Standard reference materials for foods and dietary ... - CiteSeerX

Anal Bioanal Chem (2007) 389:171–178 DOI 10.1007/s00216-007-1315-y

INDUSTRY NEWS

Standard reference materials for foods and dietary supplements Katherine E. Sharpless & Jeanice Brown Thomas & Steven J. Christopher & Robert R. Greenberg & Lane C. Sander & Michele M. Schantz & Michael J. Welch & Stephen A. Wise

Received: 31 January 2007 / Revised: 2 April 2007 / Accepted: 20 April 2007 / Published online: 30 May 2007 # Springer-Verlag 2007

Abstract Well-characterized certified reference materials are needed by laboratories in the food testing, dietary supplement, and nutrition communities to facilitate compliance with labeling laws and improve the accuracy of information provided on product labels, so that consumers can make good choices. As a result of the enactment of the Nutrition Labeling and Education Act of 1990 and the Infant Formula Act of 1980, the National Institute of Standards and Technology (NIST) worked to develop a series of food-matrix standard reference materials (SRMs) characterized for nutrient concentrations. These include SRM 1544 Fatty Acids and Cholesterol in a Frozen Diet Composite, SRM 1546 Meat Homogenate, SRM 1548a Typical Diet, SRM 1566b Oyster Tissue, SRM 1846 Infant Formula, SRM 1946 Lake Superior Fish Tissue, SRM 1947 Lake Michigan Fish Tissue, SRM 2383 Baby Food Composite, SRM 2384 Baking Chocolate, SRM 2385 Slurried Spinach, and SRM 2387 Peanut Butter. With the enactment of the Dietary Supplement Health and Education Act of 1994, NIST has been working to develop suites of dietary supplement SRMs characterized for active and marker compounds and for toxic elements and pesticides, where appropriate. An updated SRM 1588b Organics in Cod Liver Oil, a suite of ephedra-containing materials (SRMs 3240–3245), a carrot extract in oil (SRM 3276), and a suite of ginkgo-containing materials (SRMs 3246–3248) are available. Several other materials are currently in K. E. Sharpless (*) : J. B. Thomas : S. J. Christopher : R. R. Greenberg : L. C. Sander : M. M. Schantz : M. J. Welch : S. A. Wise Analytical Chemistry Division, National Institute of Standards and Technology, 100 Bureau Drive Stop 8390, Gaithersburg, MD 20899-8390, USA e-mail: [email protected]

preparation. Dietary supplements are sometimes provided in forms that are food-like; for these, values may also be assigned for nutrients, for example SRM 3244 EphedraContaining Protein Powder. Both the food-matrix and dietary supplement reference materials are intended primarily for validation of analytical methods. They may also be used as “primary control materials” in assignment of values to in-house (secondary) control materials to confirm accuracy and to establish measurement traceability to NIST. Keywords Dietary supplement . Food . Reference material . Standard reference material

Introduction The Infant Formula Act of 1980 and the Nutrition Labeling and Education Act of 1990 (NLEA) [1, 2] were the original driving forces behind the National Institute of Standards and Technology’s (NIST’s) introduction of food-matrix standard reference materials (SRMs) with values assigned for nutrients. (A reference material is a “material or substance one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials” [3]. A certified reference material (CRM) is a “reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence” [3]. CRMs produced by NIST are known as SRMs.) NLEA requires that labels on processed foods distributed in the US specify the amount of total fat,

