

I972 19.5 14.5 17.0 17.0 2.5 1.30 1.27 1.43 1.33 0.08

I973 15.7 14.9 15.1 15.2 0.4 1.23 1.31 1.37 1.30 0.07

I978 2.8 2.3 3.2 2.8 0.5 1.00 1.08 1.01 1.03 0.05

I980 14.4 12.4 12.9 13.2 1.0 2.04 1.99 1.98 2.00 0.03

I981 16.9 16.0 14.4 15.8 1.3 1.37 1.41 1.43 1.40 0.03

I983 17.5 16.0 16.0 16.5 0.9 1.40 1.50 1.50 1.47 0.06

I985 9.4 9.4 2.00 2.00

I986 1.43 1.41 1.37 1.40 0.03

 Consensus Mean 16.1 Consensus Mean 1.44

 Consensus Standard Deviation 3.0 Consensus Standard Deviation 0.38

 Maximum 22.7 Maximum 2.21

 Minimum 2.8 Minimum 0.68

 N 39 N 36

Selenium

SRM 3280 Multivitamin Tablet (μg/g) Whole Egg Powder (μg/g)

Individual Results Community Results
13

Figure 1. Chromium in SRM 3280 Multivitamin/Multielement Tablets (method comparison 

data summary view – digestion method). In this view, individual laboratory data are plotted with 

the individual laboratory standard deviation (error bars). Data points that are unfilled represent 

laboratories that only reported a single value for that analyte and therefore were not included in 

the consensus mean. The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
14

Figure 2. Chromium in whole egg powder (data summary view). In this view, individual 

laboratory data are plotted with the individual laboratory standard deviation (error bars). Data 

points that are unfilled represent laboratories that only reported a single value for that analyte 

and therefore were not included in the consensus mean. The black solid line represents the 

consensus mean, and the black dotted lines represent the consensus variability calculated as one 

standard deviation about the consensus mean. The gray shaded region represents the target zone 

for “acceptable” performance, which encompasses the NIST-assessed value bounded by an 

uncertainty of 5 %. The NIST value is the mean of three results determined by ICP-MS.
15

Figure 3. Molybdenum in SRM 3280 Multivitamin/Multielement Tablets (data summary view). 

In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). Data points that are unfilled represent laboratories that only reported a 

single value for that analyte and therefore were not included in the consensus mean. The black 

solid line represents the consensus mean, and the black dotted lines represent the consensus 

variability calculated as one standard deviation about the consensus mean. The gray shaded 

region represents the target zone for “acceptable” performance, which encompasses the NIST 

certified value bounded by twice its uncertainty (U95).
16

Figure 4. Molybdenum in whole egg powder (data summary view). In this view, individual 

laboratory data are plotted with the individual laboratory standard deviation (error bars). Data 

points that are unfilled represent laboratories that only reported a single value for that analyte 

and therefore were not included in the consensus mean. The black solid line represents the 

consensus mean, and the black dotted lines represent the consensus variability calculated as one 

standard deviation about the consensus mean. The gray shaded region represents the target zone 

for “acceptable” performance, which encompasses the NIST-assessed value bounded by an 

uncertainty of 5 %. The NIST value is the mean three of results determined by ICP-MS.
17

Figure 5. Selenium in SRM 3280 Multivitamin/Multielement Tablets (data summary view). In 

this view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). Data points that are unfilled represent laboratories that only reported a single value 

for that analyte and therefore were not included in the consensus mean. The black solid line 

represents the consensus mean, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean. The gray shaded region 

represents the target zone for “acceptable” performance, which encompasses the NIST certified 

value bounded by twice its uncertainty (U95).
18

Figure 6. Selenium in whole egg powder (data summary view). In this view, individual 

laboratory data are plotted with the individual laboratory standard deviation (error bars). Data 

points that are unfilled represent laboratories that only reported a single value for that analyte 

and therefore were not included in the consensus mean. The black solid line represents the 

consensus mean, and the black dotted lines represent the consensus variability calculated as one 

standard deviation about the consensus mean. The gray shaded region represents the target zone 

for “acceptable” performance, which encompasses the NIST-assessed value bounded by an 

uncertainty of 5 %. The NIST value is the mean of three results determined by ICP-MS.
19

Figure 7. Chromium in whole egg powder and SRM 3280 Multivitamin/Multielement Tablets 

(sample/control comparison view). In this view, the individual laboratory results for the control 

(SRM 3280 Multivitamin/Multielement Tablets) with a certified value for the analyte are 

compared to the results for a sample (whole egg powder). The error bars represent the individual 

laboratory standard deviation. The solid red lines represent the target zone for the control (xaxis) and the unknown sample (y-axis). The dotted blue box represents the consensus zone for 

the control (x-axis) and the unknown sample (y-axis). 

I966

I978

I901

I943

I964

I985

I939

I936

I981

I928

I942

I961

I932

I949

I973

I925

I931

I948

I934

I917

I908

I941

I911

I956

I954

I951

I959

I963

I940

I955

I910

I972

I960

I903

I933

I980

I947 I930

0.2

0.4

0.6

0.8

1.0

1.2

1.4

50 60 70 80 90 100 110 120 130

Cr in Whole Egg Powder, μg/g

Cr in SRM 3280 Multivitamin Tablet, μg/g
20

Figure 8. Molybdenum in whole egg powder and SRM 3280 Multivitamin/Multielement

Tablets (sample/control comparison view). In this view, the individual laboratory results for the 

control (SRM 3280 Multivitamin/Multielement Tablets) with a certified value for the analyte are 

compared to the results for a sample (whole egg powder). The error bars represent the individual 

laboratory standard deviation. The solid red lines represent the target zone for the control

(x-axis) and the unknown sample (y-axis). The dotted blue box represents the consensus zone 

for the control (x-axis) and the unknown sample (y-axis). 
21

Figure 9. Selenium in whole egg powder and SRM 3280 Multivitamin/Multielement Tablets 

(sample/control comparison view). In this view, the individual laboratory results for the control 

(SRM 3280 Multivitamin/Multielement Tablets) with a certified value for the analyte are 

compared to the results for a sample (whole egg powder). The error bars represent the individual 

laboratory standard deviation. The solid red lines represent the target zone for the control

(x-axis) and the unknown sample (y-axis). The dotted blue box represents the consensus zone 

for the control (x-axis) and the unknown sample (y-axis). 
22

TOXIC ELEMENTS (Cd) IN FOODS AND SUPPLEMENTS

Study Overview

In this study, participants were provided with two NIST SRMs, SRM 3233 Fortified Breakfast 

Cereal and candidate SRM 3532 Calcium Dietary Supplement. Participants were asked to use 

in-house analytical methods to determine the mass fraction of cadmium (Cd) in each of the 

matrices and report values on an as-received basis.

Sample Information

Fortified breakfast cereal. Participants were provided with one packet containing approximately 

10 g of fortified breakfast cereal. This material is a wheat-based fortified flake cereal that was 

ground to 180 μm, blended, and packaged. Before use, participants were instructed to mix the 

contents of the packet thoroughly and use a sample size of at least 0.5 g. Participants were asked 

to store the material at controlled room temperature, 10 °C to 30 °C, prepare three samples, and 

report three values from the single packet provided. Approximate analyte levels were not 

provided to participants prior to the study. The NIST certified value in SRM 3233 was

determined using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS).

The certified value for Cd in SRM 3233 is (81.9 ± 2.0) ng/g on a dry-mass basis. Following 

adjustment for moisture content of the material of 1.70 %, the as-received target value for Cd in 

SRM 3233 is (80.5 ± 2.0) ng/g.

Calcium dietary supplement. Participants were provided with one packet containing 

approximately 10 g of a powdered calcium dietary supplement. The calcium dietary supplement 

was prepared from commercially purchased calcium tablets that were ground to 180 μm, 

blended, and packaged. Before use, participants were instructed to thoroughly mix the contents 

of the packet and use a sample size of at least 0.5 g. Participants were asked to store the material 

at controlled room temperature, 10 °C to 30 °C, prepare three samples, and report three values

from the single packet provided. Approximate analyte levels were not provided to participants 

prior to the study. The NIST-estimated value for Cd in candidate SRM 3532 was determined by 

ID-ICP-MS. The estimated value, based on the mean and expanded uncertainty of duplicate 

measurements from six packets, is (94.7 ± 1.7) ng/g.

Study Results

• Fifty-three laboratories enrolled in this exercise and received samples, and forty-two 

laboratories reported results for Cd (79 % participation).

• The consensus mean for Cd in the fortified breakfast cereal was within the target range 

with an acceptable variability (11 % RSD).

• The consensus mean for Cd in the calcium dietary supplement was slightly below the 

target range but had acceptable variability (16 % RSD).

• A majority of the laboratories reported using either microwave digestion (62 %) or open 

beaker digestion (29 %) for sample preparation. Four laboratories reported using hot 

block digestion (9 %). 

• A majority of the laboratories (88 %) reported using ICP-MS as their analytical method 

for analysis. Only four laboratories reported using either ICP-OES or AAS for their 

analytical measurements for fortified breakfast cereal and five laboratories reported to 
23

have used either ICP-OES or AAS for their analytical measurements for calcium dietary 

supplement (< 12 %).

