Dietary Supplement Laboratory 

Quality Assurance Program: 

Exercise K Final Report

Melissa M. Phillips

Catherine A. Rimmer

Laura J. Wood

This publication is available free of charge 

from: http://dx.doi.org/10.6028/NIST.IR.8032

NISTIR 8032
NISTIR 8032

Dietary Supplement Laboratory 

Quality Assurance Program: 

Exercise K Final Report

Melissa M. Phillips

Catherine A. Rimmer

Laura J. Wood

Chemical Sciences Division

Material Measurement Laboratory

This publication is available free of charge 

from: http://dx.doi.org/10.6028/NIST.IR.8032

November 2014

U.S. Department of Commerce

Penny Pritzker, Secretary

National Institute of Standards and Technology

Willie May, Acting Under Secretary of Commerce for Standards and Technology and Acting Director 
ii

TABLE OF CONTENTS

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

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

OVERVIEW OF DATA TREATMENT AND REPRESENTATION .....................................2

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

Individualized Data Table....................................................................................................3

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

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

Data Summary View (Method Comparison Data Summary View) ........................4

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

NUTRITIONAL ELEMENTS (P, FE) IN CRANBERRY AND BLUEBERRY.....................6

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

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

Cranberry .................................................................................................................6

Blueberry..................................................................................................................6

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

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

Table 1. Individualized data summary table (NIST) for nutritional elements in cranberry 

and blueberry ...........................................................................................................9

Table 2. Data summary table for phosphorus in cranberry and blueberry.......................10

Table 3. Data summary table for iron in cranberry and blueberry...................................11

Figure 1. Phosphorus in SRM 3281 Cranberry (Fruit) (data summary view – digestion

method) ..................................................................................................................12

Figure 2. Phosphorus in SRM 3287 Blueberry (Fruit) (data summary view – digestion

method) ..................................................................................................................13

Figure 3. Iron in SRM 3281 Cranberry (Fruit) (data summary view – digestion method) ...14

Figure 4. Iron in SRM 3287 Blueberry (Fruit) (data summary view – digestion method)

................................................................................................................................15

Figure 5. Phosphorus in SRM 3281 Cranberry (Fruit) (data summary view – instrumental 

method) ..................................................................................................................16

Figure 6. Phosphorus in SRM 3287 Blueberry (Fruit) (data summary view – instrumental 

method) ..................................................................................................................17

Figure 7. Iron in SRM 3281 Cranberry (Fruit) (data summary view – instrumental method)

................................................................................................................................18

Figure 8. Iron in SRM 3287 Blueberry (Fruit) (data summary view – instrumental method)

................................................................................................................................19

Figure 9. Phosphorus in SRM 3287 Blueberry (Fruit) and SRM 3281 Cranberry (Fruit) 

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

Figure 10. Iron in SRM 3287 Blueberry (Fruit) and SRM 3281 Cranberry (Fruit) 

(sample/sample comparison view).........................................................................21
iii

TOXIC ELEMENTS (Hg) IN EPHEDRA AND GINKGO DIETARY SUPPLEMENTS...22

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

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

Ephedra Aerial Parts.............................................................................................22

Ginkgo Leaves........................................................................................................22

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

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

Table 4. Individualized data summary table (NIST) for mercury in Ephedra and Ginkgo 

dietary supplements. ..............................................................................................24

Table 5. Data summary table for mercury in Ephedra and Ginkgo dietary supplements

................................................................................................................................25

Figure 11. Mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts (data summary view 

– digestion method)................................................................................................26

Figure 12. Mercury in SRM 3246 Ginkgo biloba (Leaves) (data summary view – digestion 

method) ..................................................................................................................27

Figure 13. Mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts (data summary view 

– instrumental method) ..........................................................................................28

Figure 14. Mercury in SRM 3246 Ginkgo biloba (Leaves) (data summary view –

instrumental method) .............................................................................................29

Figure 15. Mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts and SRM 3246 

Ginkgo biloba (Leaves) (sample/sample comparison view)..................................30

WATER-SOLUBLE VITAMINS (B1, B2, B3) IN DIETARY SUPPLEMENTS..................31

Study Overview .................................................................................................................31

Sample Information ...........................................................................................................31

Multivitamin/Multielement Tablets.......................................................................31

Protein Powder.......................................................................................................31

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

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

Table 6. Individualized data summary table (NIST) for water-soluble vitamins in dietary 

supplements............................................................................................................34

Table 7. Data summary table for vitamin B1 (thiamine hydrochloride) in dietary 

supplements............................................................................................................35

Table 8. Data summary table for vitamin B2 (riboflavin) in dietary supplements ..........37

Table 9. Data summary table for vitamin B3 (niacinamide) in dietary supplements.......39

Figure 16. Thiamine hydrochloride in SRM 3280 Multivitamin/Multielement Tablets 

(data summary view – sample preparation method)..............................................41

Figure 17. Thiamine hydrochloride in SRM 3252 Protein Drink Mix (data summary view 

– sample preparation method)................................................................................42

Figure 18. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view – sample preparation method).......................................................................43

Figure 19. Riboflavin in SRM 3252 Protein Drink Mix (data summary view – sample 

preparation method)...............................................................................................44

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

view – sample preparation method).......................................................................45
iv

Figure 21. Niacinamide in SRM 3252 Protein Drink Mix (data summary view – sample 

preparation method)...............................................................................................46

Figure 22. Thiamine hydrochloride in SRM 3280 Multivitamin/Multielement Tablets 

(data summary view – instrumental method).........................................................47

Figure 23. Thiamine hydrochloride in SRM 3252 Protein Drink Mix (data summary view 

– instrumental method) ..........................................................................................48

Figure 24. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view – instrumental method) .................................................................................49

Figure 25. Riboflavin in SRM 3252 Protein Drink Mix (data summary view – instrumental

method) ..................................................................................................................50

Figure 26. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view – instrumental method) .................................................................................51

Figure 27. Niacinamide in SRM 3252 Protein Drink Mix (data summary view –

instrumental method) .............................................................................................52

Figure 28. Thiamine hydrochloride in SRM 3280 Multivitamin/Multielement Tablets 

(data summary view – calibration method) ...........................................................53

Figure 29. Thiamine hydrochloride in SRM 3252 Protein Drink Mix (data summary view 

– calibration method).............................................................................................54

Figure 30. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view – calibration method) ....................................................................................55

Figure 31. Riboflavin in SRM 3252 Protein Drink Mix (data summary view – calibration 

method) ..................................................................................................................56

Figure 32. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets (data summary 

view – calibration method) ....................................................................................57

Figure 33. Niacinamide in SRM 3252 Protein Drink Mix (data summary view –

calibration method)................................................................................................58

Figure 34. Thiamine HCl in SRM 3280 Multivitamin/Multielement Tablets and SRM 

3252 Protein Drink Mix (sample/sample comparison view).................................59

Figure 35. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets and SRM 3252 

Protein Drink Mix (sample/sample comparison view)..........................................60

Figure 36. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets and SRM 3252 

Protein Drink Mix (sample/sample comparison view)..........................................61

VITAMIN K IN DIETARY SUPPLEMENTS..........................................................................62

Study Overview .................................................................................................................62

Sample Information ...........................................................................................................62

Multivitamin/Multielement Tablets.......................................................................62

Protein Powder.......................................................................................................62

Study Results .....................................................................................................................62

Technical Recommendations.............................................................................................63

Table 10. Individualized data summary table (NIST) for vitamin K1 in dietary 

supplements............................................................................................................64

Table 11. Data summary table for vitamin K1 in dietary supplements............................65

Figure 37. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets (data 

summary view – sample preparation method).......................................................66
v

Figure 38. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets (data 

summary view – instrumental method)..................................................................67

Figure 39. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets (data 

summary view – calibration method) ....................................................................68

Figure 40. Phylloquinone in SRM 3252 Protein Drink Mix (data summary view).........69

Figure 41. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets and SRM 

3252 Protein Drink Mix (sample/sample comparison view).................................70

ACRYLAMIDE IN CHOCOLATE AND COFFEE ................................................................71

Study Overview .................................................................................................................71

Sample Information ...........................................................................................................71

Baking Chocolate...................................................................................................71

Coffee.....................................................................................................................71

Study Results .....................................................................................................................71

Technical Recommendations.............................................................................................72

Table 12. Individualized data summary table (NIST) for acrylamide in chocolate and 

coffee......................................................................................................................73

Table 13. Data summary table for acrylamide in chocolate and coffee ...........................74

Figure 42. Acrylamide in SRM 2384 Baking Chocolate (data summary view – sample 

preparation method)...............................................................................................75

Figure 43. Acrylamide in SRM 2384 Baking Chocolate (data summary view –

instrumental method) .............................................................................................76

Figure 44. Acrylamide in SRM 2384 Baking Chocolate (data summary view – calibration

method) ..................................................................................................................77

Figure 45. Acrylamide in roasted coffee beans (data summary view).............................78

Figure 46. Acrylamide in SRM 2384 Baking Chocolate and roasted coffee beans

(sample/sample comparison view).........................................................................79

PHYTOSTEROLS IN SAW PALMETTO ...............................................................................80

Study Overview .................................................................................................................80

Sample Information ...........................................................................................................80

Saw Palmetto Fruit.................................................................................................80

Saw Palmetto Extract.............................................................................................80

Study Results .....................................................................................................................81

Technical Recommendations.............................................................................................81

Table 14. Individualized data summary table (NIST) for phytosterols in saw palmetto 

dietary supplements ...............................................................................................83

Table 15. Data summary table for campesterol in saw palmetto dietary supplements....84

Table 16. Data summary table for β–sitosterol in saw palmetto dietary supplements.....85

Table 17. Data summary table for stigmasterol in saw palmetto dietary supplements....86

Figure 47. Campesterol in SRM 3250 Serenoa repens Fruit (data summary view – sample

preparation method)...............................................................................................87

Figure 48. Campesterol in SRM 3251 Serenoa repens Extract (data summary view –

sample preparation method)...................................................................................88

Figure 49. β-sitosterol in SRM 3250 Serenoa repens Fruit (data summary view – sample 

preparation method)...............................................................................................89
vi

Figure 50. β-sitosterol in SRM 3251 Serenoa repens Extract (data summary view – sample 

preparation method)...............................................................................................90

Figure 51. Stigmasterol in SRM 3250 Serenoa repens Fruit (data summary view – sample 

preparation method)...............................................................................................91

Figure 52. Stigmasterol in SRM 3251 Serenoa repens Extract (data summary view –

sample preparation method)...................................................................................92

Figure 53. Campesterol in SRM 3250 Serenoa repens Fruit (data summary view –

instrumental method) .............................................................................................93

Figure 54. Campesterol in SRM 3251 Serenoa repens Extract (data summary view –

instrumental method) .............................................................................................94

Figure 55. β-sitosterol in SRM 3250 Serenoa repens Fruit (data summary view –

instrumental method) .............................................................................................95

Figure 56. β-sitosterol in SRM 3251 Serenoa repens Extract (data summary view –

instrumental method) .............................................................................................96

Figure 57. Stigmasterol in SRM 3250 Serenoa repens Fruit (data summary view –

instrumental method) .............................................................................................97

Figure 58. Stigmasterol in SRM 3251 Serenoa repens Extract (data summary view –

instrumental method) .............................................................................................98

Figure 59. Campesterol in SRM 3250 Serenoa repens Fruit (data summary view –

calibration approach) .............................................................................................99

Figure 60. Campesterol in SRM 3251 Serenoa repens Extract (data summary view –

calibration approach) ...........................................................................................100

Figure 61. β-sitosterol in SRM 3250 Serenoa repens Fruit (data summary view –

calibration approach) ...........................................................................................101

Figure 62. β-sitosterol in SRM 3251 Serenoa repens Extract (data summary view –

calibration approach) ...........................................................................................102

Figure 63. Stigmasterol in SRM 3250 Serenoa repens Fruit (data summary view –

calibration approach) ...........................................................................................103

Figure 64. Stigmasterol in SRM 3251 Serenoa repens Extract (data summary view –

calibration approach) ...........................................................................................104

Figure 65. Campesterol in SRM 3250 Serenoa repens Fruit and SRM 3251 Serenoa 

repens Extract (sample/sample comparison view) ..............................................105

Figure 66. β-sitosterol in SRM 3250 Serenoa repens Fruit and SRM 3251 Serenoa repens

Extract (sample/sample comparison view)..........................................................106

Figure 67. Stigmasterol in SRM 3250 Serenoa repens Fruit and SRM 3251 Serenoa 

repens Extract (sample/sample comparison view) ..............................................107

Figure 68. Comparison of results for campesterol in SRM 3250 Saw Palmetto Fruit from 

Exercise H (left) and Exercise K (right) ..............................................................108

Figure 69. Comparison of results for β-sitosterol in SRM 3250 Saw Palmetto Fruit from 

Exercise H (left) and Exercise K (right) ..............................................................109
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 including the dietary 

supplement current good manufacturing practices (cGMPs). Exercise K of this program offered 

the opportunity for laboratories to assess their in-house measurements of nutritional elements (P

and Fe), contaminants (mercury and acrylamide), water-soluble vitamins (vitamins B1, B2, and 

B3), fat-soluble vitamins (vitamin K1), and phytosterols 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 and worldwide 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 Federal 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. In addition, the DSHEA authorized the establishment of the Office of Dietary

Supplements at the National Institutes of Health (NIH ODS). 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 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 AOAC INTERNATIONAL Official Method of Analysis would benefit the dietary 

supplement community.

