July 28, 2008 

Dear Colleague: 

Enclosed is your “Participation Certificate” for the Spring 2008 Dietary Supplement 

Quality Assurance Program (DSQAP) exercise. This certificate displays your results 

relative to the distribution of results reported by all participants. In addition, a one-page 

summary of individual, community, and NIST results has been included. 

The individual data reports are listed for each analyte separately and are organized into 

three sections: 1) the individual laboratory/participant’s results, 2) the overall community 

results, and 3) the NIST-assessed value and associated uncertainty. For your individual 

results, the mean and overall standard deviation are listed for each analyte for which a 

dataset was received. Since single measurements were made for each of three distributed 

unknown samples (Packets A, B, and C) during this Round B exercise, the overall 

standard deviation (stotal) is comprised of only the between-sample standard deviation 

(sbetween) component. A measure of how comparable the individual 

laboratory/participant’s result is to the overall community’s performance for each analyte 

is represented as a Z-score. This is determined as the difference between your individual 

result and the median of the community result divided by the MADe (a robust estimate of 

the standard deviation derived from the median absolute deviation (MAD)) of the 

community result. The significance of the Z-score is as followed: |Z| < 2 is considered 

within the consensus value of the community result, 2 < |Z| < 3 is considered as 

marginally different from the consensus value of the community result, and |Z| > 3 is 

considered as significantly different from the consensus value of the community result. 

With the exception of sterols, a sufficient number of laboratories reported results for 

meaningful statistical analysis (N>8). Although statistical analysis is limited by lower 

participation for the determination of sterols, this study appears to indicate that methods 

of analysis need improvement. Is this an exercise that should be repeated since it appears 

to be problematic? Are there other analytes from this exercise or the pilot that you would 

like to see repeated? 

The results of this exercise and materials for future exercises will be discussed during an 

informal half-day workshop at the AOAC meeting in Dallas. The workshop will be from 

9-12 on Tuesday, September 23, 2008 in Cumberland J. It will be followed by a 

Technical Division on Reference Materials sponsored symposium, “Proficiency Testing 

and Reference Materials: Interrelations and Opportunities”. If you would like to attend, 

you must register for the AOAC meeting, 
http://www.aoac.org/meetings1/122nd_annual_mtg/main.htm. In addition, please e-mail 

DSQAP@nist.gov by September 2, 2008 if you plan to attend the workshop. 

We appreciate your participation in this exercise. If you have any questions regarding the 

certificate or summary sheet please e-mail them to DSQAP@nist.gov. We would like to 

hear feedback on your needs for this program, please let us know what analytes/matricies 

are most useful. 

We hope to see you in September. 

Sincerely, 

Catherine Rimmer, Ph.D. Laura Wood Katrice Lippa, Ph.D. 

Research Chemist Biologist Research Chemist 

DSQAP Coordinator 

(organic analytes) 

DSQAP Coordinator 

(inorganic analytes) 

DSQAP Data Analyst 
Analyte Units Mean s within s between s total Z sig N Median MADe Min 

Arsenic mg/kg 0.265 correction 1.000 0.2 13 0.257 0.035 0.201 0

Synephrine mg/g 9.10 correction 1.00 1.8 8 8.46 0.36 4.77 

Campesterol mg/g 0.118 correction 1.000 6.4 ** 5 0.084 0.005 0.080 0

Bsitosterol mg/g 0.454 correction 1.000 59.4 ** 5 0.293 0.003 0.249 0

Stigmasterol mg/g 0.048 correction 1.000 0.8 5 0.044 0.004 0.041 0

Quercetin mg/g 7.56 correction 1.00 -0.6 14 8.02 0.71 7.06 2

Kaempferol mg/g 7.19 correction 1.00 0.8 14 6.79 0.52 6.29 2

Isorhamnetin mg/g 1.90 correction 1.00 0.8 13 1.77 0.17 0.15 

VitaminB1 mg/g 1.05 correction 1.00 0.2 21 1.01 0.25 0.63 VitaminB2 mg/g 1.27 correction 1.00 -0.1 21 1.29 0.20 0.91 