Technical Recommendations

The following recommendations are based on results provided by the participants in this study. 

• While twice as many laboratories reported using microwave digestion for sample 

preparation than other methods reported, there did not seem to be a difference in results 

based on the sample preparation method used.

• Cadmium can be difficult to measure by ICP-OES because of low sensitivity. Using 

AAS to measure Cd should not pose any significant problems but sometimes an 

extraction or separation step is included.

• Spectral interferences can make Cd difficult to measure by ICP-MS if there are high 

concentrations of certain elements, mainly Mo, Sn, or Zr, but the calcium dietary 

supplement presents the special case of having a high ratio of Ca to Cd 4

.

• A scan of the sample beforehand will indicate if there are potential interferences 

in the sample that will need to be addressed.

• There can be interferences with commonly used masses of Cd (111Cd, 112Cd, 

113Cd, and114

Cd). Examples of molecular interferences include:95, 96, 97 and

98Mo16O+

, 94, 95, 96, and 97Mo16O1H+, 96Zr16O+, 94 and 96Zr16O1H+, 40Ar2

16O2, 40Ca216O2, 

or 40Ca2

16O21

H+; examples of elemental isobaric interferences include: 112Sn, 

113In, and 114Sn. 

• Chemical separations by anion chromatography can reduce interferences but 

because of the labor intensive work involved it is usually impractical for 

laboratories to do a chemical separation on each sample. 

• Collision cell technology, available on most newer-model ICP-MS instruments, 

can be used to remove many of the molecular interferences that may be found in 

these two materials.

• Interference equations inherent to the software provided on some ICP-MS 

instruments are designed to correct for interferences, and these equations can also 

be applied off-line. Both are less labor-intensive alternatives to chemical 

separations.

• Many ICP-MS instruments run in either pulse mode or analog mode. 

• If sample solutions fall outside of the dynamic range for pulse mode, then the 

instrument will use both the pulse and analog mode. In this case, the ICP-MS 

must be calibrated for both modes.

• It is often easier and more accurate to ensure that the calibrants are linear in the 

pulse mode and that the samples are within this linear range.

• As shown in Figure 14, many laboratories reported either high values for both 

samples or low values for both samples. High values may indicate spectral 

interference or contamination. Low values may indicate matrix-induced signal 

suppression which may be avoided with the use of an internal standard. Dilution 

of sample solutions can also decrease matrix-induced signal suppression as long 

as solutions are not diluted below the detection limit. Additionally, high or low 

 4 Murphy, K.E., Vetter, T.W. (2013) Recognizing and overcoming analytical error in the use of ICP-MS for the 

determination of cadmium in breakfast cereal and dietary supplements. Anal Bioanal Chem 405 4579-4588.
24

results can be an indication of a calibration error. A calibration curve needs to 

tightly bracket expected working solutions and be linear in that region. More 

accurate measurements can be achieved by making sure the sample concentrations 

fall within the middle of the calibration curve. 

• Run a well-documented quality control sample with your unknown samples to ensure 

your method is performing as expected.

• Double-check all calculations for errors. Compare these to your quality assurance 

samples to make sure all calculations have been done correctly.
25

Table 5. Individual data table (NIST) for cadmium in foods and dietary supplements.

National Institute of Standards & Technology

Exercise I – October 2012 – Cd

Lab Code: NIST 1. Your Results 2. Community Results 3. Target

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U95

Cd Breakfast Cereal ng/g 80.5 2.0 -0.7 0.0 39 80.4 9.0 80.5 2.0

Cd Ca Supplement ng/g 94.7 1.7 0.3 0.0 40 90.8 14.8 94.7 1.7

xi Mean of reported values N Number of quantitative

values reported

xNIST NIST-assessed value

si Standard deviation of reported 

values

x* Robust mean of reported

values

U95 ±95% confidence 

interval about the 

assessed value or

standard deviation 

(sNIST)

Zcomm Z-score with respect to community 

consensus

s* Robust standard deviation

ZNIST Z-score with respect to NIST value
26

Table 6. Data summary table for cadmium in foods and dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 80.5 2.0 94.7 1.7

I901

I903 80.4 71.7 77.8 76.6 4.5 83.8 78.2 79.7 80.6 2.9

I904

I906

I907

I908 72.0 70.0 78.0 73.3 4.2 79.5 81.5 84.5 81.8 2.5

I910 65.0 55.5 61.9 60.8 4.8 117.0 104.0 122.0 114.3 9.3

I911 88.0 98.0 86.0 90.7 6.4 98.0 85.0 83.0 88.7 8.1

I915

I917 75.7 79.2 76.7 77.2 1.8 86.9 86.9 86.9 86.9 0.0

I920 108.0 96.0 100.0 101.3 6.1 107.0 114.0 110.0 110.3 3.5

I925 78.4 80.8 79.9 79.7 1.2 95.1 94.5 93.1 94.2 1.0

I928 65.0 70.0 70.0 68.3 2.9 72.0 66.0 72.0 70.0 3.5

I929 144.0 145.0 146.0 145.0 1.0 128.0 129.0 130.0 129.0 1.0

I930 72.2 76.3 74.4 74.3 2.1 87.9 81.0 81.1 83.3 4.0

I931 100.0 107.0 111.0 106.0 5.6 66.5 57.4 59.5 61.1 4.8

I932 81.3 77.1 82.8 80.4 3.0 99.2 96.7 98.7 98.2 1.4

I933 74.0 74.0 72.0 73.3 1.2 84.0 82.0 84.0 83.3 1.2

I934 126.0 97.4 115.6 113.0 14.4 119.2 139.2 103.5 120.6 17.9

I935

I936 80.0 85.0 85.0 83.3 2.9 91.0 100.0 100.0 97.0 5.2

I938

I939 52.0 52.0 58.0 58.0

I940 76.7 84.3 73.2 78.1 5.6 63.1 69.3 99.0 77.1 19.1

I942 77.0 81.0 88.0 82.0 5.6 75.0 74.0 76.0 75.0 1.0

I943 84.0 79.0 81.0 81.3 2.5 96.0 92.0 91.0 93.0 2.6

I944

I945 83.7 84.6 84.4 84.2 0.5 98.1 98.3 94.2 96.8 2.3

I947 89.9 86.3 83.5 86.5 3.2 96.7 99.2 92.6 96.1 3.3

I948 100.0 90.0 90.0 93.3 5.8 110.0 100.0 110.0 106.7 5.8

I949

I950 58.7 58.1 57.6 58.1 0.6 61.5 62.7 63.6 62.6 1.1

I951 83.3 90.8 85.3 86.5 3.9 95.6 93.9 100.1 96.5 3.2

I953 72.0 78.0 74.0 74.7 3.1 91.0 91.0 92.0 91.3 0.6

I954 80.0 84.0 80.0 81.3 2.3 90.0 97.0 91.0 92.7 3.8

I955 73.5 72.4 75.4 73.8 1.5 78.2 81.0 80.5 79.9 1.5

I956 75.2 76.3 76.4 75.9 0.7 78.3 82.0 81.1 80.5 2.0

I958 74.0 80.0 78.0 77.3 3.1 110.0 99.0 124.0 111.0 12.5

I959 80.6 77.7 76.7 78.3 2.0 100.7 95.1 94.1 96.6 3.6

I960 83.3 77.5 85.4 82.1 4.1 86.0 102.3 90.7 93.0 8.4

I961 162.2 127.2 112.4 134.0 25.6 254.9 204.7 211.6 223.7 27.2

I962 74.6 69.7 77.6 74.0 4.0

I963 85.4 85.6 81.4 84.1 2.4 101.3 93.7 96.4 97.2 3.8

I964 72.0 75.0 71.0 72.7 2.1 81.0 81.0 84.0 82.0 1.7

I966

I967 81.4 78.0 78.2 79.2 1.9 98.0 97.8 97.1 97.6 0.5

I972 49.3 48.5 48.6 48.8 0.4 60.2 61.1 73.0 64.8 7.2

I973 77.7 68.8 71.5 72.7 4.6 87.8 80.0 89.3 85.7 5.0

I978 86.0 85.0 87.1 86.0 1.1 94.5 90.0 81.4 88.6 6.7

I979

I980 80.0 79.0 77.0 78.7 1.5 98.0 90.0 92.0 93.3 4.2

I983 73.0 79.0 89.0 80.3 8.1 95.0 92.0 98.0 95.0 3.0

I985 57.0 57.0 62.0 62.0

 Consensus Mean 80.4 Consensus Mean 90.8

 Consensus Standard Deviation 9.0 Consensus Standard Deviation 14.8

 Maximum 145.0 Maximum 223.7

 Minimum 48.8 Minimum 58.0

 N 39 N 40

Cadmium

SRM 3233 Fortified Breakfast Cereal (ng/g) Candidate SRM 3532 Ca Supplement (ng/g)

Individual Results Community Results
27

Figure 10. Cadmium in SRM 3233 Fortified Breakfast Cereal (method comparison data 

summary view – digestion method). In this view, individual laboratory data are plotted with the 

individual laboratory standard deviation (error bars). The color of the data point represents the 

sample preparation (digestion) procedure employed. Data points that are unfilled represent 

laboratories that only reported a single value for that analyte and therefore were not included in 

the consensus mean. The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
28

Figure 11. Cadmium in candidate SRM 3532 Calcium Dietary Supplement (method comparison 

data summary view – digestion method). In this view, individual laboratory data are plotted with 

the individual laboratory standard deviation (error bars). The color of the data point represents 

the sample preparation (digestion) procedure employed. Data points that are unfilled represent 

laboratories that only reported a single value for that analyte and therefore were not included in 

the consensus mean. The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST value determined by ID-ICP-MS, bounded by twice the estimated 

uncertainty observed for six duplicate measurements.
29

Figure 12. Cadmium in 3233 Fortified Breakfast Cereal (method comparison data summary 

view – instrumental method). In this view, individual laboratory data are plotted with the 

individual laboratory standard deviation (error bars). The color of the data point represents the 

instrumental method employed. Data points that are unfilled represent laboratories that only 

reported a single value for that analyte and therefore were not included in the consensus mean. 