NIST has experience in the administration 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 and improve laboratory 

 

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

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

performance. In contrast, the wide range of matrices and analytes under the “dietary supplement” 

umbrella means that not 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 eleventh exercise of the DSQAP, Exercise K. Eightyone laboratories responded to the call for participants distributed in December 2013. Samples 

were shipped to participants in February 2014, and results were returned to NIST by May 2014. 

This report contains the final data and information that was disseminated to the participants in 

November 2014.

OVERVIEW OF DATA TREATMENT AND REPRESENTATION

Individualized data tables and certificates are provided to the participants that have submitted data 

in each study, in addition to this report. Examples of the data tables using NIST data are also 

included in each section of this report. Community tables and graphs are provided using 

randomized laboratory codes, with identities known only to NIST and individual laboratories. The 

statistical approaches are outlined below for each type of data representation.

Statistics

Data tables and graphs throughout this report 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.

 

2

ISO 13528:2005(E), Statistical methods for use in proficiency testing by interlaboratory comparisons, pp 14-15.
3

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*:

x* = ∑ xi

n ∗

i=1

n

s* = 1.134 × √

∑ (xi

∗−x

∗)

n

i=1

n−1

.

Individualized 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).
4

 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).

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.3 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 or by measurements obtained from collaborating laboratories. 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 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. Where appropriate, two consensus 

means may be calculated for the same sample if bimodality is identified in the data. In this case, 

two consensus means and ranges will be displayed in the data summary view. 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 

 

3

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

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. The major program goals are

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

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, analysis, 

or quantitation.

Sample/Sample Comparison View

In this view, the individual laboratory results for one sample (NIST SRM with a certified or 

reference value) are compared to the results for another sample (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 first sample (x-axis) and 

the second sample (y-axis). The dotted blue box represents the consensus zone for the first sample 

(x-axis) and the second sample (y-axis). The axes of this graph are centered about the consensus 

mean values for each sample or control, to a limit of zero and twice the consensus mean. 

Depending on the variability in the data, the axes may be scaled proportionally to better display 

the individual data points for each laboratory. In some cases, when the consensus and target ranges 

have limited overlap, the solid red box may only appear partially on the graph. If the variability 

in the data is high (greater than 100 % relative standard deviation (RSD)), the dotted blue box may 

also only appear partially on the graph. 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

NUTRITIONAL ELEMENTS (P, Fe) IN CRANBERRY AND BLUEBERRY

Study Overview 

In this study, participants were provided with two NIST SRMs, SRM 3281 Cranberry (Fruit) and 

SRM 3287 Blueberry (Fruit). Participants were asked to use in-house analytical methods to 

determine the mass fractions of two nutritional elements (phosphorus and iron) in each of the 

matrices and report values on an as-received basis. 

Sample Information 

Cranberry. Participants were provided with one packet containing approximately 6 g of freezedried, powdered cranberries. The cranberry powder was blended, aliquotted, and heat-sealed 

inside 4 mil polyethylene bags, which were then sealed inside nitrogen-flushed aluminized plastic 

bags along 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 0.5 g. Participants were asked to 

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

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

reported to participants prior to the study. The reference values in SRM 3281 Cranberry (Fruit) 

were determined at NIST using inductively coupled plasma optical emission spectroscopy (ICPOES). The reference values and uncertainties for P and Fe are provided in the table below, both 

on a dry-mass basis and on an as-received basis accounting for moisture of the material (2.39 %).

Reference Mass Fraction in SRM 3281 (mg/kg)

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

Phosphorus (P) 835 ± 17 815 ± 17

Iron (Fe) 27.7 ± 0.7 27.0 ± 0.7

Blueberry. Participants were provided with one packet containing approximately 5 g of freezedried, powdered blueberries. The blueberry powder was blended, aliquotted, and heat-sealed 

inside 4 mil polyethylene bags, which were then sealed inside nitrogen-flushed aluminized plastic 

bags along 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 0.5 g. Participants were informed 

that this material was packaged as a powder; however, over time the powder may have become a 

solid mass, and for hardened samples, an appropriate test portion should be removed and 

subdivided using a knife. Participants were asked to store the material at controlled room 

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

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

The certified values in SRM 3287 Blueberry (Fruit) were determined at NIST using ICP-OES in 

combination with data from numerous collaborating laboratories. The certified values and 

uncertainties for P and Fe are provided in the table below, both on a dry-mass basis and on an asreceived basis accounting for moisture of the material (1.41 %).
7

Certified Mass Fraction in SRM 3287 (mg/kg)

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

Phosphorus (P) 671 ± 21 662 ± 21

Iron (Fe) 12.2 ± 0.7 12.0 ± 0.7

Study Results 

 Fifty-one laboratories enrolled in this exercise and received samples. Thirty-eight

laboratories reported results for phosphorus (75 % participation). Forty-two laboratories 

reported results for iron (82 % participation). 

 The consensus means for phosphorus in both materials and for iron in the cranberries were 

below the target range.

 The between-laboratory variability for phosphorus determination was acceptable in 

both materials (14 % to 16 % RSD).

 The between-laboratory variability for iron determination was high in the cranberry 

material (22 % RSD).

 The consensus mean for iron in the blueberry material was at the upper limit of the target 

range with a high between-laboratory variability (32 % RSD).

 A majority of the laboratories reported using either microwave digestion (63 %) or openbeaker digestion (28 %) for sample preparation. The remaining laboratories reported using

hot block digestion or dry ashing. Two laboratories did not report the type of sample 

preparation technique that was used.

 A majority of the laboratories reported using either ICP-MS (52 %) or ICP-OES (42 %) as 

their analytical method. Three laboratories reported using atomic absorption spectroscopy 

(AAS, 7 %), and one laboratory did not report the type of analytical technique that was 

used.

 A majority of the laboratories reported using an external standard approach to calibration 

(88 %). Four laboratories reported using a standard addition approach (10 %), and two 

laboratories reported using an internal standard approach (5 %). One laboratory did not 

report the type of calibration approach that was used.

Technical Recommendations 

The following recommendations are based on results obtained from the participants in this study.

 No difference was apparent between results obtained using either open beaker or 

microwave digestion for phosphorus or iron. Too few results were reported by other 

methods to identify any additional trends. 

 No difference was apparent in the iron results based on analytical method used (ICP-OES 

or ICP-MS). 

 As shown in Figure 10, some laboratories reported acceptable or high values for one 

sample but low values for the second sample.

 This may indicate more difficulty in the digestion of one material over the other. 

Laboratories that reported using a more aggressive digestion, using high heat and 

concentrated acid, generally had values in the middle of the consensus range or 

target range.
8

 This may also be an indicator of a larger matrix interference with one material 

versus the other during analysis. The use of an internal standard may alleviate this 

problem, especially when using ICP-OES.

 A slight difference in phosphorous results based on analytical method was identified.

 In Figure 9, results that are low for phosphorous for both materials were analyzed using 

ICP-MS. 

 Phosphorous may be difficult to analyze by ICP-MS. Since there is only one mass 

available for phosphorous the use of a collision cell or reaction cell is needed to 

eliminate polyatomic interferences.

 There may also be calibration issues for phosphorus that were not evident for iron. To 

avoid calibration problems, be sure to include the lowest and highest expected values 

in the calibration curve, plus one or two intermediate concentration points. 

 Ensure that the calibration curve is linear and surrounds expected sample 

concentrations following digestion and/or dilution. Samples should not go beyond the 

linear range of the calibration curve, as this results in extrapolation of calibration curves 

and the possibility of obtaining false values.

 Quality assurance samples should always be used. These can be commercially available 

reference materials (CRMs, SRMs, or RMs) or prepared in-house, but need to be of known 

concentration.

 They are used to ensure that your method is performing as expected.

 They are useful in finding where errors are occurring, including calculation errors.

 After checking for calculation errors, make sure results are reported correctly.
9

Table 1. Individualized data summary table (NIST) for nutritional elements in cranberry and blueberry.

Lab Code: NIST

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U 95

P Cranberries mg/kg 815 17 0.8 0.0 38 726 105 815 17

P Blueberries mg/kg 662 21 0.7 0.0 38 593 94 662 33

Fe Cranberries mg/kg 27.0 0.7 0.4 0.0 42 24.7 5.4 27.0 0.7

Fe Blueberries mg/kg 12.0 0.7 -0.3 0.0 42 13.5 4.3 12.0 0.7

xi Mean of reported values N Number of quantitative xNIST NIST-assessed value

si Standard deviation of reported values values reported U95 ±95% confidence interval

Zcomm Z-score with respect to community x* Robust mean of reported about the assessed value or

 consensus values standard deviation (sNIST)

ZNIST Z-score with respect to NIST value s* Robust standard deviation

Exercise K - February 2014 - Nutritional Elements

1. Your Results 2. Community Results 3. Target

National Institute of Standards & Technology
10

Table 2. Data summary table for phosphorus in cranberry and blueberry.

Lab A B C Avg SD A B C Avg SD

NIST 815 17 662 21

K002

K003 776 774 776 775 1 654 652 641 649 7

K004 1035 1060 1043 1046 13 1028 1010 1003 1014 13

K005 756 755 752 754 2 623 618 625 622 4

K007 623 621 626 623 2 494 491 497 494 3

K008

K010

K011 828 867 807 834 30 723 671 705 700 26

K012 757 755 759 757 2 611 610 617 613 4

K013 739 721 737 732 10 577 593 586 585 8

K014

K015 647 694 654 665 25 556 658 642 618 55

K016 698 686 694 693 6 546 533 529 536 9

K018 913 918 928 920 8 755 749 753 752 3

K024 630 642 606 626 18 468 482 496 482 14

K025 786 789 743 773 26 628 639 600 622 20

K027

K028 226 259 292 259 33 213 215 221 216 4

K029 21 21 20 21 1 11 10 10 10 0

K031 718 735 749 734 16 578 589 571 579 9

K034 859 874 877 870 10 690 701 702 698 7

K038 828 802 874 835 36 666 637 679 661 21

K039 770 770 770 770 0 610 630 620 620 10

K040

K042 737 710 702 717 18 578 550 562 563 14

K045 796 764 809 790 23 628 653 622 634 16

K046

K048 751 741 745 746 5 598 600 583 594 9

K049 749 768 772 763 12 659 659 662 660 2

K051 861 919 900 893 30 676 708 681 688 17

K054

K056 791 786 709 762 46 622 646 601 623 23

K057 775 779 776 777 2 608 638 622 623 15

K058 610 630 620 620 10 620 660 690 657 35

K060 617 604 626 616 11 768 754 762 761 7

K061

K064 828 844 830 834 8 665 676 665 669 6

K066 775 759 794 776 17 598 589 599 596 6

K068

K069

K071 706 727 715 716 11 563 559 565 562 3

K072 617 637 617 624 12 483 462 467 471 11

K073 722 731 728 727 5 531 546 537 538 8

K074 677 688 699 688 11 528 537 531 532 4

K075 682 684 688 685 3 543 543 544 543 1

K076

K077

K078 706 679 676 687 17 564 543 541 549 13

K079 687 687 668 681 11 551 572 547 556 14

K080 21 19 20 20 1 11 10 10 10 0

K081 24 24 25 24 1 13 14 14 1

 Consensus Mean 726 Consensus Mean 593

 Consensus Standard Deviation 105 Consensus Standard Deviation 94

 Maximum 1046 Maximum 1014

 Minimum 20 Minimum 10

 N 38 N 38

Phosphorus

SRM 3281 Cranberries (mg/kg) SRM 3287 Blueberries (mg/kg) Community Results Individual Results
11

Table 3. Data summary table for iron in cranberry and blueberry.