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saturated fat, cholesterol, total carbohydrate, dietary fiber, sugars, protein, vitamin A, vitamin C, sodium, calcium, and iron contained in a single serving. In addition to this, the Food and Drug Administration published a final rule that amended labeling regulations so that trans fatty acids also must be declared on the label, effective January 1, 2006 [4]. The manufacturer may voluntarily provide information about any other vitamin, mineral, or nutrient to assist the consumer in maintaining a healthy diet. The Infant Formula Act requires that nutrients contained in infant formula fall within a specified range or above a specified minimum. In response to these laws NIST began to produce food-matrix SRMs with values assigned for organic nutrients; before this approximately fifteen food-matrix materials were available (e.g., SRM 1549 Non-Fat Milk Powder, SRM 1567 Wheat Flour, SRM 1577 Bovine Liver) but they were characterized solely for element content. Several reference materials developed by Agriculture Canada and distributed by NIST were also available with values assigned for elements [5]; values for proximates (fat, protein, carbohydrate) in six of these materials were added after they were originally released [6]. With regard to materials containing trans fatty acids, SRMs 1846 Infant Formula and 1946 Lake Superior Fish Tissue have reference values of 4.00± 0.54% and 0.0098±0.0010% for (E)-9-octadecenoic acid (elaidic acid) as the triglyceride. The certified value of 4% in SRM 1846 is equivalent to 0.64 g in 16 g material, the approximate amount that would be used to prepare a 100 mL (4 oz) bottle for a baby if this material were intended for that purpose. (Note that a trans fatty acid concentration greater than 0.5 g per serving requires that a non-zero value be provided on the nutrition label; concentrations below 0.5 g per serving can be shown as 0 g [4]). Two additional laws that affect the food community were passed more recently. The Dietary Supplement Health and Education Act of 1994 (DSHEA) defines dietary supplements and regulates them as foods; it requires that products bear a supplements facts panel similar to the nutrition facts panel required by NLEA for food labeling [7]. In addition, DSHEA states that the US Food and Drug Administration (FDA) will issue good manufacturing practices (GMPs) for the dietary-supplement industry [7]. Manufacturers will be required to evaluate the identity, purity, quality, strength, and composition of their dietary supplements’ ingredients and finished products, in part, by use of SRMs as laboratory controls [8]. Accurate label information will enable publichealth agencies to draw conclusions about the use of individual dietary supplements and enable consumers to make sound choices. Accurate measurements of contaminated or adulterated ingredients and products from the marketplace will also, ultimately, improve public health and safety. The Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) requires that the labels on products

Anal Bioanal Chem (2007) 389:171–178

containing major allergenic foods as ingredients declare their presence; this applies to products that were labeled after January 1, 2006 [9]. Major allergenic foods in the US include peanuts, egg, milk, wheat, soy, finfish, crustacean shellfish, and tree nuts. Reference materials are important to demonstrate that the test kits typically used for allergen determinations are, in fact, detecting allergens as they should be. “Pure” allergenic foods, for example whole milk powder or whole egg powder, have been available for seven of the eight allergens (all but tree nuts) from NIST, the National Research Council Canada, and the Institute for Reference Materials and Measurements (IRMM) in the European Union (EU). Until IRMM’s recent release of peanut materials, however, no reference materials were available that had been developed specifically for the purpose of allergen testing. Although some food SRMs have been used to evaluate allergen test kits, no allergen information is provided on their certificates of analysis. To facilitate compliance with these laws, well-characterized certified reference materials (CRMs) are needed by laboratories generating information for labels and for the food testing and nutrition communities in general. Such CRMs also provide measurement traceability for food exports to facilitate acceptance in foreign markets, assess compliance with legal limits, and improve the accuracy of label information that is provided to assist consumers in making sound choices. NIST food-matrix reference materials can be used for method validation—if the results for the new method agree with the reference material’s assigned values the method will likely give correct values for other similar samples—and for quality assurance in the analysis of routine or in-house (secondary) control samples.

Value assignment and selection of materials NIST has three categories of assigned values—certified, reference, and information. A certified value is a value for which NIST has the highest confidence in its accuracy in that all known or suspected sources of bias have been investigated or accounted for [10]. A reference value is a value that is the best estimate of the true value based on available data; the value does not meet the NIST criteria for certification, however, and is provided with associated uncertainties that may reflect only measurement reproducibility, may not include all sources of uncertainty, or may reflect a lack of sufficient statistical agreement among multiple analytical methods [10]. Although an information value is regarded as of interest to the SRM user, either insufficient information is available to assess the uncertainty or the uncertainty is relatively large [10]. Information values are usually reported with no associated uncertainty. Certified values are typically assigned on the basis of a