The black solid line represents the consensus mean, and the black dotted lines represent the 

consensus variability calculated as one standard deviation about the consensus mean. The gray 

shaded region represents the target zone for “acceptable” performance, which encompasses the 

NIST certified value bounded by twice its uncertainty (U95).
30

Figure 13. Cadmium in candidate SRM 3532 Calcium Dietary Supplement (method comparison 

data summary view – instrumental method). In this view, individual laboratory data are plotted 

with the individual laboratory standard deviation (error bars). The color of the data point 

represents the instrumental method employed. Data points that are unfilled represent 

laboratories that only reported a single value for that analyte and therefore were not included in 

the consensus mean. The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST value determined by ID-ICP-MS, bounded by twice the estimated 

uncertainty observed for six duplicate measurements.
31

Figure 14. Cadmium in candidate SRM 3532 Calcium Dietary Supplement and SRM 3233 

Fortified Breakfast Cereal (sample/control comparison view). In this view, the individual 

laboratory results for the control (SRM 3233 Fortified Breakfast Cereal) with a certified value 

for the analyte are compared to the results for a sample (candidate SRM 3532 Calcium Dietary 

Supplement). The error bars represent the individual laboratory standard deviation. The solid 

red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). The

dotted blue box represents the consensus zone for the control (x-axis) and the unknown sample 

(y-axis).
32

VITAMIN B5 IN FOODS

Study Overview

In this study, participants were provided with two NIST SRMs, SRM 3234 Soy Flour and SRM 

3287 Blueberries, neither of which has been fortified with vitamin B5 (pantothenic acid). 

Participants were asked to use in-house analytical methods to determine the mass fractions of 

vitamin B5 in each of the matrices and report values on an as-received basis. Participants were 

asked to report the vitamin B5 content as pantothenic acid; NIST values are reported as 

pantothenic acid.

Sample Information

Soy Flour. Participants were provided one packet containing approximately 15 g of defatted soy 

flour. The flour was heat-sealed inside 0.1 mm (4 mil) polyethylene bags, which were then 

sealed inside Mylar bags. Before use, participants were instructed to thoroughly mix and 

homogenize the contents of the packet and use a sample size of at least 2 g. Participants were 

asked to store the soy flour at controlled room temperature, 10 °C to 30 °C, prepare three 

samples, and report three values from the single packet provided. Approximate analyte levels 

were not provided to participants in the study. The NIST certified value for pantothenic acid in 

SRM 3234 was determined using acidic solvent extraction followed by ID-LC-MS/MS with 

confirmation using data from external collaborating laboratories. The certified value for

pantothenic acid in SRM 3234 is (11.45 ± 0.12) mg/kg on a dry-mass basis. After adjustment for 

moisture content of the material of 6.13 %, the as-received target value for pantothenic acid in 

SRM 3234 is (10.75 ± 0.11) mg/kg.

Blueberries. Participants were provided with three packets, each containing approximately 5 g 

of freeze-dried, powdered blueberries. The blueberries were blended, aliquotted, and heat-sealed 

inside nitrogen-flushed 0.1 mm (4 mil) polyethylene bags, which were then sealed inside 

nitrogen-flushed aluminized plastic bags along with two packets of silica gel each. Before use, 

participants were instructed to thoroughly mix and homogenize the contents of the packet and

use a sample size of at least 2.5 g. Participants were also notified that this material was packaged 

as a powder, but that over time the powder may become a solid mass. For hardened samples, 

participants were instructed to remove an appropriate test portion using a knife. Participants 

were asked to report a single value from each packet provided and to store the blueberries at 

controlled room temperature, 10 °C to 30 °C. Approximate analyte levels were not provided to 

participants prior to the study. The NIST certified value for pantothenic acid in SRM 3287 was 

determined using acidic solvent extraction followed by ID-LC-MS in combination with data 

from external collaborating laboratories. The certified value of pantothenic acid in SRM 3287 is 

(3.36 ± 0.19) mg/kg. After adjustment for moisture content of the material of 1.41 %, the asreceived target value for pantothenic acid in SRM 3287 is (3.31 ± 0.19) mg/kg.

Study Results

• Thirty-three laboratories enrolled in this exercise and received samples, and thirteen 

laboratories reported results for the soy flour and/or blueberries (39 % participation).

• For both materials, the consensus ranges were very wide. For the soy flour, the 

consensus mean was higher than the NIST target range, while the consensus mean for the 

blueberries was contained within the NIST target range (Figure 15 and Figure 16).
33

• The dispersion of the data could be a result of challenges in completely extracting the 

pantothenic acid from the samples or from chromatographic coelutions.

• In the soy flour, nine of the thirteen laboratories (69 %) reported values that were 

reasonably close to the target range. Three of the remaining four laboratories 

reported values that were significantly higher than the target range (10 times higher 

and almost 300 times higher). This could indicate an interference in the analytical 

method (LC-absorbance with external standard calibration) caused by matrix 

components. When using a low wavelength (205 nm to 210 nm) to detect 

pantothenic acid (a molecule without a strong chromophore), the method will be 

highly susceptible to matrix interferences. More information is needed about the 

analytical methods to draw more conclusions.

• In the blueberries, eight of the eleven laboratories (73 %) reported values that were 

reasonably close to the target range. Two of the remaining three laboratories reported 

values that were significantly higher than the target range (150 to 200 times higher). 

These were the same laboratories that reported high values for the soy flour, 

indicating a potential interference in the analytical method or possibly a calibration 

error.

• One laboratory reported values that were 10 times lower than the target value for the 

soy flour and 35 times lower for the blueberries. This could be the result of ion 

suppression in the MS, as this laboratory reported using LC-MS with an external 

standard calibration approach. For accurate quantitation from matrix-based samples, 

the use of isotope dilution for internal standard calibration is critical.

• In general, the analytical approach used did not correlate with any trend in the data. 

In this case, variability in the data is more likely related to the combination of sample 

preparation, instrumental method, and calibration approach, as any method must be 

careful to account for interferences. A larger data set and more information from 

participants is necessary to draw any strong correlations between method and result.

Technical Recommendations

The following are recommendations based on results provided by the participants in this study. 

• No analytical method was identified as being exceptionally good or problematic. When 

using LC-absorbance for a molecule like pantothenic acid without a chromophore, care 

must be taken to remove matrix interferences. The same is true when using LC-MS, as 

matrix components can cause ion suppression leading to results that are biased low unless 

an isotopically labeled analog is used for internal standard calibration.
34

Table 7. Individual data table (NIST) for vitamin B5 (pantothenic acid) in foods.

National Institute of Standards & Technology

Exercise I – October 2012 – Pantothenic Acid

Lab Code: NIST 1. Your Results 2. Community Results 3. Target

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U95

B5 Soy Flour μg/g 10.7 0.10 2.3 -0.4 13 18.6 15.7 10.7 0.1

B5 Blueberries μg/g 3.31 0.19 -0.1 0.0 11 3.49 3.08 3.31 0.19

xi Mean of reported values N Number of quantitative

values reported

xNIST NIST-assessed value

si Standard deviation of reported 

values

x* Robust mean of reported

values

U95 ±95% confidence 

interval about the 

assessed value or

standard deviation 

(sNIST)

Zcomm Z-score with respect to community 

consensus

s* Robust standard deviation

ZNIST Z-score with respect to NIST value
35

Table 8. Data summary table for vitamin B5 (pantothenic acid) in foods.