Lab A B C Avg SD A B C Avg SD

NIST 27.0 0.7 12.0 0.7

K002 14.0 13.0 22.0 16.3 4.9 38.0 45.0 32.0 38.3 6.5

K003 24.9 24.5 24.3 24.6 0.3 12.3 11.1 11.6 11.7 0.6

K004 12.9 12.5 12.9 12.8 0.3 13.9 14.7 14.0 14.2 0.4

K005 33.5 35.0 33.7 34.1 0.8 28.6 31.0 27.2 28.9 1.9

K007 23.3 22.6 23.5 23.1 0.5 11.7 10.6 11.5 11.3 0.6

K008 23.4 22.8 21.5 22.6 1.0 11.7 12.1 11.0 11.6 0.6

K010

K011 15.4 17.3 14.2 15.6 1.6 4.6 3.7 4.7 4.3 0.5

K012 22.6 22.1 23.0 22.6 0.5 10.7 10.7 11.2 10.9 0.3

K013 20.0 22.1 20.6 20.9 1.1 10.3 10.6 11.1 10.7 0.4

K014 21.9 20.3 20.8 21.0 0.8 9.5 8.9 9.4 9.3 0.3

K015 40.3 34.1 34.3 36.2 3.5 26.2 21.5 27.6 25.1 3.2

K016 32.2 22.1 23.3 25.9 5.5 13.1 11.7 10.8 11.9 1.2

K018 21.6 21.8 22.4 21.9 0.4 9.9 9.9 9.9 9.9 0.0

K024 29.0 29.4 29.8 29.4 0.4 17.1 17.5 17.5 17.4 0.3

K025 20.9 20.3 20.4 20.5 0.3 17.8 14.6 10.6 14.3 3.6

K027 18.9 19.4 19.9 19.4 0.5 23.2 22.7 22.3 22.8 0.5

K028 21.5 20.0 20.4 20.6 0.8 13.0 12.8 13.8 13.2 0.5

K029 758.7 769.1 732.0 753.2 19.1 579.1 581.7 537.0 565.9 25.1

K031 24.3 24.5 24.9 24.6 0.3 9.6 9.9 10.3 10.0 0.3

K034 31.7 27.9 37.6 32.4 4.9 16.7 20.9 18.4 18.7 2.1

K038 23.2 30.1 25.0 26.1 3.6 7.1 6.8 7.0 6.9 0.2

K039 25.4 22.3 23.4 23.7 1.6 11.2 10.9 11.0 11.0 0.2

K040

K042 31.7 27.0 26.7 28.5 2.8 10.0 10.4 10.6 10.3 0.3

K045 29.5 28.7 28.4 28.9 0.6 11.2 12.2 10.9 11.4 0.7

K046

K048 22.1 22.9 24.1 23.0 1.0 11.5 10.5 9.5 10.5 1.0

K049 22.8 23.9 23.5 23.4 0.6 10.9 10.9 10.6 10.8 0.2

K051 28.4 23.7 23.1 25.1 2.9 18.8 11.8 13.1 14.6 3.7

K054 16.1 16.3 16.2 16.2 0.1 12.1 12.3 12.2 12.2 0.1

K056 22.8 22.7 22.5 22.7 0.2 10.7 10.0 10.1 10.3 0.4

K057 25.0 24.6 24.1 24.5 0.5 10.6 11.4 11.1 11.0 0.4

K058 21.0 24.0 17.0 20.7 3.5 14.0 12.0 12.0 12.7 1.2

K060 27.8 25.3 27.7 26.9 1.4 21.7 11.6 18.3 17.2 5.2

K061

K064 24.4 24.8 24.3 24.5 0.3 11.2 11.0 10.9 11.0 0.2

K066

K068

K069

K071 29.0 36.0 44.0 36.3 7.5 17.0 16.0 19.0 17.3 1.5

K072 23.8 24.0 23.6 23.8 0.2 10.8 10.8 10.4 10.6 0.2

K073 22.3 23.6 23.7 23.2 0.8 12.2 15.5 10.8 12.8 2.4

K074 28.8 25.3 23.1 25.7 2.9 13.7 12.2 16.8 14.2 2.4

K075 22.2 23.3 35.2 26.9 7.2 12.4 13.2 12.4 12.7 0.5

K076

K077

K078 22.9 24.6 29.9 25.8 3.6 13.8 13.0 16.5 14.4 1.8

K079 21.7 22.4 21.5 21.9 0.5 12.5 14.2 11.9 12.8 1.2

K080 714.0 681.3 720.6 705.3 21.1 578.1 544.4 555.8 559.4 17.1

K081 691.7 682.1 715.4 696.4 17.1 554.0 557.7 562.4 558.0 4.2

 Consensus Mean 24.7 Consensus Mean 13.5

 Consensus Standard Deviation 5.4 Consensus Standard Deviation 4.3

 Maximum 753.2 Maximum 565.9

 Minimum 12.8 Minimum 4.3

 N 42 N 42

Iron

SRM 3281 Cranberries (mg/kg) SRM 3287 Blueberries (mg/kg) Individual Results Community Results
12

Figure 1. Phosphorus in SRM 3281 Cranberry (Fruit) (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. 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 bounded by twice its uncertainty (U95).
13

Figure 2. Phosphorus in SRM 3287 Blueberry (Fruit) (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. 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 3. Iron in SRM 3281 Cranberry (Fruit) (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. 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 bounded by twice its uncertainty (U95).
15

Figure 4. Iron in SRM 3287 Blueberry (Fruit) (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. 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 5. Phosphorus in SRM 3281 Cranberry (Fruit) (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. 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 bounded by twice its uncertainty (U95).
17

Figure 6. Phosphorus in SRM 3287 Blueberry (Fruit) (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. 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 7. Iron in SRM 3281 Cranberry (Fruit) (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. 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 bounded by twice its uncertainty (U95).
19

Figure 8. Iron in SRM 3287 Blueberry (Fruit) (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. 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).
20

Figure 9. Phosphorus in SRM 3287 Blueberry (Fruit) and SRM 3281 Cranberry (Fruit) 

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

(blueberry) are compared to the results for a second sample (cranberry). The solid red box 

represents the target zone for the two samples, blueberry (x-axis) and cranberry (y-axis). The 

dotted blue box represents the consensus zone for blueberry (x-axis) and cranberry (y-axis).
21

Figure 10. Iron in SRM 3287 Blueberry (Fruit) and SRM 3281 Cranberry (Fruit) (sample/sample 

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

compared to the results for a second sample (cranberry). The solid red box represents the target 

zone for the two samples, blueberry (x-axis) and cranberry (y-axis). The dotted blue box represents 

the consensus zone for blueberry (x-axis) and cranberry (y-axis).
22

TOXIC ELEMENTS (Hg) IN EPHEDRA AND GINKGO DIETARY SUPPLEMENTS

Study Overview

In this study, participants were provided with two NIST SRMs, SRM 3240 Ephedra sinica Stapf

Aerial Parts and SRM 3246 Ginkgo biloba (Leaves). Participants were asked to use in-house 

analytical methods to determine the mass fractions of mercury (Hg) in each of the matrices and 

report values on an as-received basis. 

Sample Information

Ephedra Aerial Parts. Participants were provided with one bottle containing approximately 5 g 

of dried Ephedra sinica Stapf aerial parts. The dried leaves were ground, homogenized, and 

packaged under nitrogen inside amber high-density polyethylene bottles with polypropylene screw 

caps. Before use, participants were instructed to thoroughly mix the contents of the bottle and use 

a sample size of at least 0.2 g. Participants were asked to store the material at controlled room 

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

bottle provided. Approximate analyte levels were not reported to participants prior to the study. 

The certified value for mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts was determined 

at NIST using cold-vapor generation isotope dilution inductively coupled plasma mass 

spectrometry (CV-ID-ICP-MS) and at the US Food and Drug Administration (FDA) using ICPMS. The certified value and uncertainty for Hg are provided in the table below, both on a drymass basis and on an as-received basis accounting for moisture of the material (4.52 %).

Certified Mass Fraction in SRM 3240 (ng/g)

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

Mercury (Hg) 16.7 ± 0.5 15.9 ± 0.5

Ginkgo Leaves. Participants were provided with one bottle containing approximately 3 g of dried 

Ginkgo biloba leaves. The dried leaves were ground, homogenized, and packaged under nitrogen 

inside amber high-density polyethylene bottles with polypropylene screw caps. Before use, 

participants were instructed to thoroughly mix the contents of the bottle and use a sample size of 

at least 0.25 g. Participants were asked to store the material at controlled room temperature, 10 °C 

to 30 °C, and to prepare three samples and report three values from the single bottle provided. 

Approximate analyte levels were not reported to participants prior to the study. The certified value 

for mercury in SRM 3246 Ginkgo biloba (Leaves) was determined at NIST using CV-ID-ICP-MS. 

The certified value and uncertainty for Hg are provided in the table below, both on a dry-mass 

basis and on an as-received basis accounting for moisture of the material (4.82 %).

Certified Mass Fraction in SRM 3246 (ng/g)

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

Mercury (Hg) 23.08 ± 0.17 21.97 ± 0.16

Study Results

 Fifty-four laboratories enrolled in this exercise and received samples. Forty-three

laboratories reported results for mercury in Ephedra aerial parts (80 % participation). 

Forty-four laboratories reported results for mercury in Ginkgo leaves (82 % participation).
23

 The consensus means for mercury in both matrices were within the target range but with

high variability (20 % and 30 % RSD for the Ephedra and Ginkgo, respectively).

 A majority of the laboratories reported using microwave digestion (68 %) for sample 

preparation. Ten laboratories reported using open beaker digestion (25 %). Hot block 

digestion (3 %) and thermal decomposition (3 %) were also reported as methods of sample 

preparation. One laboratory reported doing no sample preparation, and one laboratory did 

not report the type of sample preparation used.

 Most laboratories reported using ICP-MS as their analytical method for analysis (85 %). 

Laboratories also reported using AAS (7 %), cold vapor AAS (2 %), ICP-OES (2 %), and 

a direct mercury analyzer (2 %). One laboratory did not report the analytical method used.

 A majority of the laboratories reported using an external standard approach to calibration 

(90 %). One laboratory reported using a standard addition approach (2 %), and three 

laboratories reported using an internal standard approach (7 %). Two laboratories did not 

report the type of calibration approach that was used.

Technical Recommendations

The following recommendations are based on results obtained from the participants in this study.

 Mercury is volatile, so care must be taken to not lose Hg during sample preparation. 

Microwave digestion is the best method for sample preparation.

 Plant materials can be difficult to digest without the use of HF. 

 Low concentrations of Hg are not stable in solution over long periods of time. Samples 

are best prepared close to the time of analysis.

 Samples containing low concentrations of Hg may be more stable in dilute HCl than in 

dilute HNO3.

 Mercury is at very low levels in both materials and may be close to method detection limits. 

 Use a good calibration curve with low concentrations to help with accuracy.

 Mercury blanks and backgrounds may be large, making it difficult to determine lowlevel samples.

 Use a sufficient number of blanks so an accurate method detection limit and limit of 

quantitation can be determined.

 Values reported at the higher end of the range had more within-laboratory variability. This 

was most likely due to contamination issues, or problems with sample analysis such as

memory effects.

 Mercury has a poor washout (long memory effect) and can give erratic answers if an 

adequate washout time is not used after each measurement. Use of dilute HCl may decrease 

the length of necessary washout time.

 The sensitivity of Hg is low when using ICP-MS or ICP-OES. Using cold vapor mercury 

generation increases sensitivity allowing for lower levels of Hg to be measured.

 Run a quality assurance sample of known concentration to ensure your method is 

performing as expected. An appropriate control is one that will mirror both the sample 

matrix and the mass fraction levels expected to be found in the sample.

 Double-check all calculations for any errors.
24

Table 4. Individualized data summary table (NIST) for mercury in Ephedra and Ginkgo dietary supplements.