combination of results from two or more independent NIST methods; the idea here is that biases inherent to one will not be present in the other if the methods are truly independent. Thus, if the results from the two methods agree, they are likely providing the “true” value. Certified values can also be assigned by combining NIST data with data provided by collaborating laboratories. If an assigned value is based solely on data provided by a collaborating laboratory it will either be a reference or information value; certified values cannot be assigned based solely on data provided by collaborating laboratories. Reference values can also be assigned when NIST data are included—if the expanded uncertainty is larger than expected or if there is some question about the identity of the analyte (e.g., perhaps isomerization occurred during sample preparation for determination of trans-β-carotene, therefore reference values might be assigned for the cis and trans isomers and a certified value for total β-carotene). Because of the resources required for assigning values for the large number of measurands (proximates, vitamins, elements, fatty acids, amino acids, etc.) that may be of interest in food-matrix reference materials, NIST has relied on the assistance of collaborating laboratories (largely the Food Products Association’s Food Industry Analytical Chemists Committee for food-matrix materials) for value assignment for these materials. To visualize the need for reference materials for foods of varying composition, NIST has used a triangle developed by AOAC International, an organization that conducts collaborative studies to evaluate analytical methods. To demonstrate that a method is applicable to a variety of foods, AOAC International’s Task Force on Methods for Nutrition Labeling developed a triangle in which foods could be positioned on the basis of their fat, protein, and carbohydrate content [11, 12]. AOAC’s belief is that one or two foods within a sector are representative of other foods within that sector, and if an analytical method provides accurate results for the test foods it should also provide accurate results for other foods in the same sector. Similarly, reference materials in a particular sector should also be representative of other foods in that sector [12]. To that end, we began to “fill the triangle” with reference materials; NIST food-matrix SRMs and RMs that are currently available are shown in the triangle in Fig. 1, occupying all nine sectors or, occasionally, the lines between the sectors. The user should bear in mind, however, that a match of analyte concentration may be as important as a match of the fat/protein/ carbohydrate composition. For example, in an analysis for a low concentration of sodium, it may be more important to match the control and test samples’ sodium concentrations than it would be to match the fat or protein content. To facilitate such matching, the assigned values for NIST’s food-matrix reference materials, along with materials avail-

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able from other producers, were recently summarized in supplementary material associated with Ref. [13], and this information will not be repeated here. (Note, however, that users are advised to consult certificates of analysis (e.g., http://www.nist.gov/srm and http://www.irmm.jrc.be/html/ reference_materials_catalogue/index.htm) to ensure that values have not been changed since the publication of that summary). NIST’s food-matrix materials and their release and certificate revision dates are listed in Table 1. Certificates of analysis (or, for the RMs, reports of investigation) may be revised to add certified or reference values if additional values are assigned during the lifetime of the material. (Certificates may also be updated for other reasons, including, for example, revision if an assigned value is no longer valid, extension of the expiration date if appropriate, or to make an editorial change.) A material for which most of these types of revisions have occurred is SRM 1846 Infant Formula. This SRM was released in May 1996 with certified values for vitamins A, E, C, B2, B6, and niacin based on a combination of NIST data from a single method and collaborating laboratories’ data. These laboratories also measured proximates, elements, and vitamins, and reference values were assigned in cases where NIST had not also made measurements. In June 1998, iodine was changed from a reference value to a certified value when data from two collaborating laboratories became available and were combined with the original NIST data. In October 1999, reference values for individual fatty acids were assigned using data from four collaborating laboratories. In 1999, vitamin K was changed from an information value to a reference value based on data from an AOAC collaborative study (34 laboratories) for vitamin K. The stability of the material was monitored and the expiration 100% Fat 0% Protein 0% Carbohydrate

+ SRM 1563

1 SRM 2384 +

SRM 2387

2 +

+

3

SRM 1546 RM 8415

++

4

+ RM 8435 SRM 1548a SRM 1544 + + 6 7 8 5 SRM 2383 + RM 8432 RM 8433 SRM 1566b + + RM 8436 + SRM 1570a 0% Fat + + SRM 2385 0% Protein 100% Carbohydrate

+ SRM 1946

SRM 1846

SRM 1947

9 +

RM 8418

SRM 3244

+

0% Fat 100% Protein 0% Carbohydrate

Fig. 1 Location of food-matrix reference materials available from NIST in the AOAC fat–protein–carbohydrate triangle

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Table 1 Number, name, original date of issue, and revision dates for NIST’s food and dietary supplement SRMs with values assigned for proximates, vitamins, elements, etc SRM 1544 1546

Name Fatty Acids and Cholesterol in a Frozen Diet Composite Meat Homogenate

Original date of issue February 15, 1996 May 10, 1999

1548a

Typical Diet

February 2, 1998

1563

Cholesterol and Fat-Soluble Vitamins in Coconut Oil (Natural and Fortified)