Lab A B C Avg SD A B C Avg SD

NIST 10.7 0.1 3.31 0.19

I903 11.1 11.0 10.8 11.0 0.2 4.20 3.90 4.20 4.10 0.17

I905

I907

I910

I911

I914

I916

I919 11.6 12.0 11.8 11.8 0.2 4.61 3.35 4.42 4.13 0.68

I924

I928

I931 13.3 12.5 12.3 12.7 0.5 1.71 1.41 1.48 1.53 0.16

I932 16.1 17.5 19.8 17.8 1.9 1.10 5.06 0.83 2.33 2.37

I933

I935

I936 13.0 13.0 13.0 13.0 0.0 1.20 1.50 1.50 1.40 0.17

I937 210.0 226.0 214.0 216.7 8.3

I938

I940 120.9 133.2 142.3 132.1 10.8 540.17 510.45 462.82 504.48 39.02

I941 12.4 14.6 12.4 13.1 1.2 4.82 5.53 4.87 5.07 0.40

I946

I950

I958

I959 12.2 11.6 11.0 11.6 0.6 2.53 2.37 2.37 2.42 0.09

I961

I963 2904.6 2846.0 2907.4 2886.0 34.7 642.17 656.83 652.90 650.63 7.58

I971

I974

I975

I976

I978 1.1 0.9 1.0 1.0 0.1 0.10 0.10 0.09 0.09 0.01

I979

I980 11.8 11.4 11.6 11.6 0.2 1.30 1.00 1.00 1.10 0.17

I983

 Consensus Mean 14.7 Consensus Mean 3.41

 Consensus Standard Deviation 6.0 Consensus Standard Deviation 2.92

 Maximum 2886.0 Maximum 650.63

 Minimum 1.0 Minimum 0.09

 N 12 N 11

Community 

Results

SRM 3234 Soy Flour (μg/g) SRM 3287 Blueberries (μg/g)

Pantothenic Acid

Individual Results
36

Figure 15. Vitamin B5 (pantothenic acid) in SRM 3234 Soy Flour (data summary view). In this 

view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). The black solid line represents the consensus mean, and the black dotted lines 

represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value determined by ID-LC-MS/MS and external collaborating 

laboratories bounded by twice the uncertainty (U95).
37

Figure 16. Vitamin B5 (pantothenic acid) in SRM 3287 Blueberries (data summary view). In 

this view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). The black solid line represents the consensus mean, and the black dotted lines 

represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value determined by ID-LC-MS and external collaborating 

laboratories bounded by twice the uncertainty (U95).
38

Figure 17. Vitamin B5 (pantothenic acid) in SRM 3234 Soy Flour and SRM 3287 Blueberries 

(sample/sample comparison view). In this view, the individual laboratory results for one sample

(SRM 3287 Blueberries) with a certified value for the analyte are compared to the results for a 

second sample (SRM 3234 Soy Flour). The error bars represent the individual laboratory 

standard deviation. The solid red lines represent the target zone for the control (x-axis) and the 

unknown sample (y-axis). The dotted blue box represents the consensus zone for the control (xaxis) and the unknown sample (y-axis). 
39

VITAMIN A IN FOODS AND SUPPLEMENTS

Study Overview

In this study, participants were provided with SRM 3280 Multivitamin/Multielement Tablets and 

a whole egg powder. Participants were asked to use in-house analytical methods to determine 

the mass fractions of vitamin A (as retinol, retinyl acetate, and retinyl palmitate) in each of the 

matrices and report values on an as-received basis.

Sample Information

Multivitamin/Multielement Tablets. Participants were provided with one bottle containing 30

multivitamin/multielement tablets. Before use, participants were instructed to grind all tablets 

together, mix the resulting powder thoroughly, and use a sample size of at least 0.6 g. 

Participants were asked to store the material at controlled room temperature, 10 °C to 30 °C,

prepare three samples, and report three values from the single bottle provided. Approximate 

analyte levels were not provided to participants prior to the study. The NIST reference values 

and uncertainties for vitamin A in SRM 3280 were determined by LC-MS following solvent 

extraction and are reported in the table below, both on a dry-mass basis and after correction for 

moisture of the material (1.37 %).

Egg powder. Participants were provided with one packet containing approximately 10 g of 

whole egg powder. The material is a free-flowing, fine powder prepared from USDA-inspected 

whole eggs. Before use, participants were instructed to mix thoroughly the contents of the 

packet and use a sample size of at least 1 g. Participants were asked to store the material at 

controlled room temperature, 10 °C to 30 °C, prepare three samples, and report three values from 

the single packet provided. Approximate analyte levels were not provided to participants prior to 

the study, and NIST-assessed values and uncertainties were not determined for the whole egg 

powder.

Study Results

• Thirty-seven laboratories enrolled in this exercise and received samples, and 19

laboratories reported results for at least one of the samples (51 % participation).

• NIST target values are available for retinol equivalents and retinyl acetate in the 

multivitamin sample.

• The consensus mean for retinol and retinyl acetate were within the target range.

• The consensus ranges were acceptable for both compounds in the multivitamin 

sample (19 % for both compounds).

• Two laboratories reported values for retinyl palmitate in the multivitamin sample. 

The value from one laboratory appeared to be a conversion of the measured mass 

fraction of retinyl acetate to retinyl palmitate using the relative molecular masses of 

the compounds.

• NIST target values are not available for retinol in the egg powder sample. The consensus 

range for retinol in the egg powder was quite wide (83 % RSD).

• Ten laboratories (53 %) reported using saponification followed by extraction, while nine

laboratories (47 %) reported using solvent extraction to prepare samples.

• A majority of laboratories (95 %) used LC-absorbance for analysis. One laboratory

reported using spectrophotometry.
40

• All laboratories reported using an external standard approach to calibration.

Technical Recommendations

The following recommendations are based on results provided by the participants in this study.

• It is important to determine that saponification methods are appropriate for a given 

sample. Conditions that are too extreme may result in degradation of the analyte of 

interest and conditions that are too gentle may not fully extract the analyte of interest. 

In future exercises, more survey information from participants will be collected about 

saponification to help aid in making recommendations.

• Always be certain that calibrants match the measured analyte (e.g., do not measure 

retinyl acetate with a retinol calibrant).

• Due to the nature of the calibrant materials, a spectrophotometric determination of 

calibrant concentration is essential for accurate measurements. 
41

Table 9. Individual data table (NIST) for vitamin A in foods and supplements.

National Institute of Standards & Technology

Exercise I – October 2012 – Vitamin A

Lab Code: NIST 1. Your Results 2. Community Results 3. Target

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U95

Retinol Vitamin μg/g 438 45 -0.1 0.0 9 447 85 438 45

Retinol Egg Powder μg/g 9 1.600 1.330

Retinyl Acetate Vitamin μg/g 502 52 0.5 0.0 13 460 88 502 52

Retinyl Acetate Egg Powder μg/g 2 3.570 1.300

Retinyl Palmitate Vitamin μg/g 2 392 464

Retinyl Palmitate Egg Powder μg/g 1

xi Mean of reported values N Number of quantitative

values reported

xNIST NIST-assessed value

si Standard deviation of reported 

values

x* Robust mean of reported

values

U95 ±95% confidence 

interval about the 

assessed value or

standard deviation 

(sNIST)

Zcomm Z-score with respect to community 

consensus

s* Robust standard deviation

ZNIST Z-score with respect to NIST value
42

Table 10. Data summary table for retinol in foods.

Lab A B C Avg SD A B C Avg SD

NIST 438 45

I901 387 410 409 402 13

I903 357 355 338 350 10 0.760 0.721 0.755 0.745 0.021

I905 0.600 0.500 0.400 0.500 0.100

I907

I910

I911

I914

I915

I916

I919 408 444 406 419 21 0.622 0.655 0.675 0.651 0.027

I922

I924 425 408 385 406 20 2.100 1.770 1.250 1.707 0.429

I928

I929 560 543 524 542 18 25.000 28.000 23.000 25.333 2.517

I932

I933

I936

I937 434 451 433 439 10

I938

I940

I946

I949

I950

I958

I959 774 774 726 758 28 3.200 3.000 3.200 3.133 0.115

I961

I963

I965

I971

I974

I975

I977

I978 400 304 409 371 58 2.874 2.001 2.351 2.409 0.439

I979

I980 0.763 0.712 0.810 0.762 0.049

I983

I984

 Consensus Mean 449 Consensus Mean 1.73

 Consensus Standard Deviation 94 Consensus Standard Deviation 1.47

 Maximum 758 Maximum 25.33

 Minimum 350 Minimum 0.50

 N 8 N 8

Community 

Results Individual Results

Retinol

SRM 3280 Multivitamin Tablet (μg/g) Whole Egg Powder (μg/g)
43

Table 11. Data summary table for retinyl acetate in foods.

Lab A B C Avg SD A B C Avg SD

NIST 502 52

I901

I903 472 468 445 462 15

I905 452 486 465 468 17

I907

I910 490 508 512 503 12

I911

I914

I915

I916

I919 468 509 466 481 24

I922

I924

I928 399 413 404 405 7

I929

I932 501 514 505 507 7

I933 1670 1700 1660 1677 21

I936

I937

I938

I940 342 343 343 342 0 5.147 4.202 3.787 4.379 0.697

I946

I949 475 456 453 461 12

I950

I958 700 789 760 750 45

I959

I961

I963 807 751 793 784 29

I965

I971

I974

I975

I977

I978 459 349 469 426 67 3.296 2.294 2.696 2.762 0.504

I979

I980 384 384 357 375 16

I983

I984

 Consensus Mean 493 Consensus Mean 3.57

 Consensus Standard Deviation 120 Consensus Standard Deviation 1.30

 Maximum 1677 Maximum 4.38

 Minimum 342 Minimum 2.76

 N 13 N 2

Retinyl Acetate

SRM 3280 Multivitamin Tablet (μg/g) Whole Egg Powder (μg/g)

Individual Results Community Results
44

Table 12. Data summary table for retinyl palmitate in foods.