Lab Code: NIST

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U 95

Hg Ephedra Aerial Parts ng/g 15.9 0.5 -0.1 0.0 43 16.5 4.9 15.9 0.5

Hg Ginkgo Leaves ng/g 22.0 0.2 -0.1 0.0 44 22.3 4.6 22.0 0.2

xi Mean of reported values N Number of quantitative xNIST NIST-assessed value

si Standard deviation of reported values values reported U95 ±95% confidence interval

Zcomm Z-score with respect to community x* Robust mean of reported about the assessed value or

 consensus values standard deviation (sNIST)

ZNIST Z-score with respect to NIST value s* Robust standard deviation

Exercise K - February 2014 - Toxic Elements

1. Your Results 2. Community Results 3. Target

National Institute of Standards & Technology
25

Table 5. Data summary table for mercury in Ephedra and Ginkgo dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 15.9 0.5 22.0 0.2

K002 15.3 14.3 15.2 14.9 0.5 25.4 23.6 21.9 23.6 1.8

K003 15.5 14.3 15.2 15.0 0.6 26.1 24.5 20.9 23.8 2.7

K004

K005 16.2 14.1 14.7 15.0 1.1

K007 19.1 22.5 19.4 20.3 1.9 25.5 37.7 29.5 30.9 6.2

K010

K011 285.0 285.0 271.0 280.3 8.1 314.0 302.0 295.0 303.7 9.6

K013 17.9 15.9 16.1 16.6 1.1 24.2 28.1 22.7 25.0 2.8

K016 15.1 13.0 12.0 13.4 1.6 18.4 17.0 17.6 17.7 0.7

K018 18.1 17.2 18.4 17.9 0.6 27.4 26.5 27.3 27.1 0.5

K023 15.7 15.8 15.6 15.7 0.1 23.1 22.7 23.2 23.0 0.3

K024 26.2 22.8 19.1 22.7 3.6 21.6 21.5 20.3 21.1 0.7

K025 19.8 19.9 20.0 19.9 0.1 19.7 19.9 19.7 19.8 0.1

K027 24.7 24.6 30.1 26.5 3.2 14.5 15.2 14.0 14.6 0.6

K028 4.6 4.2 4.0 4.3 0.3 4.5 4.5 4.6 4.5 0.1

K029 11.4 10.9 11.4 11.2 0.3 19.3 19.3 19.4 19.3 0.1

K030 13.2 14.7 13.4 13.8 0.8 22.6 20.5 26.0 23.0 2.8

K031 14.0 15.0 14.7 14.6 0.5 21.2 21.4 22.0 21.5 0.4

K034 16.4 16.4 16.4 16.4 0.0 23.0 23.0 24.0 23.3 0.6

K037 42.0 37.0 40.0 39.7 2.5 28.0 25.0 25.0 26.0 1.7

K039 20.4 20.8 21.5 20.9 0.6 19.6 21.2 21.0 20.6 0.9

K040

K042 21.5 20.3 20.7 20.8 0.6 24.8 28.4 27.3 26.8 1.8

K045 16.8 17.9 19.3 18.0 1.3 24.4 27.5 25.8 25.9 1.6

K046 16.1 15.7 16.4 16.1 0.4 22.2 22.0 21.1 21.8 0.6

K047 17.6 17.9 17.7 0.2 24.9 23.8 24.3 0.8

K048 12.9 14.0 12.4 13.1 0.8 17.7 17.9 16.7 17.4 0.6

K049 32.4 18.6 16.7 22.6 8.6 44.2 29.8 26.0 33.3 9.6

K050 18.0 18.9 18.4 18.4 0.5 23.3 22.1 22.5 22.6 0.6

K051 5.4 7.0 7.5 6.6 1.1 17.8 18.7 18.1 18.2 0.4

K052 14.5 13.8 14.0 14.1 0.3 20.5 21.0 20.6 20.7 0.3

K056 12.0 11.0 12.0 11.7 0.6 22.0 22.0 22.0 22.0 0.0

K057 16.4 16.6 16.3 16.4 0.2 23.0 24.2 24.3 23.8 0.7

K058 14.0 15.0 17.0 15.3 1.5 23.0 21.0 22.0 22.0 1.0

K059 14.4 13.7 11.9 13.3 1.3 34.9 21.0 24.6 26.8 7.2

K060 18.0 13.0 24.0 18.3 5.5 22.0 19.0 51.0 30.7 17.7

K061

K062 10.9 8.9 10.0 9.9 1.0 14.4 15.9 15.6 15.3 0.8

K063 25.8 25.2 24.3 25.1 0.8 17.1 16.0 17.2 16.8 0.7

K064

K065 18.1 21.3 24.3 21.2 3.1 25.3 25.6 29.1 26.6 2.1

K066 12.0 13.7 14.0 13.2 1.1 22.9 23.2 20.9 22.3 1.2

K067

K069

K070

K071 45.0 43.0 42.0 43.3 1.5 48.0 44.0 40.0 44.0 4.0

K072 14.8 13.3 13.5 13.9 0.8 21.4 21.8 22.0 21.7 0.3

K073 12.1 13.3 12.7 12.7 0.6 21.0 21.6 19.2 20.6 1.2

K074 14.0 14.3 14.1 14.2 0.2 23.0 22.2 22.9 22.7 0.4

K075 12.5 13.2 12.4 12.7 0.4 18.3 17.8 18.8 18.3 0.5

K076

K077

K078 12.5 12.6 12.9 12.7 0.2 21.0 19.0 18.5 19.5 1.3

K079 12.5 12.6 12.9 12.7 0.2 21.0 19.0 18.5 19.5 1.3

 Consensus Mean 16.5 Consensus Mean 22.3

 Consensus Standard Deviation 4.9 Consensus Standard Deviation 4.6

 Maximum 280.3 Maximum 303.7

 Minimum 4.3 Minimum 4.5

 N 43 N 44

Mercury

SRM 3240 Ephedra Aerial Parts (ng/g) SRM 3246 Ginkgo Leaves (ng/g) Community Results Individual Results
26

Figure 11. Mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts (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. 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).
27

Figure 12. Mercury in SRM 3246 Ginkgo biloba (Leaves) (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. 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 13. Mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts (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. 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).
29

Figure 14. Mercury in SRM 3246 Ginkgo biloba (Leaves) (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. 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 15. Mercury in SRM 3240 Ephedra sinica Stapf Aerial Parts and SRM 3246 Ginkgo biloba

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

sample (Ephedra leaves) are compared to the results for a second sample (Ginkgo leaves). The 

solid red box represents the target zone for the two samples, Ephedra leaves (x-axis) and Ginkgo 

leaves (y-axis). The dotted blue box represents the consensus zone for Ephedra leaves (x-axis) 

and Ginkgo leaves (y-axis).
31

WATER-SOLUBLE VITAMINS (B1, B2, B3) IN DIETARY SUPPLEMENTS

Study Overview 

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

Multielement Tablets, and one NIST candidate SRM, SRM 3252 Protein Drink Mix. Participants 

were asked to use in-house analytical methods to determine the mass fractions of vitamins B1, B2,

and B3 in each of the matrices and report values on an as-received basis. Participants were asked 

to report the vitamin B1, B2, and B3 content as thiamine hydrochloride, riboflavin, and niacinamide, 

respectively.

Sample Information 

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

multivitamin/multielement tablets. Before use, participants were instructed to grind all 30 tablets, 

mix the resulting powder thoroughly, and use a sample size of at least 0.25 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 

reported to participants prior to the study. The NIST certified values and uncertainties for vitamins

B1 and B3 in SRM 3280 were determined at NIST by LC with absorbance detection (LC-Abs) and 

isotope dilution liquid chromatography with mass spectrometric detection (ID-LC-MS) following 

solvent extraction, in combination with data from numerous collaborating laboratories. The NIST 

certified value and uncertainty for vitamin B2 in SRM 3280 were determined at NIST by LC-Abs

and LC-MS following solvent extraction, in combination with data from numerous collaborating 

laboratories. The certified values and uncertainties are reported in the table below, both on a drymass basis and on an as-received basis accounting for moisture of the material (1.37 %).

Certified Mass Fraction 

in SRM 3280 (mg/g)

Certified Mass Fraction

in SRM 3280 (mg/g)

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

Thiamine Hydrochloride (B1) 1.06 ± 0.12 1.05 ± 0.12

Riboflavin (B2) 1.32 ± 0.17 1.30 ± 0.17

Niacinamide (B3) 14.10 ± 0.23 13.91 ± 0.23

Protein Powder. Participants were provided with one packet containing approximately 10 g of 

protein powder. A mixture of commercially available chocolate protein drink mix powders was 

blended and heat-sealed inside nitrogen-flushed 4-mil plastic bags, which were heat-sealed inside 

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

participants were instructed to thoroughly mix the contents of the packet, and a sample size of at 

least 0.5 g was recommended. 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 reported to participants prior to the study. 

Certified values are not available for this material at the time of the report; NIST provided values 

for vitamins B1, B2, and B3 based on duplicate analysis from 10 packets using ID-LC-MS/MS. 

The NIST values in SRM 3252 Protein Drink Mix are reported in the table below with an estimated 

uncertainty based on twice the method standard deviation.
32

Analyte

Estimated Mass Fraction 

in SRM 3252 Protein Drink Mix (mg/kg)

Thiamine Hydrochloride (B1) 15.81 ± 0.66

Riboflavin (B2) 26.9 ± 2.9

Niacinamide (B3) 258.1 ± 8.7

Study Results

 Sixty laboratories enrolled in this exercise and received samples. Forty-one laboratories 

reported results for vitamins B1 and B3 in SRM 3280 (68 % participation) and 46

laboratories reported results for vitamin B2 in SRM 3280 (77 % participation). For the 

protein powder, the results of 25 laboratories were used in consensus calculations for

vitamin B1 (42 % participation), 30 laboratories for vitamin B2 (50 % participation), and 

29 laboratories for vitamin B3 (48 % participation). 

 The consensus mean was within the target range for vitamins B1 and B2 in SRM 3280. The 

variability in these measurements was excellent, with approximately 12 % RSD for both 

vitamins in the multivitamin sample.

 The consensus mean for vitamin B3 in the multivitamin was above the target range, but 

with excellent variability at 4 % RSD.

 A number of significantly outlying results were reported for the vitamins in the protein 

powder. These values varied from twice up to 100 times the expected value based on NIST 

data. As a result, target ranges were compared only to consensus means determined after 

these outlying data points had been excluded.

 Consensus means for vitamins B2 and B3 in the protein powder were within the target 

ranges. The between-laboratory variability for vitamin B3 was excellent (12 % RSD); 

the variability for vitamin B2 was significantly higher (31 % RSD).

 The consensus mean for vitamin B1 in the protein powder was slightly higher than the 

target range, with high between-laboratory variability (48 % RSD).

 The consensus means for the outlying data points were 18 times, 10 times, and 23 times 

greater than the target means for vitamins B1, B2, and B3, respectively.

 The consensus means for the outlying data points included 4 to 6 laboratory results, 

and had high to extremely high between-laboratory variability (23 % RSD, 57 % RSD, 

and more than 100 % RSD for vitamins B1, B2, and B3, respectively).

 A majority of the laboratories reported using solvent extraction (71 %) as the sample 

preparation method. Laboratories also reported using acid hydrolysis (19 %), base 

hydrolysis (7 %), and enzymatic hydrolysis (2 %). Two laboratories did not report the type 

of sample preparation used.

 A majority of the laboratories reported using LC-Abs (87 %) as their instrumental method 

for analysis. Use of spectrophotometry (8 %), LC-FL (3%), and LC/MS (3 %) were also 

reported. Two laboratories did not report the type of instrumental method used.

 A majority of the laboratories reported using an external standard approach to calibration 

(91 %). Laboratories also reported using standard addition (7 %) and internal standard 

(2 %) approaches to quantitation. Four laboratories did not report the quantitation approach 

used.
33

Technical Recommendations

The following recommendations are based on results obtained from the participants in this study.

 Results for the multivitamin tablet were excellent. No methods presented as significantly 

better or worse than any other. No systematic biases were noted.

 For the laboratories included in the determination of consensus mean for the protein drink 

mix, no methods presented as significantly better or worse than any other. No systematic 

biases were noted.

 Extreme outliers in the measurement of vitamins B1, B2, and B3 are likely a result of lack 

of specificity in the instrumental method.

 All of the outlying laboratories used LC-Abs for all three analytes.