July 21, 1987

1566b 1570a

Oyster Tissue Trace Elements in Spinach Leaves

January 17, 2001 October 20, 1994

1588ba 1845

Organics in Cod Liver Oil Cholesterol in Egg Powder

February 7, 2006 January 9, 1989

1846

Infant Formula

May 8, 1996

1946

Lake Superior Fish Tissue

February 20, 2003

1947 2383 2384

Lake Michigan Fish Tissue Baby Food Composite Baking Chocolate

Expected 2007 December 23, 1997 March 22, 2002

2385 2387

Slurried Spinach Peanut Butter

December 9, 2003 March 14, 2003

3240 3241 3242 3243 3244 3245 3246 3247 3248 3249 3276

Ephedra sinica Stapf Ephedra sinica Stapf Native Extract Ephedra sinica Stapf Commercial Extract Ephedra-Containing Solid Oral Dosage Form Ephedra-Containing Protein Powder Ephedra Dietary Supplement Suite Ginkgo biloba (Leaves) Ginkgo biloba Extract Ginkgo-Containing Tablets Ginkgo Dietary Supplement Suite Carrot Extract in Oil

March 20, 2006 June 19, 2006 June 19, 2006 March 20, 2006 March 20, 2006 June 19, 2006 Expected 2007 Expected 2007 Expected 2007 Expected 2007 Expected 2007

Name

Original Date of Issue

Updates

8415

Whole Egg Powder

September 24, 1993

8418

Wheat Gluten

September 24, 1993

8432 8433 8435 8436

Corn Starch Corn Bran Whole Milk Powder Durum Wheat Flour

September September September September

June 14, 2005 April 28, 1999 October 4, 1999 February 18, 1994 October 4, 1999 October 4, 1999 April 29, 1999 October 4, 1999

RM

24, 24, 24, 24,

1993 1993 1993 1993

Revision dates February 9, 2004 January 6, 2004 October 26, 2004 April 2, 2003 June 1, 2000 February 28, 2003 May 5, 1999 November 7, 1996 December 8, 1995 August 31, 2001 July 15, 1996 Expected 2007 February 11, 2003 April 25, 1994 March 22, 2006 January 24, 2006 August 25, 2004 January 14, 2004 October 17, 2003 September 25, 2001 October 4, 1999 June 2, 1998 June 9, 2004 September 29, 2003 July 26, 2002 January 8, 2007 September 28, 2004 June 4, 2003 January 8, 2007 September 29, 2004

Reasons for updates are provided on each material’s certificate of analysis in a “revision history” section (http://www.nist.gov/srm). Revisions may result when assigned values are added or removed, when expiration dates are extended, or when an editorial change is necessary. a SRM 1588b is the same material as SRM 1588, which was originally characterized in 1989. Values were added in 1998, when the material became SRM 1588a, and again in 2006 when it became SRM 1588b


date was extended several times. In 2001 the value for vitamin A was changed from certified to reference because of increasing difficulty in extracting vitamin A from the material. In 2004, the reference value for vitamin A and the certified value for vitamin E were removed from the certificate. The extraction difficulties are believed to result from hardening of the encapsulation surrounding the fat-soluble vitamins that were added to the material; concentrations of unencapsulated tocopherols (i.e., δ- and γ-tocopherol) have remained unchanged. When last assessed (2006) the certified values for three water-soluble vitamins were still valid. Because of the age of this material, however, and the current absence of certified values for vitamins A and E, a replacement material is now being prepared. SRM 1849 Infant/Adult Nutritional Formula is a hybrid of infant and adult formulas and is expected to have certified values for a broader range of analytes (vitamins, fatty acids, elements) than did its predecessor. Reference values for proximates, nucleotides, and amino acids are also expected. Further to the discussion of stability assessment, expiration dates are typically assigned on the basis of past experience with similar materials and analytes. To enhance long-term stability a variety of factors (inclusion of stabilizers, packaging, storage conditions, etc.) are optimized before value assignment. Stability of currently available materials is monitored over time—as part of scheduled stability assessment or when the material is analyzed as a control during value assignment of a similar material-and long-term stability studies are conducted on series of related materials (e.g., SRM 968, 968a, 968b, and 968c Fat-Soluble Vitamins, Carotenoids, and Cholesterol in Human Serum). When instability is identified, certificates are revised as appropriate, e.g., removal of a value that is no longer valid (as described above), assignment of a new value, etc.-and customers are notified. Concentrations for active and/or marker compounds are being assigned to several dietary supplement materials (Table 2). SRMs for botanical materials are provided in suites that present different analytical challenges, i.e., plant, extract, and “finished products.” Because of safety concerns, initial efforts focused on ephedra. Ephedra-containing products for weight loss and body-building were available in the US before 2004, at which time the FDA declared them adulterated. Five materials and an SRM consisting of two bottles of each of the five materials were produced; values are assigned for ephedrine alkaloids in these materials, as shown in Table 2 [14]. Values are assigned for caffeine in SRMs 3243 and 3244, and nutrients in SRM 3244. The second priority, identified on the basis of its market share in the US, was ginkgo. Some reports indicate that ginkgo improves cognitive function, among other things [15]. A suite three materials and a combination were prepared: SRM 3246 Ginkgo biloba (Leaves), SRM