Lab A B C Avg SD A B C Avg SD

NIST

I901

I903

I905

I907

I910

I911

I914

I915

I916

I919

I922

I924

I928

I929

I932

I933

I936

I937

I938

I940

I946

I949

I950

I958

I959

I961

I963 85 144 78 102 36

I965

I971

I974

I975

I977

I978 734 558 750 681 107 5.27 3.67 4.31 4.42 0.81

I979

I980

I983

I984

 Consensus Mean 392 Consensus Mean

 Consensus Standard Deviation 464 Consensus Standard Deviation

 Maximum 681 Maximum 4.42

 Minimum 102 Minimum 4.42

 N 2 N 1

Individual Results Community Results

Retinyl Palmitate

SRM 3280 Multivitamin Tablet (μg/g) Whole Egg Powder (μg/g)
45

Figure 18. Retinol in SRM 3280 Multivitamin/Multielement Tablet (data summary view). In 

this view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). Data points that are unfilled represent laboratories that only reported a single value 

for that analyte and therefore were not included in the consensus mean. The black solid line 

represents the consensus mean, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean. The gray shaded region 

represents the target zone for “acceptable” performance, which encompasses the NIST reference

value determined by LC-MS (measured as retinyl acetate, expressed as retinol equivalents)

bounded by twice the uncertainty (U95).
46

Figure 19. Retinol in whole egg powder (data summary view). In this view, individual 

laboratory data are plotted with the individual laboratory standard deviation (error bars). The 

black solid line represents the consensus mean, and the black dotted lines represent the 

consensus variability calculated as one standard deviation about the consensus mean.
47

Figure 20. Retinyl acetate in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST reference value determined by LC-MS bounded by twice the uncertainty 

(U95).
48

Figure 21. Retinol in whole egg powder and SRM 3280 Multivitamin/Multielement Tablets 

(sample/control comparison view). In this view, the individual laboratory results for the control 

(SRM 3280 Multivitamin/Multielement Tablets) with a reference value for the analyte are 

compared to the results for an unknown (whole egg powder). The error bars represent the 

individual laboratory standard deviation. The dotted blue box represents the consensus zone for 

the control (x-axis) and the unknown sample (y-axis). 
49

CATECHINS IN GREEN TEA

Study Overview

In this study, participants were provided with two NIST SRMs, SRM 3255 Camellia sinensis 

(Green Tea) Extract and SRM 3254 Camellia sinensis (Green Tea) Leaves. Participants were 

asked to use in-house analytical methods to determine the mass fractions of seven catechins 

(catechin, epicatechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, 

gallocatechin, and gallocatechin gallate), as well as the total amount of catechins, in each of the 

matrices and report values on an as-received basis.

Sample Information

Green tea extract. Participants were provided with three packets, each containing approximately 

1 g of an extract of green tea extract. The spray-dried extract of green tea leaves was heat-sealed 

inside nitrogen-flushed 0.1 mm (4 mil) polyethylene bags, which were then sealed inside 

aluminized plastic bags with two packets of silica gel. Before use, participants were instructed to 

thoroughly mix the contents of each packet and use a sample size of at least 50 mg. Participants 

were asked to store the extract at controlled room temperature, 10 °C to 30 °C, and report a 

single value from each packet. Approximate analyte levels were not provided to participants 

prior to the study. The NIST certified values in SRM 3255 were determined by LC-UV, LC-MS, 

and data from external collaborating laboratories. The certified values and their associated 

uncertainties, corrected for the moisture content of the material (3.13 %), are provided on an asreceived basis in the table below.

Green tea leaves. Participants were provided with three packets, each containing approximately 

3 g of green tea leaves. The ground green tea leaves were heat-sealed inside nitrogen-flushed 0.1 

mm (4 mil) polyethylene bags, which were then sealed inside aluminized plastic bags with 2 

packets of silica gel. Before use, participants were instructed to thoroughly mix the contents of 

the packet and use a sample size of at least 0.4 g. Participants were asked to store the material at 

controlled room temperature, 10 °C to 30 °C, and report a single value from each packet. 

Approximate analyte levels were not provided to participants prior to the study. The NIST 

certified values in SRM 3254 were determined by LC-UV, LC-MS, and data from external 

collaborating laboratories. The certified values and their associated uncertainties, corrected for 

the moisture content of the material (5.19 %), are provided on an as-received basis in the table 

below.

Certified Mass Fraction Certified Mass Fraction

in SRM 3255 (mg/g) in SRM 3254 (mg/g)

Analyte (as-received basis) (as-received basis)

Catechin 8.88 ± 0.90 0.958 ± 0.389

Epicatechin 45.8 ± 6.5 8.53 ± 1.5

Epicatechin Gallate 97.2 ± 7.6 12.0 ± 1.1

Epigallocatechin 79.2 ± 6.3 23.9 ± 4.3

Epigallocatechin Gallate 409 ± 18 49.3 ± 2.1

Gallocatechin 21.3 ± 1.6 2.28 ± 1.0

Gallocatechin Gallate 37.8 ± 1.9 0.939 ± 0.20

Total Catechins 699 ± 22 97.9 ± 5.2
50

Study Results

• Forty-nine laboratories enrolled in this exercise and received samples, and twenty-eight 

laboratories reported results (57 % participation).

• The consensus means for catechin, epicatechin, epicatechin gallate, and epigallocatechin

gallate in the extract were within the target range, with acceptable consensus ranges (9 % 

to 24 % RSD).

• The consensus mean for epigallocatechin was slightly below the target range, while the 

consensus means for gallocatechin and gallocatechin gallate were slightly above the 

target range. The consensus ranges were quite wide for all three (25 % to 72 % RSD).

• The consensus means for catechin, epicatechin, epicatechin gallate, epigallocatechin, and 

epigallocatechin gallate in the ground tea leaves were within the target range, with 

acceptable consensus ranges for epicatechin, epicatechin gallate, and epigallocatechin 

gallate (21 % to 23 % RSD). The consensus ranges for catechin and epigallocatechin 

were significantly wider (67 % RSD and 59 % RSD, respectively).

• The consensus means for gallocatechin and gallocatechin gallate were higher than the 

target range with wide consensus ranges (65 % to 112 % RSD).

• The consensus means for total catechins in both the extract and the leaves were within the 

target range, with acceptable consensus ranges (11 % and 24 % RSD, respectively).

• Laboratories that reported low values typically reported low values for all of the analytes 

in both matrices. The same is true for those laboratories reporting high values.

• Twenty-seven (96 %) of the laboratories reported using solvent extraction followed by 

LC-absorbance with external standard calibration. One laboratory reported using solvent 

extraction with LC-MS and external standard calibration.

• This study was previously conducted in Exercise E of the DSQAP (2010). The results for 

this study are significantly improved, with twice as many laboratories participating and 

more consistent results for nearly all of the individual catechins.

Technical Recommendations

The following recommendations are based on results provided by the participants in this study. 

• Some laboratories (those reporting all high or low values) may have a calibration or 

sample preparation issue. Calibrant materials should be subjected to the same 

preparation procedure as the samples (derivatization, hydrolysis, etc.), and individual 

calibration standards should be used for each compound to improve accuracy. 

• When sample preparation is extensive, an internal standard approach may be required to 

improve accuracy and precision.

• If an internal standard approach is used, it is best to add the internal standard at the 

earliest possible point (i.e. prior to extraction, saponification, and/or derivatization).
51

Table 13. Individual data table (NIST) for catechins in green tea.

National Institute of Standards & Technology

Exercise I – October 2012 – Catechins

Lab Code: NIST 1. Your Results 2. Community Results 3. Target

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U95

Catechin Extract mg/g 8.88 0.90 -0.4 0.0 24 9.84 2.37 8.88 0.90

Catechin Tea mg/g 0.958 0.389 -0.6 0.0 20 1.54 1.04 0.958 0.389

Epicatechin Extract mg/g 45.8 6.5 0.5 0.0 26 43.2 5.8 45.8 6.5

Epicatechin Tea mg/g 8.53 1.52 0.6 0.0 25 7.57 1.6 8.53 1.5

Epicatechin Gallate Extract mg/g 97.2 7.6 0.2 0.0 25 95.1 13.4 97.2 7.6

Epicatechin Gallate Tea mg/g 12.0 1.1 0.0 0.0 24 11.9 2.7 12.0 1.1

Epigallocatechin Extract mg/g 79.2 6.3 0.5 0.0 24 62.9 34.8 79.2 6.3

Epigallocatechin Tea mg/g 23.9 4.3 0.3 0.0 23 20.6 12.2 23.9 4.3

Epigallocatechin Gallate Extract mg/g 409 18 0.0 0.0 28 408 39 409 18

Epigallocatechin Gallate Tea mg/g 49.3 2.1 0.1 0.0 27 48.4 10.6 49.3 2.1

Gallocatechin Extract mg/g 21.3 1.6 -0.3 0.0 17 28.0 20.2 21.3 1.6

Gallocatechin Tea mg/g 2.28 1.04 -0.6 0.0 17 6.66 7.5 2.28 1.0

Gallocatechin Gallate Extract mg/g 37.8 1.9 -0.5 0.0 22 43.1 10.6 37.8 1.9

Gallocatechin Gallate Tea mg/g 0.939 0.199 -0.5 0.0 19 1.380 0.90 0.939 0.20

Total Catechins Extract mg/g 699 22 0.1 0.0 24 691 73 699 22

Total Catechins Tea mg/g 97.9 5.2 0.0 0.0 23 98.0 23.3 97.9 5.2

xi Mean of reported values N Number of quantitative

values reported

xNIST NIST-assessed value

si Standard deviation of reported 

values

x* Robust mean of reported

values

U95 ±95% confidence 

interval about the 

assessed value or

standard deviation 

(sNIST)