Mean Average of all your reported values N Number of quantitati

s within Pooled within-sample standard deviation (repeatability) Median Median of the report

s between Between-sample standard deviation, adjusted for s within MADe Median Absolute De

s total Overall standard deviation (combines s within and s between) Min, Max Minimum and maxim

Z Z-score: (Mean - Median)/MADe Value NIST-assessed valu

sig Approximate significance of Z: U 95 ±95% confidence int

 (blank) = within consensus value * = marginally different from consensus value ** = significantly different from consensus value

1. Your Results, Lab Code: NIST 

National Institute of Standards and Technology

Analytical Chemistry Division

2. Community Results
National Institute of Standards and Technology

Dietary Supplements Quality Assurance Program

Participated in the May 2008 Interlaboratory Comparability Study

Chief, Analytical Chemistry Division

NIST

Analytical Chemistry Division

National Institute of Standards and Technology

DSQAP Coordinator DSQAP Coordinator DSQAP Data Analyst Arsenic Synephrine Campesterol Bsitosterol Stigmasterol Quercetin Kaempferol Isorhamnetin VitaminB1 VitaminB2

10-4

10-3

10-2

Mass Fraction

Interquartile

range

Number

of data

Your

value
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3242 A1 B1 C1 Mean s total 

B101 0.86 0.21 0.2 0.2 0.20 0.00B104 0.99 0.23 0.23 0.24 0.23 0.01B105 1.07 0.3 0.27 0.29 0.29 0.01B107 1.06 0.24 0.26 0.26 0.26 0.01B111 1.23 0.33 0.33 0.34 0.33 0.00B114 0.95 0.23 0.23 0.23 0.23B117 1.25 0.31 0.33 0.32 0.32 0.01B119 0.98 0.26 0.27 0.24 0.26 0.02B122 1.04 0.25 0.26 0.26 0.26 0.01B123 1.12 0.28 0.27 0.24 0.26 0.02B124 1.09 0.24 0.22 0.27 0.24 0.02B126 0.99 0.28 0.26 0.27 0.27 0.01B127 1.04 0.22 0.23 0.23 0.23 0.00

13 13

1.05 0.26 0.011.04 0.260.08 0.04

7.8 13.7 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

1.0 0.3 Consensus box encloses ±2×MADe around consensus medians.0.0 0.0 Plot encloses ±40 % around consensus medians.

Unknown: SRM 3240

±U 95

MADe

Median

Mean

Arsenic, mg/kg

N

%RSD

NIST

B127

B126

B124

B123

B122 B119

B117

B114

B111

B107

B105

B104

B101

NISTConsensus

Arsenic in Control (SRM 3242), mg/kg

Arsenic in Unknown (SRM 3240), mg/kg
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3259 A1 B1 C1 Mean s total 

B103 73.6 4.7 5. 4.6 4.77 0.21B106 68.2 7.99 8.01 8.05 8.02 0.03B110 66.3 7.51 7.1 7.08 7.23 0.24B113 67.2 8.45 8.49 8.6 8.51 0.08B124 65. 8.24 8.62 8.48 8.45 0.19B126 67.21 8.43 8.43 8.56 8.47 0.08B127 69.64 8.62 8.67 8.58 8.62 0.05B128 70.82 8.75 8.75 8.85 8.78 0.06

8 8

68.50 7.86 0.1467.71 8.46

2.48 0.36

3.7 4.2 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

71.9 9.1 Consensus box encloses ±2×MADe around consensus medians.

1.2 0.1 Plot encloses ±25 % around consensus medians.