 Some laboratories using LC-Abs may be experiencing a co-elution that would cause a 

high bias in the results.

 No specific wavelengths were identified as being problematic; because this is likely a 

coelution, the problem can likely be corrected by alteration of the chromatographic 

conditions.

 The following recommendations can help identify and avoid potential coelutions.

 A chromatographic method with alternate selectivity (different retention order) can 

be used as a check for each new sample type that is run. Ideally, the retention of 

coeluting compounds would also be affected and the results from the two 

chromatographic systems would be different. Two different responses would 

indicate a possible bias in one approach.

 A different detector can be used in series with an absorbance detector (as 

confirmation), such as a fluorescence detector or mass spectrometer. If a coeluting 

compound is present, the response from these detectors would be different than the 

response from the absorbance detector. Two different responses would indicate a 

possible bias in one approach.

 Considerations of potential interferences can assist in troubleshooting. For 

example, on many C18 systems, caffeine and thiamine have similar retention 

characteristics. Understanding the matrix that is being tested and possible coeluting 

compounds can be evaluated before a sample is analyzed for additional confidence 

in the result.
34

Table 6. Individualized data summary table (NIST) for water-soluble vitamins in dietary supplements.

Lab Code: NIST

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U 95

B1 Multivitamin mg/kg 1050 118 -0.6 0.0 41 1140 145 1045 118

B1 Protein Drink mg/kg 15.8 0.7 -0.6 0.0 25.0 37.2 36.3 15.8 0.7

B2 Multivitamin mg/kg 1300 168 -0.4 0.0 46 1370 164 1302 168

B2 Protein Drink mg/kg 26.9 2.9 -0.3 0.0 30 30.4 13.0 26.9 2.9

B3 Multivitamin mg/kg 13900 227 -1.5 0.0 41 14800 615 13907 227

B3 Protein Drink mg/kg 258 9 -0.6 0.0 29 291 55 258 9

xi Mean of reported values N Number of quantitative xNIST NIST-assessed value

si Standard deviation of reported values values reported U95 ±95% confidence interval

Zcomm Z-score with respect to community x* Robust mean of reported about the assessed value or

 consensus values standard deviation (sNIST)

ZNIST Z-score with respect to NIST value s* Robust standard deviation

Exercise K - February 2014 - Water-Soluble Vitamins

1. Your Results 2. Community Results 3. Target

National Institute of Standards & Technology
35

Table 7. Data summary table for vitamin B1 (thiamine hydrochloride) in dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 1045 118 15.8 0.7

K001 1124 1119 1143 1129 13

K002

K003 1200 1200 1200 1200 0

K004 1136 1052 1116 1101 44

K006 994 975 981 983 10

K008 998 1009 1000 1002 6 285.0 250.0 255.0 263.3 18.9

K009 939 945 937 940 4

K010

K011 1218 1203 1202 1208 9 327.5 303.5 326.3 319.1 13.5

K012

K013

K014

K015 710 1159 946 938 224 19.1 39.1 29.1 14.2

K016

K018 1240 1240 40.0 40.0

K019

K020

K022 1109 1090 1018 1072 48 13.8 13.8 12.8 13.5 0.6

K024 2262 2132 2018 2137 122 118.1 143.0 125.2 128.8 12.8

K025 1200 1220 1210 1210 10 28.4 27.4 29.9 28.6 1.3

K026 1150 1140 1130 1140 10 16.6 15.8 15.0 15.8 0.8

K028 1809 1800 1790 1800 10 355.0 350.0 350.0 351.7 2.9

K029 1080 1090 1100 1090 10

K031 1110 1100 1110 1107 6 12.1 11.7 12.7 12.2 0.5

K032 1152 1145 1139 1145 7 13.7 11.4 12.6 12.6 1.2

K033 890 880 900 890 10 9.4 9.4 11.0 9.9 0.9

K034

K035

K036 954 848 849 884 61 23.3 16.4 25.7 21.8 4.8

K037 1150 1180 1200 1177 25

K040

K042 1060 1110 1040 1070 36

K043

K044 1100 1100 1100 1100 0 200.0 200.0 200.0 200.0 0.0

K045 930 930 930 930 0

K046

K047 1162 1161 1158 1160 2

K048

K049 1690 1550 1280 1507 208 14.0 10.0 13.0 12.3 2.1

K051 1230 1260 1250 1247 15 12.4 11.9 11.4 11.9 0.5

K056 1163 1174 1177 1171 7 16.4 17.4 14.4 16.1 1.5

K057 1319 1221 1277 1272 49

K058 1210 1250 1240 1233 21 14.5 13.1 13.6 13.7 0.7

K059 1099 1089 1075 1088 12 265.0 303.0 313.0 293.7 25.3

K062 1100 1020 1030 1050 44 19.0 19.0 15.0 17.7 2.3

K063 1330 1310 1290 1310 20

K064 1250 1180 1200 1210 36

K065 1130 1133 1143 1135 7

K066 1101 1139 1103 1115 21 10.3 14.6 11.7 12.2 2.2

K068

K069

K071 970 980 960 970 10

K073

K074 1109 1083 1118 1103 18 33.0 34.0 34.0 33.7 0.6

K075 1223 1217 1242 1227 13 30.0 31.0 30.0 30.3 0.6

K076 1391 1361 1391 1381 17 35.0 33.0 31.0 33.0 2.0

K077 1098 1096 1116 1103 11 29.0 29.0 29.0 29.0 0.0

K078 1394 1368 1354 1372 20 28.0 28.0 27.0 27.7 0.6

K079

K080 1100 1120 1110 1110 10 13.3 13.3 Individual Results

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg)

Thiamine Cl HCl
36

Lab A B C Avg SD A B C Avg SD

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg)

Thiamine Cl HCl

 Consensus Mean 1138 Consensus Mean 37.2

 Consensus Standard Deviation 145 Consensus Standard Deviation 36.3

 Maximum 2137 Maximum 351.7

 Minimum 884 Minimum 9.9

 N 41 N 25

 Consensus Mean 20.9

 Consensus Standard Deviation 10.2

 Maximum 40.0

 Minimum 9.9

 N 19

 Consensus Mean 286

 Consensus Standard Deviation 66

 Maximum 352

 Minimum 129

 N 6 Community Results Consensus Group A Consensus Group B
37

Table 8. Data summary table for vitamin B2 (riboflavin) in dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 1302 168 26.9 2.9

K001 1254 1291 1279 1275 19

K002

K003 1330 1370 1380 1360 26

K004 1466 1421 1268 1385 104

K006 1190 1190 1150 1177 23 12.5 12.1 10.3 11.6 1.2

K008 1117 1192 1156 1155 38 510.0 482.0 496.0 496.0 14.0

K009 1255 1219 1270 1248 26 256.1 199.0 205.4 220.2 31.3

K010

K011 1289 1310 1308 1302 12 31.3 31.6 31.1 31.3 0.3

K012

K013

K014 1420 1490 1400 1437 47

K015 1242 1291 1288 1274 27 49.4 34.3 47.0 43.5 8.1

K016

K018 1370 1370 50.0 50.0

K019

K020 1360 1360 1330 1350 17 227.0 233.0 232.0 230.7 3.2

K022 1283 1305 1317 1302 17 19.7 23.2 19.7 20.8 2.0

K024 4834 5313 5414 5187 310 224.0 64.6 87.4 125.3 86.2

K025 1410 1480 1470 1453 38 24.7 28.8 31.4 28.3 3.4

K026 1450 1520 1440 1470 44 24.0 23.9 24.6 24.2 0.4

K028 1590 1630 1590 1603 23 320.0 310.0 310.0 313.3 5.8

K029 1320 1290 1310 1307 15 15.2 15.2

K031 1350 1430 1350 1377 46 31.6 31.5 33.5 32.2 1.1

K032 1201 1227 1184 1204 22 25.0 29.1 23.5 25.9 2.9

K033 1100 1200 1100 1133 58 25.0 22.0 18.0 21.7 3.5

K034

K035 1212 1184 1153 1183 29

K036 1356 1261 1313 1310 48

K037 1370 1360 1370 1367 6

K040

K042 1430 1520 1620 1523 95

K043 1248 1263 1277 1263 15 24.1 25.5 28.4 26.0 2.2

K044 1300 1400 1400 1367 58 30.0 30.0 40.0 33.3 5.8

K045 1300 1300 1300 1300 0

K046 1597 1480 1504 1527 62 21.9 7.2 13.7 14.2 7.4

K047 1373 1429 1421 1408 30

K048

K049 1890 1790 1570 1750 164 27.0 21.0 27.0 25.0 3.5

K051 1290 1270 1320 1293 25 19.0 17.6 16.3 17.6 1.4

K056 1316 1342 1280 1313 31 27.3 22.4 20.4 23.4 3.6

K057 1208 1285 1283 1258 44 15.1 15.9 19.2 16.7 2.2

K058 1460 1500 1450 1470 26 24.6 23.7 25.2 24.5 0.8

K059 1243 1243 1248 1245 3 26.6 26.2 25.9 26.2 0.4

K062 1450 1440 1510 1467 38 24.0 25.0 28.0 25.7 2.1

K063 2030 2020 2020 2023 6

K064 1320 1200 1230 1250 62

K065 1594 1581 1609 1595 14

K066 1211 1169 1138 1173 36 27.6 23.0 21.8 24.1 3.1

K068

K069

K071 1250 1240 1190 1227 32

K073

K074 1447 1465 1483 1465 18 27.0 23.0 23.0 24.3 2.3

K075 1609 1562 1592 1588 24 40.0 41.0 36.0 39.0 2.6

K076 2007 1980 1984 1990 15 41.0 39.0 35.0 38.3 3.1

K077 1302 1365 1303 1323 36 25.0 25.0 22.0 24.0 1.7

K078 1796 1779 1744 1773 27 39.0 43.0 39.0 40.3 2.3

K079

K080 1310 1320 1300 1310 10 22.0 22.0

Riboflavin

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg) Individual Results
38

Lab A B C Avg SD A B C Avg SD

Riboflavin

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg)

 Consensus Mean 1372 Consensus Mean 30.4

 Consensus Standard Deviation 164 Consensus Standard Deviation 13.0

 Maximum 5187 Maximum 496.0

 Minimum 1133 Minimum 11.6

 N 46 N 30

 Consensus Mean 26.3

 Consensus Standard Deviation 8.9

 Maximum 50.0

 Minimum 11.6

 N 25

 Consensus Mean 277

 Consensus Standard Deviation 158

 Maximum 496

 Minimum 125

 N 5 Consensus Group A Consensus Group B Community Results
39

Table 9. Data summary table for vitamin B3 (niacinamide) in dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 13907 227 258 9

K001

K002

K003 15500 15500 15500 15500 0

K004 14521 14298 14346 14388 118

K006 13400 13100 13300 13267 153 163 192 173 176 15

K008 19000 19800 20000 19600 529 5394 5540 5500 5478 75

K009 15149 15036 15151 15112 66 31930 32186 31872 31996 167

K010

K011 14980 15301 15577 15286 299 298 294 296 296 2

K012

K013

K014 15100 14700 15100 14967 231 262 245 264 257 10

K015 13448 14121 13679 13749 342 752 376 256 461 259

K016

K018 18870 18870 290 290

K019

K020 15500 15600 15300 15467 153

K022 14375 14316 14312 14334 35 245 251 247 248 3

K024 14570 15059 14770 14800 246

K025 16600 16200 16200 16333 231 288 315 303 302 14

K026 14290 15000 14750 14680 360 250 248 15 171 135

K028 13808 13900 13850 13853 46 293 300 290 294 5

K029 14520 14380 14580 14493 103 217 217

K031 15000 14700 14800 14833 153 279 273 274 275 3

K032 15345 15149 15372 15289 121 275 276 297 283 12

K033

K034

K035 14883 15352 15202 15146 239

K036 16916 14916 14144 15325 1431

K037 15120 14660 14760 14847 242 240 230 210 227 15

K040

K042 13900 13900 14160 13987 150

K043

K044 14000 15000 15000 14667 577 1300 1200 1200 1233 58

K045 14000 14000 14000 14000 0 260 260 270 263 6

K046

K047 14211 14102 13956 14090 128

K048

K049 15000 15500 14900 15133 321 230 220 240 230 10

K051 15100 15200 15200 15167 58 268 252 248 256 10

K056 15035 14813 14720 14856 162 266 285 263 271 12

K057 3669 3834 3913 3805 124 238 269 268 258 18

K058 14500 14900 14600 14667 208 280 262 263 268 10

K059 14851 14826 14899 14859 37 439 469 458 455 15

K062 15100 15200 15400 15233 153 270 240 270 260 17

K063 22100 22400 21500 22000 458

K064 14300 12300 14200 13600 1127 250 300 265 272 26

K065 14333 14938 14432 14568 324

K066

K068

K069

K071 14710 14700 14640 14683 38 336 342 330 336 6

K073

K074 14799 15068 14838 14902 145 314 316 316 315 1

K075 15106 14734 14973 14938 189 287 277 283 282 5

K076 14700 14767 14953 14807 131 355 342 336 344 10

K077 14583 14564 14460 14536 66 259 271 260 263 7

K078 14832 14801 14693 14775 73 308 302 310 307 4

K079

K080 14950 14970 14860 14927 59 20 20

Niacinamide

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg) Individual Results
40

Lab A B C Avg SD A B C Avg SD

Niacinamide

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg)