Zcomm Z-score with respect to community 

consensus

s* Robust standard deviation

ZNIST Z-score with respect to NIST value
52

Table 14. Data summary table for catechin in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 8.88 0.90 0.958 0.389

I901

I902 11.80 11.50 11.70 11.67 0.15 0.970 1.140 1.000 1.037 0.091

I903 8.48 8.42 8.61 8.50 0.10 0.886 0.905 0.911 0.901 0.013

I904

I905 10.30 10.20 10.20 10.23 0.06 1.700 1.700 1.700 1.700 0.000

I906

I907

I909 4.71 5.10 5.22 5.01 0.27 0.201 0.205 0.188 0.198 0.009

I911

I912 12.40 12.40 12.20 12.33 0.12 2.170 2.130 2.110 2.137 0.031

I913 0.23 0.18 0.25 0.22 0.04

I914

I916

I918 10.09 10.45 10.43 10.32 0.20 1.159 1.037 0.968 1.055 0.097

I921

I922

I923 8.73 8.81 8.77 8.77 0.04 0.780 0.870 0.770 0.807 0.055

I926 12.20 12.30 12.60 12.37 0.21

I927 12.60 12.90 12.73 12.75 0.15 0.894 1.154 1.262 1.104 0.189

I928

I930

I933 141.63 141.30 140.54 141.16 0.56 62.380 62.900 62.740 62.673 0.266

I934 10.20 10.09 10.28 10.19 0.10 1.964 2.676 15.283 6.641 7.493

I938

I939 10.23 10.12 10.07 10.14 0.08 2.816 2.772 2.863 2.817 0.045

I940

I943 10.76 10.88 11.06 10.90 0.15 1.962 1.857 1.849 1.890 0.063

I944

I946 10.70 10.59 10.61 10.63 0.06 0.907 0.907 0.914 0.909 0.004

I947

I950

I952 9.22 9.32 9.72 9.42 0.26 1.240 1.180 1.190 1.203 0.032

I953 111.63 113.17 111.07 111.96 1.09 59.450 60.930 62.330 60.903 1.440

I954 4.83 4.73 4.75 4.77 0.05 0.617 0.602 0.624 0.614 0.011

I956

I957

I958

I963 10.18 10.23 10.12 10.18 0.06 2.302 2.326 2.260 2.296 0.033

I964 7.70 7.63 7.76 7.70 0.07 0.530 0.500 0.470 0.500 0.030

I965

I966 8.40 7.80 8.00 8.07 0.31 1.000 1.200 1.100 1.100 0.100

I968

I969

I970

I976

I979

I982 8.03 7.00 7.63 7.55 0.52 0.100 0.100

I984

I985 9.86 10.01 10.02 9.97 0.09 3.031 2.998 3.048 3.026 0.025

 Consensus Mean 9.87 Consensus Mean 1.602

 Consensus Standard Deviation 2.68 Consensus Standard Deviation 1.229

 Maximum 111.96 Maximum 60.903

 Minimum 4.77 Minimum 0.100

 N 11 N 10

Community 

Results

Catechin

Individual Results

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)
53

Table 15. Data summary table for epicatechin in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 45.8 6.5 8.53 1.52

I901

I902 179.0 87.8 179.0 148.6 52.7 77.50 77.70 77.40 77.53 0.15

I903 45.3 45.2 45.5 45.3 0.2 8.60 8.36 8.35 8.44 0.14

I904

I905 47.4 47.3 47.2 47.3 0.1 8.40 8.50 8.30 8.40 0.10

I906

I907

I909 34.3 37.4 41.5 37.7 3.6 7.72 7.40 7.42 7.51 0.18

I911

I912 45.5 45.6 45.1 45.4 0.3 8.21 7.73 7.66 7.87 0.30

I913 2.5 2.0 2.7 2.4 0.4 0.20 0.18 0.20 0.19 0.01

I914

I916

I918 47.1 46.5 46.1 46.6 0.5 8.05 7.74 7.37 7.72 0.34

I921

I922

I923 45.4 47.9 48.3 47.2 1.6 5.86 6.12 5.45 5.81 0.34

I926 33.6 33.9 34.1 33.9 0.3

I927 48.3 48.8 48.3 48.5 0.3 6.01 8.24 8.11 7.45 1.25

I928

I930

I933 46.2 45.6 45.5 45.8 0.4 6.43 6.69 6.54 6.55 0.13

I934 43.5 44.3 43.8 43.9 0.4 6.24 6.07 6.79 6.37 0.37

I938

I939 42.6 42.4 42.3 42.4 0.2 7.35 7.27 7.26 7.29 0.05

I940

I943 43.2 43.8 43.8 43.6 0.4 7.65 7.50 7.50 7.55 0.09

I944

I946 43.9 44.3 44.3 44.2 0.2 7.76 7.77 7.72 7.75 0.02

I947

I950

I952 46.8 47.3 48.4 47.5 0.9 9.14 10.08 10.17 9.80 0.57

I953 22.3 24.4 21.8 22.8 1.4 3.47 4.40 4.29 4.05 0.51

I954 23.7 23.6 23.6 23.6 0.1 4.37 4.44 4.39 4.40 0.04

I956

I957

I958

I963 47.6 48.5 47.1 47.7 0.7 11.29 9.34 11.08 10.57 1.07

I964 40.1 39.7 40.4 40.1 0.4 7.17 6.84 6.71 6.91 0.24

I965

I966 9.7 8.8 8.6 9.0 0.6 8.60 9.50 8.90 9.00 0.46

I968 49.2 49.1 45.7 48.0 2.0 9.70 9.60 9.40 9.57 0.15

I969

I970

I976

I979

I982 42.2 44.1 42.7 43.0 1.0 7.60 8.20 7.30 7.70 0.46

I984

I985 43.0 42.9 43.2 43.1 0.1 7.57 7.58 7.41 7.52 0.10

 Consensus Mean 42.8 Consensus Mean 7.59

 Consensus Standard Deviation 6.4 Consensus Standard Deviation 1.74

 Maximum 48.0 Maximum 10.57

 Minimum 9.0 Minimum 4.05

 N 12 N 12

Epicatechin

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results
54

Table 16. Data summary table for epicatechin gallate in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 97.2 7.6 12.0 1.1

I901

I902 94.5 94.4 95.3 94.7 0.5 12.2 12.6 12.3 12.4 0.2

I903 99.8 99.9 101.0 100.2 0.7 15.6 15.5 15.7 15.6 0.1

I904

I905 98.9 99.5 98.5 99.0 0.5 14.1 14.2 14.2 14.2 0.1

I906

I907

I909 111.3 107.0 116.1 111.4 4.5 12.3 12.8 12.6 12.6 0.2

I911

I912 93.6 93.9 91.0 92.8 1.6 6.8 6.9 6.0 6.6 0.5

I913 20.4 16.3 22.2 19.6 3.0 1.3 1.2 1.3 1.3 0.1

I914

I916

I918 91.6 88.8 88.3 89.6 1.8 13.9 11.8 11.6 12.4 1.3

I921

I922

I923 85.8 85.0 84.8 85.2 0.5 10.4 10.7 9.6 10.2 0.6

I926 81.4 82.3 82.9 82.2 0.8

I927 97.5 104.0 105.9 102.5 4.4 6.9 10.1 10.9 9.3 2.1

I928

I930

I933 108.5 106.2 107.0 107.2 1.1 11.0 11.0 11.0 11.0 0.0

I934 95.9 97.1 96.7 96.6 0.6 12.8 13.3 13.5 13.2 0.4

I938

I939 128.4 128.6 126.6 127.9 1.1 10.5 10.8 10.7 10.6 0.1

I940

I943 90.6 94.1 93.8 92.8 1.9 12.8 12.3 12.2 12.4 0.3

I944

I946 100.8 101.6 101.6 101.3 0.5 10.4 10.5 10.5 10.4 0.1

I947

I950

I952 101.1 102.3 105.4 102.9 2.2 12.5 13.7 15.8 14.0 1.6

I953 88.5 87.6 88.3 88.1 0.5 11.5 12.2 11.9 11.9 0.3

I954 3.3 3.3 3.3 3.3 0.0 0.5 0.5 0.5 0.5 0.0

I956

I957

I958

I963 81.6 81.7 81.0 81.4 0.4 9.9 9.8 9.7 9.8 0.1

I964 100.0 99.1 101.0 100.0 1.0 12.4 11.9 11.7 12.0 0.4

I965

I966 21.7 19.8 18.9 20.1 1.4 16.0 15.9 15.7 15.9 0.2

I968 104.1 101.7 100.6 102.1 1.8 14.9 15.2 15.0 15.0 0.2

I969

I970

I976

I979

I982 85.0 88.3 88.7 87.3 2.0 14.2 14.2 13.4 13.9 0.5

I984

I985 121.4 121.4 122.0 121.6 0.4 11.0 10.5 10.5 10.7 0.3

 Consensus Mean 94.6 Consensus Mean 11.8

 Consensus Standard Deviation 13.8 Consensus Standard Deviation 2.8

 Maximum 127.9 Maximum 15.9

 Minimum 3.3 Minimum 0.5

 N 12 N 12

Epicatechin gallate

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results
55

Table 17. Data summary table for epigallocatechin in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 79.2 6.3 23.9 4.3