Synephrine, mg/g

N

%RSD

NIST

±U 95

MADe

Median

Mean

Unknown: SRM 3258

B128

B127

B124 B126 B113

B110

B106

B103

55 60 65 70 75 8

10987

NISTConsensus

Synephrine in Control (SRM 3259), mg/g

Synephrine in Unknown (SRM 3258), mg/g
Dietary Supplements Quality Assurance Program

May 2008 Study - Round B

Control

Lab SRM 3251 A1 B1 C1 Mean s total 

B106 0.69 0.14 0.13 0.15 0.14 0.012B111 0.5 0.08 0.08 0.08 0.08 0.004B113 0.61 0.14 0.14 0.12 0.13 0.008B119 0.48 0.09 0.07 0.08 0.08 0.012B126 0.6 0.08 0.09 0.09 0.08 0.007

5 5

0.58 0.10 0.010.60 0.080.13 0.0122.1 6.4 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

0.53 0.12 Consensus box encloses ±2×MADe around consensus medians.0.02 0.00 Plot encloses ±80 % around consensus medians.

Unknown: SRM 3250

±U 95

MADe

Median

Mean

Campesterol, mg/g

N

%RSD

NIST

B126

B119

B113

B111

B106

0.3 0.5 0.7 0.9

0.13 0.1 0.07 0.04

NISTConsensus

Campesterol in Control (SRM 3251), mg

Campesterol in Unknown (SRM 3250), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3251 A1 B1 C1 Mean s total 

B106 1.92 0.48 0.44 0.47 0.46 0.02B111 1.73 0.3 0.29 0.29 0.29 0.00B113 1.43 0.29 0.29 0.29 0.29 0.00B119 1.44 0.27 0.23 0.25 0.25 0.02B126 1.95 0.28 0.3 0.3 0.29 0.01

5 5

1.69 0.32 0.011.73 0.290.33 0.0019.0 0.9 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

1.67 0.45 Consensus box encloses ±2×MADe around consensus medians.0.03 0.01 Plot encloses ±80 % around consensus medians.

Bsitosterol, mg/g

N

%RSD

NIST

±U 95

MADe

Median

Mean

Unknown: SRM 3250

B126

B119

B113 B111

B106

0.5 1 1.5 2 2.5 

0.5 0.4 0.3 0.2 0.1 NIST Consensus

Bsitosterol in Control (SRM 3251), mg/g

Bsitosterol in Unknown (SRM 3250), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3251 A1 B1 C1 Mean s total 

B106 0.57 0.1 0.09 0.09 0.09 0.00B111 0.25 0.04 0.04 0.05 0.04 0.00B113 0.3 0.09 0.09 0.08 0.08 0.01B119 0.27 0.05 0.04 0.04 0.04 0.01B126 0.34 0.04 0.04 0.04 0.04 0.00

5 5

0.35 0.06 0.000.30 0.040.07 0.0021.9 10.2 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

0.25 0.048 Consensus box encloses ±2×MADe around consensus medians.0.02 0.001 Plot encloses ±80 % around consensus medians.

Unknown: SRM 3250

±U 95

MADe

Median

Mean

Stigmasterol, mg/g

N

%RSD

NIST

B126

B119

B113

B111

0.1 0.2 0.3 0.4 

0.07 0.06 0.05 0.04 0.03 0.02 0.01

NISTConsensus

Stigmasterol in Control (SRM 3251), mg/

Stigmasterol in Unknown (SRM 3250), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3247 A1 B1 C1 Mean s total 

B103 47.7 8.29 8.3 8.27 8.29 0.02B105 43.19 7.45 7.42 7.42 7.43 0.02B106 48.6 8.67 8.77 8.66 8.70 0.06B110 45.35 7.04 7.18 6.96 7.06 0.11B111 40.3 7.2 6.97 7.05 7.07 0.12B112 1.56 8.36 8.46 8.45 8.42 0.05B113 37.7 8.05 7.76 8.03 7.95 0.16B118 48.49 8.14 8.3 8.39 8.28 0.13B119 45.9 7.37 7.4 7.08 7.28 0.18B121 45.3 7.91 8.04 7.84 7.93 0.10B123 20.6 20. 21.4 20.67 0.70B124 49. 8.34 8.74 8.61 8.56 0.20B126 45.6 8.3 7.9 7.7 7.97 0.31B127 46.2 8.1 8.1 8. 8.07 0.06

13 14

41.91 8.83 0.2345.60 8.02

3.57 0.71

7.8 8.8 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

45.10 7.56 Consensus box encloses ±2×MADe around consensus medians.