 Consensus Mean 14770 Consensus Mean 290

 Consensus Standard Deviation 615 Consensus Standard Deviation 61

 Maximum 22000 Maximum 31996

 Minimum 3805 Minimum 20

 N 41 N 29

 Consensus Mean 273

 Consensus Standard Deviation 32

 Maximum 455

 Minimum 130

 N 25

 Consensus Mean 6051

 Consensus Standard Deviation 8669

 Maximum 31996

 Minimum 461

 N 4 Community Results Consensus Group A Consensus Group B
41

Figure 16. Thiamine hydrochloride in SRM 3280 Multivitamin/Multielement Tablets (data 

summary view – sample preparation 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 procedure employed. 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).
42

Figure 17. Thiamine hydrochloride in SRM 3252 Protein Drink Mix (data summary view –

sample preparation 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 procedure employed. The black solid lines represents the consensus means, and the 

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

each consensus mean. The gray shaded region represents the target zone for “acceptable” 

performance, which encompasses the NIST value determined by ID-LC-MS/MS from duplicate 

measurements of ten packets, bounded by an estimated uncertainty based on twice the method 

standard deviation.
43

Figure 18. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets (data summary view –

sample preparation 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 procedure employed. 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).
44

Figure 19. Riboflavin in SRM 3252 Protein Drink Mix (data summary view – sample preparation 

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 

procedure employed. The black solid lines represents the consensus means, and the black dotted 

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

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

encompasses the NIST value determined by ID-LC-MS/MS from duplicate measurements of ten 

packets, bounded by an estimated uncertainty based on twice the method standard deviation.
45

Figure 20. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets (data summary view –

sample preparation 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 procedure employed. 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).
46

Figure 21. Niacinamide in SRM 3252 Protein Drink Mix (data summary view – sample 

preparation 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 procedure employed. The black solid lines represents the consensus means, and the 

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

each consensus mean. The gray shaded region represents the target zone for “acceptable” 

performance, which encompasses the NIST value determined by ID-LC-MS/MS from duplicate 

measurements of ten packets, bounded by an estimated uncertainty based on twice the method 

standard deviation.
47

Figure 22. Thiamine hydrochloride in SRM 3280 Multivitamin/Multielement Tablets (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. 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).
48

Figure 23. Thiamine hydrochloride in SRM 3252 Protein Drink Mix (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. The black solid lines represents the consensus means, and the black dotted 

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

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

encompasses the NIST value determined by ID-LC-MS/MS from duplicate measurements of ten 

packets, bounded by an estimated uncertainty based on twice the method standard deviation.
49

Figure 24. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets (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. 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).
50

Figure 25. Riboflavin in SRM 3252 Protein Drink Mix (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. The black solid lines represents the consensus means, and the black dotted lines 

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

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

encompasses the NIST value determined by ID-LC-MS/MS from duplicate measurements of ten 

packets, bounded by an estimated uncertainty based on twice the method standard deviation.
51

Figure 26. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets (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. 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).
52

Figure 27. Niacinamide in SRM 3252 Protein Drink Mix (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. The black solid lines represents the consensus means, and the black dotted lines 

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

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

encompasses the NIST value determined by ID-LC-MS/MS from duplicate measurements of ten 

packets, bounded by an estimated uncertainty based on twice the method standard deviation.
53

Figure 28. Thiamine hydrochloride in SRM 3280 Multivitamin/Multielement Tablets (data 

summary view – calibration 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 

calibration approach employed. 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).
54

Figure 29. Thiamine hydrochloride in SRM 3252 Protein Drink Mix (data summary view –

calibration 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 calibration 

approach employed. The black solid lines represents the consensus means, and the black dotted 

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

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

encompasses the NIST value determined by ID-LC-MS/MS from duplicate measurements of ten 

packets, bounded by an estimated uncertainty based on twice the method standard deviation.
55

Figure 30. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets (data summary view –

calibration 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 calibration 

approach employed. 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).
56

Figure 31. Riboflavin in SRM 3252 Protein Drink Mix (data summary view – calibration 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 calibration approach employed. 

The black solid lines represents the consensus means, and the black dotted lines represent the 

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

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

NIST value determined by ID-LC-MS/MS from duplicate measurements of ten packets, bounded 

by an estimated uncertainty based on twice the method standard deviation.
57

Figure 32. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets (data summary view –

calibration 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 calibration 

approach employed. 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).
58

Figure 33. Niacinamide in SRM 3252 Protein Drink Mix (data summary view – calibration 

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 calibration approach

employed. The black solid lines represents the consensus means, and the black dotted lines 

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

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

encompasses the NIST value determined by ID-LC-MS/MS from duplicate measurements of ten 

packets, bounded by an estimated uncertainty based on twice the method standard deviation.
59

Figure 34. Thiamine HCl in SRM 3280 Multivitamin/Multielement Tablets and SRM 3252 

Protein Drink Mix (sample/sample comparison view). In this view, the individual laboratory 

results for one sample (SRM 3280) are compared to the results for another sample (SRM 3252). 

The solid red box represents the target zone for the control (x-axis) and unknown sample (y-axis). 

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

(y-axis).
60

Figure 35. Riboflavin in SRM 3280 Multivitamin/Multielement Tablets and SRM 3252 Protein 

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

one sample (SRM 3280) are compared to the results for another sample (SRM 3252). The solid 

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

dotted blue box represents the consensus zone for the control (x-axis) and the unknown sample (yaxis).
61

Figure 36. Niacinamide in SRM 3280 Multivitamin/Multielement Tablets and SRM 3252 Protein 

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

one sample (SRM 3280) are compared to the results for another sample (SRM 3252). The solid 

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

dotted blue box represents the consensus zone for the control (x-axis) and the unknown sample (yaxis).
62

VITAMIN K IN DIETARY SUPPLEMENTS

Study Overview

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

Multielement Tablets, and one NIST candidate SRM, SRM 3252 Protein Drink Mix. Participants 

were asked to use in-house analytical methods to determine the mass fraction of vitamin K1 in each 

of the matrices and report values on an as-received basis as phylloquinone.

Sample Information

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

multivitamin/multielement tablets. Before use, participants were instructed to grind all 30 tablets, 

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 

reported to participants prior to the study. The NIST certified value and uncertainty for vitamin 

K1 (phylloquinone) in SRM 3280 was determined by LC/MS following solvent extraction, in 

combination with data from numerous collaborating laboratories. The certified value and 

uncertainty are reported in the table below as phylloquinone on a dry-mass basis and after 

correction for moisture of the material (1.37 %).

Certified Mass Fraction

in SRM 3280 (mg/g)

Certified Mass Fraction

in SRM 3280 (mg/g)

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

Phylloquinone (K1) 22.8 ± 2.2 22.5 ± 2.2

Protein Powder. Participants were provided with one packet containing approximately 10 g of 

protein powder. A mixture of commercially available chocolate protein drink mix powders was 

blended and heat-sealed inside nitrogen-flushed 4-mil plastic bags, which were heat-sealed inside 

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

participants were instructed to thoroughly mix the contents of the packet, and a sample size of at 

least 0.5 g was recommended. 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 reported to participants prior to the study. 

Certified values are not available for this material at the time of the report.

Study Results

 Forty-eight laboratories enrolled in this exercise and received samples. Nineteen 

laboratories reported results for vitamin K in the multivitamin (40 % participation) and 6 

laboratories reported results for vitamin K in the protein powder (15 % participation).

 The consensus mean was within the target range for vitamin K in the multivitamin, but

with high variability (43 % RSD).

 The limited results reported for vitamin K in the protein powder were widely varied, with 

values ranging from 0.020 mg/kg to 1.555 mg/kg (128 % RSD).

 A majority of the laboratories reported using solvent extraction (79 %) as the sample 

preparation method. Some laboratories also reported using saponification (16 %). One 

laboratory did not report a sample preparation technique.
63

 A majority of the laboratories reported using LC-Abs (68 %) as their instrumental method 

for analysis. LC-Fluorescence (LC-FL) was also reported by some laboratories (21 %). 

Two laboratories did not report an analytical method.

 External standard was the most popular calibration approach (79 %), with some 

laboratories reporting using an internal standard calibration approach (11 %). Two

laboratories did not report the type of calibration method used.

Technical Recommendations 

The following recommendations are based on results obtained from the participants in this study. 

 Care should be taken to minimize losses during the extraction process, during solvent 

evaporation, and by carefully washing down container walls with several rinses during 

each step to ensure complete dissolution of any residues.

 In general, laboratories reporting more vigorous extraction procedures, i.e. those using 

hexanes and longer extraction times, reported results closer to the target value.

 Since loss by photodecomposition is possible, care should be taken to prevent such losses 

(use of amber vials, aluminum foil, and/or reduced lighting).

 When using LC-Abs, chromatographic coelutions may cause results to be biased high. This 

is particularly important if monitoring the absorbance in the UV where many other 

compounds may also have chromophores. To avoid a high bias, more selective detectors 

(fluorescence, mass spectrometry) or chromatography with alternate selectivity may be 

used.

 When making calibration solutions make sure they are of known quality. These may need 

to be tested before running samples, which may include determination of purity by 

chromatographic and spectroscopic methods.

 If using an internal standard, the internal standard must behave similarly to the analyte of 

interest in extraction, chromatographic analysis, and detection.
64

Table 10. Individualized data summary table (NIST) for vitamin K1 in dietary supplements.

Lab Code: NIST

Analyte Sample Units xi si Zcomm ZNIST N x* s* xNIST U 95

Vitamin K1 Multivitamin mg/kg 22.5 2.2 0.3 0.0 19 20.1 8.7 22.5 2.2

Vitamin K1 Protein Drink mg/kg 6 0.6 0.7

xi Mean of reported values N Number of quantitative xNIST NIST-assessed value

si Standard deviation of reported values values reported U 95 ±95% confidence interval

Zcomm Z-score with respect to community x* Robust mean of reported about the assessed value or

 consensus values standard deviation (sNIST)

ZNIST Z-score with respect to NIST value s* Robust standard deviation

Exercise K - February 2014 - Vitamin K

1. Your Results 2. Community Results 3. Target

National Institute of Standards & Technology
65

Table 11. Data summary table for vitamin K1 in dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 22.5 2.2

K001

K002

K003 70.3 71.2 55.2 65.6 9.0

K006

K010

K014 21.3 21.4 21.2 21.3 0.1

K016

K017

K019

K020 27.5 23.0 24.0 24.8 2.4 0.049 0.088 0.042 0.060 0.025

K024 17.2 16.3 14.0 15.8 1.6

K025 0.4 0.5 0.5 0.5 0.0 0.950 0.986 0.935 0.957 0.026

K026 24.8 24.6 24.4 24.6 0.2 0.027 0.026 0.028 0.027 0.001

K028

K029 21.6 20.5 19.5 20.5 1.1 0.022 0.023 0.023 0.001

K031 22.0 21.7 22.3 22.0 0.3

K033 20.0 21.0 21.0 20.7 0.6 0.020 0.020

K034

K035 18.3 17.9 18.7 18.3 0.4

K037 8.0 7.0 6.0 7.0 1.0 0.800 0.800 0.600 0.733 0.115

K040

K042

K043

K045

K046 19.6 22.4 20.1 20.7 1.5

K047

K048

K049 98.0 99.3 99.6 99.0 0.9

K051 21.0 18.6 20.9 20.2 1.4

K056

K057 13.3 12.3 9.2 11.6 2.2

K058 11.9 12.9 11.7 12.1 0.7

K059 31.4 30.9 34.8 32.4 2.1

K062 20.6 18.9 23.7 21.1 2.4

K063

K064

K065 15.5 16.1 15.7 15.8 0.3 1.661 1.563 1.441 1.555 0.110

K066

K068

K069

K071

K073

K074

K075

K076

K077

K078

K079

 Consensus Mean 20.1 Consensus Mean 0.559

 Consensus Standard Deviation 8.7 Consensus Standard Deviation 0.717

 Maximum 99.0 Maximum 1.555

 Minimum 0.5 Minimum 0.020

 N 19 N 6 Community Results Individual Results

Phylloquinone

SRM 3280 Multivitamin/Multielement Tablets (mg/kg) SRM 3252 Protein Drink Mix (mg/kg)
66

Figure 37. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets (data summary view

– sample preparation 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 procedure employed. 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 38. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets (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. 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 39. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets (data summary view 

– calibration 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 calibration 

approach employed. 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 40. Phylloquinone in SRM 3252 Protein Drink Mix (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.
70

Figure 41. Phylloquinone in SRM 3280 Multivitamin/Multielement Tablets and SRM 3252 

Protein Drink Mix (sample/sample comparison view). In this view, the individual laboratory 

results for one sample (SRM 3280) are compared to the results for a second sample (SRM 3252). 