I901

I902 88.5 87.8 89.1 88.5 0.7 19.8 20.0 20.3 20.0 0.3

I903 77.3 76.6 77.7 77.2 0.6 27.9 26.5 27.3 27.2 0.7

I904

I905 88.7 88.7 88.3 88.6 0.2 29.0 29.5 29.2 29.2 0.3

I906

I907

I909 78.0 79.9 80.5 79.5 1.3 18.2 20.1 19.8 19.4 1.0

I911

I912 30.1 30.1 29.3 29.8 0.5 4.7 4.6 4.6 4.6 0.1

I913 1.3 1.0 1.4 1.3 0.2 0.2 0.2 0.2 0.2 0.0

I914

I916

I918 68.2 70.0 71.3 69.8 1.6 24.6 22.6 21.3 22.8 1.7

I921

I922

I923 72.7 72.9 70.7 72.1 1.3 18.0 19.1 17.0 18.0 1.0

I926 64.9 64.7 66.0 65.2 0.7

I927 92.4 94.6 93.2 93.4 1.1 19.9 28.9 27.9 25.6 4.9

I928

I930

I933 75.5 75.3 75.8 75.5 0.3 20.2 21.3 20.8 20.8 0.6

I934 79.5 80.9 80.5 80.3 0.7 23.3 25.8 26.3 25.1 1.6

I938

I939 14.0 13.9 13.9 13.9 0.1 4.4 4.4 4.4 4.4 0.0

I940

I943 68.4 70.5 70.4 69.8 1.2 24.6 23.3 22.9 23.6 0.9

I944

I946 74.1 74.9 75.1 74.7 0.5 25.1 25.1 25.0 25.1 0.0

I947

I950

I952 74.6 74.9 77.2 75.6 1.4 26.4 27.6 26.6 26.9 0.7

I953 49.6 51.0 50.3 50.3 0.7 15.5 16.7 16.6 16.2 0.7

I954 15.7 15.6 15.5 15.6 0.1 4.2 4.3 4.3 4.3 0.1

I956

I957

I958

I963 123.1 123.5 126.4 124.3 1.8 36.0 36.2 35.4 35.9 0.4

I964 89.0 88.4 89.8 89.1 0.7 27.2 25.7 25.2 26.0 1.0

I965

I966 2.0 1.8 2.0 1.9 0.1 44.2 43.7 43.5 43.8 0.4

I968 94.7 86.5 83.1 88.1 6.0 38.0 37.2 36.7 37.3 0.7

I969

I970

I976

I979

I982

I984

I985 11.7 11.8 11.8 11.8 0.1 3.8 3.8 3.7 3.8 0.0

 Consensus Mean 63.8 Consensus Mean 20.8

 Consensus Standard Deviation 33.3 Consensus Standard Deviation 12.5

 Maximum 124.3 Maximum 43.8

 Minimum 1.9 Minimum 3.8

 N 11 N 11

Epigallocatechin

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results
56

Table 18. Data summary table for epigallocatechin gallate in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 409 18 49.3 2.1

I901

I902 409 407 408 408 1 43.3 43.6 44.5 43.8 0.6

I903 420 418 422 420 2 58.9 58.1 59.2 58.7 0.6

I904

I905 458 462 457 459 3 59.6 60.1 60.5 60.1 0.5

I906

I907

I909 358 375 394 376 18 65.2 63.5 64.4 64.4 0.8

I911

I912 415 420 409 415 5 31.7 36.5 28.1 32.1 4.2

I913 56 45 60 54 8 2.7 2.6 2.8 2.7 0.1

I914

I916

I918 424 412 410 416 8 51.9 49.1 47.5 49.5 2.2

I921

I922

I923 373 365 365 368 5 35.9 37.7 33.2 35.6 2.3

I926 349 351 354 351 2

I927 402 411 408 407 4 34.2 50.1 50.1 44.8 9.2

I928 428 426 432 429 3 57.3 54.8 56.3 56.1 1.3

I930

I933 404 402 400 402 2 37.1 38.3 37.8 37.7 0.6

I934 409 412 411 411 2 52.5 52.6 53.6 52.9 0.6

I938

I939 462 464 460 462 2 39.5 40.6 40.2 40.1 0.6

I940 437 429 434 434 4 45.5 45.1 46.5 45.7 0.7

I943 395 400 399 398 2 49.0 47.5 46.8 47.8 1.1

I944

I946 402 407 407 405 3 41.9 42.1 42.2 42.1 0.2

I947

I950

I952 404 409 421 411 9 48.7 53.1 58.3 53.4 4.8

I953 356 367 358 360 6 38.0 42.2 42.1 40.8 2.4

I954 438 437 434 436 2 59.5 60.6 59.5 59.9 0.6

I956

I957

I958

I963 408 403 399 403 5 45.6 45.5 45.5 45.5 0.1

I964 436 433 441 437 4 49.2 46.8 46.1 47.4 1.6

I965

I966 89 82 78 83 6 54.6 53.4 51.7 53.2 1.5

I968 406 406 399 404 4 60.2 59.6 58.5 59.4 0.9

I969

I970

I976

I979

I982 449 465 463 459 9 66.3 67.5 62.5 65.4 2.6

I984

I985 463 464 466 464 1 40.3 39.3 38.8 39.4 0.8

 Consensus Mean 409 Consensus Mean 48.3

 Consensus Standard Deviation 39 Consensus Standard Deviation 11.0

 Maximum 464 Maximum 65.4

 Minimum 83 Minimum 39.4

 N 13 N 13

Epigallocatechin gallate

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results
57

Table 19. Data summary table for gallocatechin in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 21.3 1.6 2.28 1.04

I901

I902

I903 12.9 12.6 12.5 12.7 0.2 6.57 6.84 7.15 6.85 0.29

I904

I905 24.3 24.2 24.3 24.3 0.1 4.20 4.10 4.20 4.17 0.06

I906

I907

I909 14.6 17.1 18.8 16.8 2.1 1.13 1.12 1.07 1.10 0.03

I911

I912 99.9 100.1 100.4 100.1 0.3 31.15 29.03 29.11 29.76 1.20

I913 0.1 0.1 0.1 0.0 0.02 0.02 0.02 0.00

I914

I916

I918 5.9 5.7 5.8 5.8 0.1 0.30 0.26 0.29 0.28 0.02

I921

I922

I923 18.1 19.7 19.3 19.0 0.8 1.78 2.17 1.82 1.92 0.21

I926

I927 28.2 29.3 29.1 28.9 0.6 3.14 4.00 4.52 3.89 0.70

I928

I930

I933 113.7 113.2 115.6 114.2 1.2 17.48 17.07 17.61 17.39 0.28

I934 22.6 23.3 22.5 22.8 0.4 2.41 2.43 2.61 2.48 0.11

I938

I939

I940

I943

I944

I946 26.1 26.4 26.4 26.3 0.2 4.08 4.09 4.07 4.08 0.01

I947

I950

I952 22.8 22.9 23.6 23.1 0.5 3.72 5.40 3.66 4.26 0.99

I953 15.4 24.5 22.2 20.7 4.8 6.13 5.86 6.34 6.11 0.24

I954 131.0 131.0 129.0 130.3 1.2 19.40 19.70 19.30 19.47 0.21

I956

I957

I958

I963 28.7 28.9 28.6 28.7 0.2 4.52 4.51 4.46 4.50 0.03

I964

I965

I966

I968 47.9 55.5 45.9 49.8 5.1 27.78 27.36 29.06 28.07 0.89

I969

I970

I976

I979

I982 22.3 23.4 22.9 22.9 0.6 3.30 2.60 2.21 2.70 0.55

I984

I985

 Consensus Mean 26.6 Consensus Mean 5.42

 Consensus Standard Deviation 16.9 Consensus Standard Deviation 4.99

 Maximum 130.3 Maximum 28.07

 Minimum 20.7 Minimum 2.70

 N 7 N 7

Gallocatechin

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results
58

Table 20. Data summary table for gallocatechin gallate in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 37.8 1.9 0.939 0.199