2.30 0.20 Plot encloses ±40 % around consensus medians.

Quercetin, mg/g

N

%RSD

NIST

±U 95

MADe

Median

Mean

Unknown: SRM 3248

B127 B126

B124

B123

B121

B119

B118

B113

B112

B111 B110

B106

B105

B103

28 36 44 52 

11 1098765

NISTConsensus

Quercetin in Control (SRM 3247), mg/g

Quercetin in Unknown (SRM 3248), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3247 A1 B1 C1 Mean s total 

B103 57.7 10. 10. 10.1 10.03 0.06B105 38.95 6.69 6.73 6.73 6.72 0.02B106 36.9 6.53 6.51 6.49 6.51 0.02B110 40.31 6.4 6.38 6.19 6.32 0.12B111 36.2 6.48 6.28 6.46 6.41 0.11B112 0.85 6.96 7.01 6.93 6.97 0.04B113 31.3 6.71 6.36 6.57 6.55 0.18B118 36.8 6.55 6.53 6.63 6.57 0.05B119 39.4 6.34 6.41 6.12 6.29 0.15B121 40.3 7.11 7.25 7.18 7.18 0.07B123 23.5 22.9 24. 23.47 0.55B124 39. 7.53 6.93 6.88 7.11 0.36B126 38.4 6.9 7. 6.7 6.87 0.15B127 40.9 7.2 7.2 7.1 7.17 0.06

13 14

36.69 8.15 0.2038.95 6.79

2.89 0.52

7.4 7.6 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

40.80 7.19 Consensus box encloses ±2×MADe around consensus medians.

1.50 0.35 Plot encloses ±35 % around consensus medians.

Unknown: SRM 3248

±U 95

MADe

Median

Mean

Kaempferol, mg/g

N

%RSD

NIST

B127

B126

B124

B123

B121

B119

B113 B118

B112

B111 B110

B106

B105

30 35 40 45 

98765

NISTConsensus

Kaempferol in Control (SRM 3247), mg

Kaempferol in Unknown (SRM 3248), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab SRM 3247 A1 B1 C1 Mean s total 

B103 10.6 1.95 1.97 1.98 1.97 0.02B105 9.83 1.65 1.71 1.7 1.69 0.03B106 10.2 1.83 1.9 1.91 1.88 0.04B110 10.68 1.7 1.69 1.64 1.68 0.03B111 10.4 1.89 1.86 1.88 1.88 0.02B112 0.02 0.16 0.14 0.15 0.15 0.01B113 9.08 2.04 1.97 2.01 2.01 0.04B118 11.96 1.74 1.74 1.81 1.77 0.04B119 10.5 1.6 1.72 1.6 1.64 0.07B123 3.7 3.6 3.8 3.70 0.10B124 9.01 1.63 1.57 1.58 1.59 0.03B126 10.2 1.8 1.8 1.8 1.80B127 9.6 1.7 1.7 1.7 1.70

12 13

9.34 1.80 0.04

10.20 1.77

0.65 0.17

6.4 9.6 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

10.80 1.90 Consensus box encloses ±2×MADe around consensus medians.

0.65 0.11 Plot encloses ±35 % around consensus medians.