The solid red box represents the target zone for the control (x-axis). The dotted blue lines

represents the bounds of the consensus zone for the control (x-axis).
71

ACRYLAMIDE IN CHOCOLATE AND COFFEE

Study Overview

In this study, participants were provided with one NIST SRM, SRM 2384 Baking Chocolate, and 

a sample of whole roasted coffee beans. Participants were asked to use in-house analytical 

methods to determine the mass fraction of acrylamide in each of the matrices and report values on 

an as-received basis.

Sample Information

Baking Chocolate. Participants were provided with one bar containing 91 g of baking chocolate 

prepared from 100 % cocoa beans from a single production lot. Participants were instructed to use 

a sample size of at least 10 g. Participants were asked to store the material under controlled room 

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

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

NIST reference value and uncertainty for acrylamide, determined by collaborating laboratories, 

are provided in the table below.

Analyte

Reference Mass Fraction 

in SRM 2384 (ng/g)

Acrylamide 138 ± 17

Coffee. Participants were provided with one packet containing 100 g of roasted coffee beans. 

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

and a sample size of at least 5 g was recommended. Participants were asked to store the material 

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

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

participants prior to the study. The NIST target value for acrylamide determined by collaborating 

laboratories, and uncertainty (estimated as twice the standard deviation from 5 laboratories), are 

provided in the table below.

Analyte

Estimated Mass Fraction 

in Roasted Coffee Beans (ng/g)

Acrylamide 141 ± 9

Study Results

 Nine laboratories enrolled in this exercise and received samples. Four laboratories reported 

results for acrylamide in the chocolate (44 % participation), and three laboratories reported 

results for acrylamide in the coffee (33 % participation).

 Limited conclusions can be drawn about the quality of the collaborative data from this 

study because very few laboratories returned results.

 The consensus mean for acrylamide was within the target range for the chocolate 

sample, but with very high variability (111 % RSD).

 The consensus mean for acrylamide was below the target range for the coffee sample, 

with high variability (46 % RSD).
72

 Two of the four laboratories reported using derivatization following sample extraction (50 

%). One laboratory reported using only solvent extraction (25 %), and one laboratory 

reported using QuEChERS for sample cleanup (25 %).

 Two laboratories reported using gas chromatography with mass spectrometric detection 

(GC-MS) as their analytical method for analysis (50 %), and two laboratories reported 

using LC-MS or LC-MS/MS (50 %).

 Two laboratories reported using an external standard approach to quantitation (50 %), and 

two laboratories reported using an internal standard approach (50 %).

Technical Recommendations

The following recommendations are based on results obtained from the participants in this study. 

 Because the data for this study was very limited (only 3 or 4 laboratories reporting data), 

drawing extensive technical conclusions is difficult. Similarly, the high level of betweenlaboratory variability may be exaggerated as a result of the low number of participants.

 No trends were identified indicating that any particular sample preparation method or 

instrumental technique provided more accurate results than another.
73

Table 12. Individualized data summary table (NIST) for acrylamide in chocolate and coffee.

Lab Code: NIST

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

Acrylamide Chocolate ng/g 138 17 0.0 0.0 4 142 157 138 17

Acrylamide Coffee ng/g 141 9 1.0 0.0 3 96 45 141 9

xi Mean of reported values N Number of quantitative xNIST NIST-assessed value

si Standard deviation of reported values values reported U 95 ±95% confidence interval

Zcomm Z-score with respect to community x* Robust mean of reported about the assessed value or

 consensus values standard deviation (sNIST)

ZNIST Z-score with respect to NIST value s* Robust standard deviation

Exercise K - February 2014 - Acrylamide

1. Your Results 2. Community Results 3. Target

National Institute of Standards & Technology
74

Table 13. Data summary table for acrylamide in chocolate and coffee.

Lab A B C Avg SD A B C Avg SD

NIST 138 17 141 9

K002

K003 34 38 39 37 3

K010

K024 140 121 123 128 10 54 50 56 53 3

K040

K048 339 343 341 341 2 107 104 103 105 2

K055

K061

K062 60 63 59 61 2 131 132 129 131 2

 Consensus Mean 142 Consensus Mean 96

 Consensus Standard Deviation 157 Consensus Standard Deviation 45

 Maximum 341 Maximum 131

 Minimum 37 Minimum 53

 N 4 N 3

SRM 2384 Baking Chocolate (ng/g) Individual Results Community ResultsCoffee (ng/g)

Acrylamide
75

Figure 42. Acrylamide in SRM 2384 Baking Chocolate (data summary view – sample preparation 

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 

method employed. 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 bounded by twice its uncertainty (U95).
76

Figure 43. Acrylamide in SRM 2384 Baking Chocolate (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. 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 bounded by twice its uncertainty (U95).
77

Figure 44. Acrylamide in SRM 2384 Baking Chocolate (data summary view – calibration

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 calibration approach

employed. 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 bounded by twice its uncertainty (U95).
78

Figure 45. Acrylamide in roasted coffee beans (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 estimated 

value (based on data from 5 collaborating laboratories) bounded by twice its uncertainty (twice the 

standard deviation of the data from collaborating laboratories).
79

Figure 46. Acrylamide in SRM 2384 Baking Chocolate and roasted coffee beans (sample/sample 

comparison view). In this view, the individual laboratory results for one sample (SRM 2384) are 

compared to the results for a second sample (roasted coffee beans). The solid red box represents 

the target zone for the control (x-axis). The dotted blue box represents the consensus zone for the 

control (x-axis) and the unknown sample (y-axis).
80

PHYTOSTEROLS IN SAW PALMETTO

Study Overview

In this study, participants were provided with two NIST SRMs, SRM 3250 Serenoa repens Fruit 

and SRM 3251 Serenoa repens Extract. Participants were asked to use in-house analytical 

methods to determine the mass fractions of phytosterols (campesterol, β-sitosterol, and 

stigmasterol) in each of the matrices and report values on an as-received basis.

Sample Information

Saw Palmetto Fruit. Participants were provided with one packet containing 6 g of Serenoa repens

(saw palmetto) berries that had been freeze-dried, ground, and heat-sealed inside nitrogen-flushed 

4-mil polyethylene bags, which were then sealed inside aluminized plastic bags with 2 packets of 

silica gel. Before use, participants were instructed to mix each packet thoroughly and a sample 

size of at least 0.5 g was recommended. Participants were asked to store the material at room 

temperature, 10 °C to 30 °C, and to prepare three samples, and report three measurements of each 

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

participants prior to the study. The NIST certified values and uncertainties for phytosterols in 

SRM 3250 were determined using LC-MS following solvent extraction and basic hydrolysis, and 

by gas chromatography with flame ionization detection (GC-FID) following solvent extraction, 

basic hydrolysis, and derivatization. The values and uncertainties are reported in the table below 

both on a dry-mass basis and after correction for moisture of the material (6.42 %).

Analyte

Certified Mass Fraction

in SRM 3250 (mg/g)

(dry-mass basis)

Certified Mass Fraction

in SRM 3250 (mg/g)

(as-received basis)

Campesterol 0.1175 ± 0.0025 0.1100 ± 0.0023

β-sitosterol 0.454 ± 0.018 0.425 ± 0.017

Stigmasterol 0.0477 ± 0.0020 0.0446 ± 0.0019

Saw Palmetto Extract. Participants were provided with three ampoules, each containing 1 mL of 

a carbon dioxide extract of Serenoa repens (saw palmetto) berries. Before use, participants were 

instructed to mix each ampoule thoroughly and a sample size of at least 125 mg was recommended. 

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

one sample and report one measurement of each analyte from each ampoule provided. 

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

values and uncertainties for phytosterols in SRM 3251 were determined using LC-MS following 

solvent extraction and basic hydrolysis, and by GC-FID following solvent extraction, basic 

hydrolysis, and derivatization; the values and uncertainties are reported in the table below.
81

Analyte

Certified Mass Fraction

in SRM 3251 (mg/g)

(as-received basis)

Campesterol 0.533 ± 0.031

β-sitosterol 1.666 ± 0.064

Stigmasterol 0.247 ± 0.040

Study Results

 Twenty-six laboratories enrolled in this exercise and received samples. Ten laboratories 

reported data for phytosterols in the saw palmetto fruit (39 % participation), and eleven 

laboratories reported data for phytosterols in the saw palmetto extract (42 % participation).

 The consensus means were within the target ranges with acceptable between-laboratory 

variability for all three phytosterols in the saw palmetto extract (less than 15 % RSD for 

all analytes).

 The consensus mean for stigmasterol in the saw palmetto fruit was equivalent to the 

minimum of the target range, but the between-laboratory variability was high (30 % RSD).

 The consensus means were below the target ranges for campesterol and β–sitosterol in the 

saw palmetto fruit with acceptable between-laboratory variability (18 % and 12 % RSD, 

respectively).

 Laboratories reported using either solvent extraction with hydrolysis (37 %) or solvent 

extraction with hydrolysis and derivatization (55 %) as the sample preparation method. 

One laboratory did not report a sample preparation technique.

 A majority of the laboratories reported using GC-FID (82 %) for phytosterols 

determination. One laboratory reported using GC-MS (9 %) as their instrumental method, 

and one laboratory did not report the type of analytical method used.

 Laboratories reported using both external standard and internal standard approaches to 

quantitation of phytosterols (36 % and 55 %, respectively). One laboratory did not report 

the calibration approach used.

Technical Recommendations

The following recommendations are based on results obtained from the participants in this study. 

 The low results for campesterol and β–sitosterol in the saw palmetto fruit are consistent 

with the results from Exercise H, conducted in 2012 (Figure 68 and Figure 69). More 

details on Exercise H can be found in the final report, available at 

http://dx.doi.org/10.6028/NIST.IR.7903.

 As shown in Figure 68 and Figure 69, the consensus means from Exercise H and 

Exercise K are nearly identical. Between-laboratory precision has improved for both 

analytes. For both analytes in both exercises, the consensus means are below the target 

ranges.

 The low results could be caused by incomplete extraction of these phytosterols from 

the saw palmetto berry matrix. All commercial saw palmetto products are sold as 

extracts, so laboratory protocols may not be developed to fully extract phytosterols 

from the plant material. In addition, many methods for phytosterols that involve the 

use of an internal standard suggest its addition after the extraction steps are complete. 

Addition of the internal standard this late will not compensate for extraction 
82

inefficiencies. 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).

 The low results could also indicate instability of these analytes in this matrix. NIST 

will investigate this possible instability further.

 A slight calibration error is apparent in the sample/sample comparison graphs. Calibrant 

materials should be subjected to the same preparation procedure as the samples 

(derivatization, hydrolysis, etc.) to avoid calibration bias.
83

Table 14. Individualized data summary table (NIST) for phytosterols in saw palmetto dietary supplements.