I901

I902 44.8 45.2 46.2 45.4 0.7 1.910 1.840 2.090 1.947 0.129

I903 42.8 42.8 42.9 42.8 0.1 1.260 1.190 1.160 1.203 0.051

I904

I905 1.4 1.4 1.5 1.4 0.1 0.100 0.100 0.100 0.100 0.000

I906

I907

I909 37.7 37.2 49.1 41.3 6.7 1.279 1.303 1.282 1.288 0.013

I911

I912 36.0 36.5 35.2 35.9 0.7

I913 7.0 5.5 7.5 6.7 1.0 0.060 0.060 0.060 0.060 0.000

I914

I916

I918 43.0 42.2 42.1 42.4 0.5 1.129 1.163 1.281 1.191 0.080

I921

I922

I923 41.6 41.2 41.1 41.3 0.3 1.120 1.140 1.030 1.097 0.059

I926 42.2 41.9 42.5 42.2 0.3

I927 101.5 106.1 105.2 104.3 2.5 2.700 2.473 4.277 3.150 0.983

I928

I930

I933 61.2 52.3 52.6 55.4 5.1 1.310 1.380 1.360 1.350 0.036

I934 53.4 54.2 54.1 53.9 0.4 1.205 1.147 1.266 1.206 0.060

I938

I939 39.2 38.6 38.4 38.7 0.4 0.877 0.990 1.044 0.971 0.085

I940

I943

I944

I946 55.3 55.3 55.6 55.4 0.2 1.776 1.795 1.785 1.786 0.010

I947

I950

I952 42.4 42.8 43.9 43.0 0.8 2.060 2.020 2.510 2.197 0.272

I953 15.8 16.9 15.4 16.0 0.8 0.414 0.041 0.381 0.279 0.206

I954 47.2 47.1 46.6 47.0 0.3 1.420 1.440 1.370 1.410 0.036

I956

I957

I958

I963 57.8 55.3 55.0 56.0 1.5 2.616 2.430 2.560 2.535 0.095

I964 41.9 41.7 42.6 42.1 0.5 1.040 1.000 0.950 0.997 0.045

I965

I966

I968 52.7 53.0 49.0 51.6 2.2 4.266 4.268 3.085 3.873 0.682

I969

I970

I976

I979

I982 37.1 37.8 38.4 37.7 0.7 0.800 0.800

I984

I985 35.4 35.7 35.9 35.7 0.2 1.314 1.234 1.116 1.221 0.100

 Consensus Mean 43.1 Consensus Mean 1.342

 Consensus Standard Deviation 10.6 Consensus Standard Deviation 0.847

 Maximum 56.0 Maximum 3.873

 Minimum 16.0 Minimum 0.279

 N 10 N 9

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results

Gallocatechin gallate
59

Table 21. Data summary table for total catechins in green tea.

Lab A B C Avg SD A B C Avg SD

NIST 699 22 97.9 5.2

I901

I902 828 825 829 827 2 155.7 156.9 157.6 156.7 1.0

I903 712 709 715 712 3 120.0 118.0 120.0 119.3 1.2

I904

I905 734 739 732 735 3 117.4 118.5 118.5 118.1 0.6

I906

I907

I909 638 659 705 668 34 106.0 106.4 106.8 106.4 0.4

I911

I912 733 739 722 731 8 84.8 86.8 77.6 83.1 4.8

I913 88 70 94 84 13 4.5 4.2 4.6 4.4 0.2

I914

I916

I918 690 676 674 680 9 101.0 93.6 90.3 95.0 5.5

I921

I922

I923 645 640 638 641 4 73.9 77.8 68.8 73.5 4.5

I926 583 586 592 587 4

I927 783 807 802 797 13 73.7 104.9 107.2 95.3 18.7

I928

I930

I933 951 936 937 941 8 156.0 158.7 157.8 157.5 1.4

I934 714 722 72 503 373 100.5 104.0 105.6 103.3 2.6

I938

I939 696 697 691 695 3 65.5 66.8 66.4 66.2 0.7

I940

I943 608 619 618 615 6 96.0 92.4 91.2 93.2 2.5

I944

I946 713 720 721 718 4 91.9 92.3 92.2 92.1 0.2

I947

I950

I952 701 708 729 713 15 103.7 113.1 118.2 111.7 7.3

I953 663 687 670 673 13 135.2 143.2 144.6 141.0 5.1

I954 664 662 657 661 4 90.0 91.6 90.0 90.5 0.9

I956

I957

I958

I963 753 751 747 750 3 112.2 110.1 109.9 110.7 1.3

I964 715 710 723 716 7 97.5 92.8 91.1 93.8 3.3

I965

I966

I968 755 752 723 743 17 154.9 153.3 151.8 153.3 1.5

I969

I970

I976

I979

I982 649 671 669 663 12 91.4 93.4 85.4 90.1 4.2

I984

I985 684 685 689 686 2 66.9 65.4 64.6 65.7 1.2

 Consensus Mean 694 Consensus Mean 102.0

 Consensus Standard Deviation 73 Consensus Standard Deviation 29.7

 Maximum 750 Maximum 153.3

 Minimum 615 Minimum 65.7

 N 11 N 11

Total catechins

SRM 3255 Green Tea Extract (mg/g) SRM 3254 Green Tea (mg/g)

Individual Results Community Results
60

Figure 22. Catechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data summary view). 

In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
61

Figure 23. Catechin in SRM 3254 Camellia sinensis (Green Tea) (data summary view). In this 

view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). Data points that are unfilled represent laboratories that only reported a single value 

for that analyte and therefore were not included in the consensus mean. The black solid line 

represents the consensus mean, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean. The gray shaded region 

represents the target zone for “acceptable” performance, which encompasses the NIST certified 

value bounded by twice its uncertainty (U95).
62

Figure 24. Epicatechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
63

Figure 25. Epicatechin in SRM 3254 Camellia sinensis (Green Tea) (data summary view). In 

this view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). The black solid line represents the consensus mean, and the black dotted lines 

represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
64

Figure 26. Epicatechin gallate in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view). In this view, individual laboratory data are plotted with the individual 

laboratory standard deviation (error bars). The black solid line represents the consensus mean, 

and the black dotted lines represent the consensus variability calculated as one standard deviation 

about the consensus mean. The gray shaded region represents the target zone for “acceptable” 

performance, which encompasses the NIST certified value bounded by twice its uncertainty 

(U95).
65

Figure 27. Epicatechin gallate in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
66

Figure 28. Epigallocatechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
67

Figure 29. Epigallocatechin in SRM 3254 Camellia sinensis (Green Tea) (data summary view). 

In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
68

Figure 30. Epigallocatechin gallate in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view). In this view, individual laboratory data are plotted with the individual 

laboratory standard deviation (error bars). The black solid line represents the consensus mean, 

and the black dotted lines represent the consensus variability calculated as one standard deviation 

about the consensus mean. The gray shaded region represents the target zone for “acceptable” 

performance, which encompasses the NIST certified value bounded by twice its uncertainty 

(U95).
69

Figure 31. Epigallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
70

Figure 32. Gallocatechin in SRM 3255 Camellia sinensis (Green Tea) Extract (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
71

Figure 33. Gallocatechin in SRM 3254 Camellia sinensis (Green Tea) (data summary view). In 

this view, individual laboratory data are plotted with the individual laboratory standard deviation

(error bars). The black solid line represents the consensus mean, and the black dotted lines 

represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
72

Figure 34. Gallocatechin gallate in SRM 3255 Camellia sinensis (Green Tea) Extract (data 

summary view). In this view, individual laboratory data are plotted with the individual 

laboratory standard deviation (error bars). The black solid line represents the consensus mean, 

and the black dotted lines represent the consensus variability calculated as one standard deviation 

about the consensus mean. The gray shaded region represents the target zone for “acceptable” 

performance, which encompasses the NIST certified value bounded by twice its uncertainty 

(U95).
73

Figure 35. Gallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). Data points that are unfilled represent laboratories that only reported a 

single value for that analyte and therefore were not included in the consensus mean. The black 

solid line represents the consensus mean, and the black dotted lines represent the consensus 

variability calculated as one standard deviation about the consensus mean. The gray shaded 

region represents the target zone for “acceptable” performance, which encompasses the NIST 

certified value bounded by twice its uncertainty (U95).
74

Figure 36. Total catechins in SRM 3255 Camellia sinensis (Green Tea) Extract (data summary 

view). In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
75

Figure 37. Total catechins in SRM 3254 Camellia sinensis (Green Tea) (data summary view). 

In this view, individual laboratory data are plotted with the individual laboratory standard 

deviation (error bars). The black solid line represents the consensus mean, and the black dotted 

lines represent the consensus variability calculated as one standard deviation about the consensus 

mean. The gray shaded region represents the target zone for “acceptable” performance, which 

encompasses the NIST certified value bounded by twice its uncertainty (U95).
76

Figure 38. Catechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 3255

Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis). 
77

Figure 39. Epicatechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 3255 

Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).
78

Figure 40. Epicatechin gallate in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 

3255 Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).
79

Figure 41. Epigallocatechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 

3255 Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).
80

Figure 42. Epigallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) Leaves and 

SRM 3255 Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this 

view, the individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with 

a certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).
81

Figure 43. Gallocatechin in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 3255 

Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).
82

Figure 44. Gallocatechin gallate in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 

3255 Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).
83

Figure 45. Total catechins in SRM 3254 Camellia sinensis (Green Tea) Leaves and SRM 3255 

Camellia sinensis (Green Tea) Extract (sample/control comparison view). In this view, the 

individual laboratory results for the control (SRM 3255 Camellia sinensis Extract) with a 

certified value for the analyte are compared to the results for an unknown (SRM 3254 Camellia 

sinensis Leaves). The error bars represent the individual laboratory standard deviation. The 

solid red lines represent the target zone for the control (x-axis) and the unknown sample (y-axis). 

The dotted blue box represents the consensus zone for the control (x-axis) and the unknown 

sample (y-axis).