Isorhamnetin, mg/g

N

%RSD

NIST

±U 95

MADe

Median

Mean

Unknown: SRM 3248

B127

B126

B124

B123

B119

B118

B113

B112

B111

B110

B106

B105

B103

7 8 9 10 11 12 

2.252 1.75 1.5 1.25

NISTConsensus

Isorhamnetin in Control (SRM 3247), mg

Isorhamnetin in Unknown (SRM 3248), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab not available A1 B1 C1 Mean s total 

B102 1.31 1.28 1.28 1.29 0.02B103 0.8 0.8 0.8 0.80 0.00B105 0.82 0.9 0.9 0.87 0.05B106 1.08 1.05 1.07 1.07 0.02B108 1.16 1.17 1.19 1.17 0.02B109 1.09 1.07 1.1 1.09 0.01B110 1.81 1.86 1.73 1.80 0.07B111 1.05 0.99 0.98 1.01 0.04B113 1.36 1.33 1.38 1.36 0.03B114 1.02 0.99 0.98 1.00 0.02B115 1.96 1.27 1.43 1.55 0.36B116 0.65 0.57 0.67 0.63 0.06B118 1.52 1.53 1.65 1.57 0.07B119 0.84 0.82 0.82 0.82 0.01B120 0.95 0.99 0.96 0.97 0.02B123 1.31 1.19 1.16 1.22 0.08B124 1.05 1.05 1.08 1.06 0.02B125 0.96 0.95 0.95 0.95 0.00B126 0.87 0.84 0.81 0.84 0.03B127 1. 1. 1.01 1.00 0.01B128 0.87 0.88 0.86 0.87 0.01

21

1.09 0.091.01

1.00 0.25

1.0 24.5 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

1.05 Consensus box encloses ±2×MADe around consensus medians.0.05 Plot encloses ±50 % around consensus medians.

Unknown: SRM 3280

±U 95

MADe

Median

Mean

VitaminB1, mg/g

N

%RSD

NIST

B124B123B120B119B118B116B115B114B113B111B110B109B108B106B105B103B102

15421098765

21

NISTConsensus

VitaminB1 in Control (not available), mg/

VitaminB1 in Unknown (SRM 3280), mg/g
Dietary Supplements Quality Assurance Program

 May 2008 Study - Round B

Control

Lab not available A1 B1 C1 Mean s total 

B102 1.3 1.32 1.31 1.31 0.01B103 1.3 1.3 1.4 1.33 0.06B105 1.3 1.28 1.29 1.29 0.01B106 1.64 1.62 1.65 1.64 0.02B108 1.27 1.27 1.29 1.28 0.01B109 1.18 1.14 1.15 1.16 0.02B110 1.52 1.64 1.58 1.58 0.06B111 1.5 1.57 1.38 1.48 0.10B113 1.13 1.11 1.19 1.14 0.04B114 0.85 0.96 0.92 0.91 0.06B115 2.47 2.05 1.94 2.15 0.28B116 1.2 1.3 1.2 1.23 0.06B118 1.14 1.16 1.16 1.15 0.01B119 1.09 1.19 1.19 1.16 0.06B120 1.01 1.02 1. 1.01 0.01B123 1.43 1.45 1.36 1.42 0.05B124 1.27 1.32 1.32 1.30 0.03B125 1.45 1.44 1.44 1.44 0.01B126 1.3 1.35 1.33 1.33 0.02B127 1.24 1.24 1.26 1.25 0.01B128 0.99 1.03 1.06 1.03 0.04

21

1.31 0.071.29

1.00 0.20

1.0 15.4 Precision bars span ±2×stotal about Lab mean values.

 NIST box encloses ±U 95 region around NIST values.

1.27 Consensus box encloses ±2×MADe around consensus medians.0.07 Plot encloses ±45 % around consensus medians.

VitaminB2, mg/g

N

%RSD

NIST

±U 95

MADe

Median

Mean

Unknown: SRM 3280

B128B119 B118B116B115B114B113B111B110B109B108B106B105B103B102

15431098765

21

NISTConsensus

VitaminB2 in Control (not available), mg/

VitaminB2 in Unknown (SRM 3280), mg/g