Lab Code: NIST

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

Campesterol SP Fruit mg/g 0.110 0.002 1.8 0.0 10 0.083 0.015 0.110 0.002

Campesterol SP Extract mg/g 0.533 0.031 -0.4 0.0 11 0.568 0.078 0.533 0.031

b-sitosterol SP Fruit mg/g 0.425 0.017 4.0 0.0 10 0.285 0.035 0.425 0.017

b-sitosterol SP Extract mg/g 1.67 0.06 0.4 0.0 11 1.60 0.16 1.67 0.06

Stigmasterol SP Fruit mg/g 0.0446 0.0019 0.3 0.0 10 0.0410 0.0123 0.0446 0.0019

Stigmasterol SP Extract mg/g 0.247 0.040 -0.2 0.0 11 0.254 0.038 0.247 0.040

xi Mean of reported values N Number of quantitative xNIST NIST-assessed value

si Standard deviation of reported values values reported U95 ±95% confidence interval

Zcomm Z-score with respect to community x* Robust mean of reported about the assessed value or

 consensus values standard deviation (sNIST)

ZNIST Z-score with respect to NIST value s* Robust standard deviation

Exercise K - February 2014 - Phytosterols

1. Your Results 2. Community Results 3. Target

National Institute of Standards & Technology
84

Table 15. Data summary table for campesterol in saw palmetto dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 0.1100 0.0020 0.533 0.031

K002

K006

K008

K009 0.0904 0.0841 0.0842 0.0862 0.0036 0.576 0.574 0.538 0.563 0.021

K010

K012 0.0850 0.0822 0.0816 0.0829 0.0018 0.571 0.568 0.547 0.562 0.013

K014

K015

K017

K019

K021

K024 0.0520 0.0634 0.0820 0.0658 0.0151 0.362 0.339 0.324 0.342 0.019

K031 0.0850 0.0900 0.0900 0.0883 0.0029 0.612 0.610 0.600 0.607 0.006

K040

K043 0.0810 0.0840 0.0800 0.0817 0.0021 0.650 0.645 0.639 0.645 0.006

K044 0.1100 0.1100 0.1100 0.1100 0.0000 0.720 0.730 0.700 0.717 0.015

K045

K053 0.0452 0.0316 0.0420 0.0396 0.0071 0.685 0.700 0.512 0.632 0.104

K055

K057 0.0910 0.1087 0.0909 0.0969 0.0102 0.538 0.523 0.517 0.526 0.011

K059 0.504 0.499 0.511 0.505 0.006

K062

K064 0.0771 0.0777 0.0774 0.0004 0.525 0.524 0.522 0.524 0.001

K066 0.0810 0.0813 0.0812 0.0812 0.0002 0.537 0.541 0.557 0.545 0.011

K067

K070

 Consensus Mean 0.0826 Consensus Mean 0.568

 Consensus Standard Deviation 0.0145 Consensus Standard Deviation 0.078

 Maximum 0.1100 Maximum 0.717

 Minimum 0.0396 Minimum 0.342

 N 10 N 11 Community Results

Campesterol Individual Results

SRM 3250 Saw Palmetto Fruit (mg/g) SRM 3251 Saw Palmetto Extract (mg/g)
85

Table 16. Data summary table for β–sitosterol in saw palmetto dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 0.425 0.017 1.67 0.06

K002

K006

K008

K009 0.334 0.320 0.310 0.321 0.012 1.74 1.72 1.61 1.69 0.07

K010

K012 0.291 0.287 0.294 0.290 0.003 1.69 1.68 1.64 1.67 0.03

K014

K015

K017

K019

K021

K024 0.272 0.323 0.302 0.299 0.026 1.53 1.42 1.38 1.44 0.08

K031 0.296 0.318 0.315 0.310 0.012 1.84 1.81 1.73 1.79 0.06

K040

K043 0.225 0.226 0.223 0.225 0.002 1.29 1.28 1.23 1.27 0.03

K044 0.300 0.300 0.310 0.303 0.006 1.81 1.82 1.70 1.78 0.07

K045

K053 0.203 0.147 0.188 0.179 0.029 1.64 1.66 1.19 1.50 0.26

K055

K057 0.295 0.328 0.295 0.306 0.019 1.52 1.52 1.48 1.50 0.02

K059 1.62 1.62 1.64 1.63 0.01

K062

K064 0.277 0.277 0.277 0.000 1.70 1.71 1.71 1.71 0.01

K066 0.271 0.282 0.275 0.276 0.006 1.55 1.55 1.57 1.56 0.01

K067

K070

 Consensus Mean 0.285 Consensus Mean 1.60

 Consensus Standard Deviation 0.035 Consensus Standard Deviation 0.16

 Maximum 0.321 Maximum 1.79

 Minimum 0.179 Minimum 1.27

 N 10 N 11

b-sitosterol

SRM 3250 Saw Palmetto Fruit (mg/g) SRM 3251 Saw Palmetto Extract (mg/g) Individual Results Community Results
86

Table 17. Data summary table for stigmasterol in saw palmetto dietary supplements.

Lab A B C Avg SD A B C Avg SD

NIST 0.0446 0.0019 0.247 0.040

K002

K006

K008

K009 0.0669 0.0591 0.0594 0.0618 0.0044 0.390 0.388 0.402 0.393 0.008

K010

K012 0.0342 0.0339 0.0351 0.0344 0.0006 0.253 0.261 0.243 0.252 0.009

K014

K015

K017

K019

K021

K024 0.0345 0.0426 0.0383 0.0385 0.0041 0.257 0.262 0.217 0.245 0.025

K031 0.0470 0.0520 0.0510 0.0500 0.0026 0.298 0.296 0.288 0.294 0.005

K040

K043 0.0291 0.0266 0.0268 0.0275 0.0014 0.168 0.160 0.153 0.160 0.008

K044 0.0400 0.0400 0.0400 0.0400 0.0000 0.290 0.290 0.270 0.283 0.012

K045

K053 0.0396 0.0244 0.0434 0.0358 0.0101 0.253 0.270 0.197 0.240 0.038

K055

K057 0.0546 0.0669 0.0501 0.0572 0.0087 0.287 0.269 0.266 0.274 0.011

K059 0.245 0.235 0.215 0.232 0.015

K062

K064 0.0319 0.0320 0.0320 0.0001 0.234 0.229 0.229 0.231 0.003

K066 0.0370 0.0358 0.0341 0.0356 0.0015 0.235 0.224 0.235 0.231 0.006

K067

K070

 Consensus Mean 0.0410 Consensus Mean 0.254

 Consensus Standard Deviation 0.0123 Consensus Standard Deviation 0.037

 Maximum 0.0618 Maximum 0.393

 Minimum 0.0275 Minimum 0.160

 N 10 N 11

Stigmasterol

SRM 3250 Saw Palmetto Fruit (mg/g) SRM 3251 Saw Palmetto Extract (mg/g) Individual Results Community Results
87

Figure 47. Campesterol in SRM 3250 Serenoa repens Fruit (data summary view – sample

preparation 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 method employed. The black solid lines represent the consensus means for each 

sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. 

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

encompasses the NIST certified value bounded by twice its uncertainty (U95).
88

Figure 48. Campesterol in SRM 3251 Serenoa repens Extract (data summary view – sample 

preparation 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 method employed. The black solid lines represent the consensus means for each 

sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. 

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

encompasses the NIST certified value bounded by twice its uncertainty (U95).
89

Figure 49. β-sitosterol in SRM 3250 Serenoa repens Fruit (data summary view – sample 

preparation 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 method employed. The black solid lines represent the consensus means for each 

sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. 

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

encompasses the NIST certified value bounded by twice its uncertainty (U95).
90

Figure 50. β-sitosterol in SRM 3251 Serenoa repens Extract (data summary view – sample 

preparation 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 method employed. The black solid lines represent the consensus means for each 

sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. 

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

encompasses the NIST certified value bounded by twice its uncertainty (U95).
91

Figure 51. Stigmasterol in SRM 3250 Serenoa repens Fruit (data summary view – sample 

preparation 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 method employed. The black solid lines represent the consensus means for each 

sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. 

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

encompasses the NIST certified value bounded by twice its uncertainty (U95).
92

Figure 52. Stigmasterol in SRM 3251 Serenoa repens Extract (data summary view – sample 

preparation 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 method employed. The black solid lines represent the consensus means for each 

sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. 

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

encompasses the NIST certified value bounded by twice its uncertainty (U95).
93

Figure 53. Campesterol in SRM 3250 Serenoa repens Fruit (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. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
94

Figure 54. Campesterol in SRM 3251 Serenoa repens Extract (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. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
95

Figure 55. β-sitosterol in SRM 3250 Serenoa repens Fruit (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. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
96

Figure 56. β-sitosterol in SRM 3251 Serenoa repens Extract (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. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
97

Figure 57. Stigmasterol in SRM 3250 Serenoa repens Fruit (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. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
98

Figure 58. Stigmasterol in SRM 3251 Serenoa repens Extract (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. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
99

Figure 59. Campesterol in SRM 3250 Serenoa repens Fruit (data summary view – calibration 

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

standard deviation (error bars). The color of the data point represents the calibration approach

employed. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
100

Figure 60. Campesterol in SRM 3251 Serenoa repens Extract (data summary view – calibration 

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

standard deviation (error bars). The color of the data point represents the calibration approach 

employed. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
101

Figure 61. β-sitosterol in SRM 3250 Serenoa repens Fruit (data summary view – calibration 

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

standard deviation (error bars). The color of the data point represents the calibration approach 

employed. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
102

Figure 62. β-sitosterol in SRM 3251 Serenoa repens Extract (data summary view – calibration 

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

standard deviation (error bars). The color of the data point represents the calibration approach 

employed. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
103

Figure 63. Stigmasterol in SRM 3250 Serenoa repens Fruit (data summary view – calibration 

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

standard deviation (error bars). The color of the data point represents the calibration approach 

employed. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
104

Figure 64. Stigmasterol in SRM 3251 Serenoa repens Extract (data summary view – calibration 

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

standard deviation (error bars). The color of the data point represents the calibration approach 

employed. The black solid lines represent the consensus means for each sample preparation 

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

deviation about the consensus mean for that sample preparation method. The gray shaded region 

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

value bounded by twice its uncertainty (U95).
105

Figure 65. Campesterol in SRM 3250 Serenoa repens Fruit and SRM 3251 Serenoa repens

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

sample (SRM 3250) are compared to the results for a second sample (SRM 3251). The solid red 

box represents the target zone for the control (x-axis) and unknown sample (y-axis). The dotted 

blue box represents the consensus zone for the control (x-axis) and the unknown sample (y-axis).
106

Figure 66. β-sitosterol in SRM 3250 Serenoa repens Fruit and SRM 3251 Serenoa repens Extract 

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

(SRM 3250) are compared to the results for a second sample (SRM 3251). The solid red box 

represents the target zone for the control (x-axis) and unknown sample (y-axis). The dotted blue 

box represents the consensus zone for the control (x-axis) and the unknown sample (y-axis).
107

Figure 67. Stigmasterol in SRM 3250 Serenoa repens Fruit and SRM 3251 Serenoa repens

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

sample (SRM 3250) are compared to the results for a second sample (SRM 3251). The solid red 

box represents the target zone for the control (x-axis) and unknown sample (y-axis). The dotted 

blue box represents the consensus zone for the control (x-axis) and the unknown sample (y-axis).
108

 

Figure 68. Comparison of results for campesterol in SRM 3250 Saw Palmetto Fruit from Exercise H (left) and Exercise K (right). In 

both graphs, individual laboratory data are plotted with the individual laboratory standard deviation (error bars). The black solid lines 

represent the consensus means for each sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. The gray shaded region represents 

the target zone for “acceptable” performance, which encompasses the NIST certified value bounded by twice its uncertainty (U95). 

NOTE: The participant laboratory numbers are changed for each exercise, so no correlation can be made between laboratory numbers 

from Exercise H and Exercise K.
109

 

Figure 69. Comparison of results for β-sitosterol in SRM 3250 Saw Palmetto Fruit from Exercise H (left) and Exercise K (right). In 

both graphs, individual laboratory data are plotted with the individual laboratory standard deviation (error bars). The black solid lines 

represent the consensus means for each sample preparation method, and the black dotted lines represent the consensus variability 

calculated as one standard deviation about the consensus mean for that sample preparation method. The gray shaded region represents 

the target zone for “acceptable” performance, which encompasses the NIST certified value bounded by twice its uncertainty (U95). 

NOTE: The participant laboratory numbers are changed for each exercise, so no correlation can be made between laboratory numbers 

from Exercise H and Exercise K.