175

3247 Ginkgo biloba Extract, SRM 3248 Ginkgo-Containing Tablets, and SRM 3249 Ginkgo Dietary Supplement Suite [16]. Values are assigned for flavonoid aglycones, ginkgolides, and bilobalide in these materials, as shown in Table 2. Two single materials—SRM 1588b Organics in Cod Liver Oil [17] and SRM 3276 Carrot Extract in Oil [18]—have also been prepared. SRM 1588b is a result of recharacterization of SRM 1588a, with values now assigned for individual fatty acids, including omega-3 fatty acids, and polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and chlorinated pesticides. SRM 3276 has values assigned for carotenoids, tocopherols, and fatty acids. Foods can also contain non-nutrient compounds with positive health implications, for example catechins, and compounds with negative health implications, for example toxic elements and potential carcinogens. In addition to the active and marker compounds in dietary supplements mentioned above, several food and dietary supplement reference materials are available with values assigned for non-nutrient compounds (Tables 3 and 4). Because of the large number of compounds, values for individual amino acids, PCBs, PBDEs, and pesticides are not shown in the tables, but the number of certified or reference values assigned for these compounds is provided. Four of the materials, SRM 1566b Oyster Tissue, SRM 1588b Organics in Cod Liver Oil, SRM 1946 Lake Superior Fish Tissue, and SRM 1947 Lake Michigan Fish Tissue, were developed primarily for the determination of inorganic and organic environmental contaminants. Because these materials are also foods (or supplements, in the case of cod liver oil), however, they can serve as both environmental and food/ supplement SRMs.

Identification of priorities and in-progress and future activities To assess the needs of a user community and to make optimum use of the resources available to NIST, NIST has used input from users of reference materials to help generate and prioritize a list of analytes and matrices with potential for development into SRMs. SRM 1546 Meat Homogenate was developed at the request of the US Department of Agriculture’s (USDA’s) Food Safety Inspection Service. SRM 2384 Baking Chocolate and SRM 2385 Slurried Spinach were developed as a result of a NISTsponsored workshop in 1997 that was held to identify SRM needs of the food industry. Materials in sectors 2 and 7 of the AOAC triangle (Fig. 1) were designated as high priorities as a result of that workshop. SRM 2387 Peanut Butter was produced to populate sector 3 and because an SRM with values assigned for aflatoxins and individual

176


Table 2 Mass fractions, in the units shown, of active/marker compounds in SRMs 3240 Ephedra sinica Stapf, 3241 Ephedra sinica Stapf Native Extract, 3242 Ephedra sinica Stapf Commercial Extract, 3243 Ephedra-Containing Solid Oral Dosage Form, 3244 Ephedra-

Containing Protein Powder, 3246 Ginkgo biloba (Leaves), 3247 Ginkgo biloba Extract, 3248 Ginkgo-Containing Tablets, 1588b Organics in Cod Liver Oil, and 3276 Carrot Extract in Oil

Mass fractions of active marker compounds

Ephedrine alkaloids in ephedra SRMsa (mass fraction in mg g−1) Ephedrine Methylephedrine Pseudoephedrine Methylpseudoephedrine Norephedrine Norpseudoephedrine Total Alkaloids

SRM 3240

SRM 3241

SRM 3242

SRM 3243

SRM 3244

11.31±0.76 1.18±0.14 3.53±0.26 0.046±0.015 0.44±0.09 0.65±0.14 17.0±1.2

28.86±1.17 2.61±0.51 10.74±1.11 0.11±0.09 0.48±0.20 0.44±0.17 43.3±2.7

78.1±2.3 2.77±0.57 9.27±0.94 0.124±0.044 0.57±0.18 0.40±0.16 91.2±2.0

11.21±0.42 0.323±0.031 2.81±0.11 0.020±0.011 0.160±0.026 0.186±0.029 14.78±0.54

0.242±0.038 0.0075±0.0024 0.0361±0.0086 0.0030 0.0034 0.0003 0.296±0.067

SRM 3246

SRM 3247

SRM 3248

2.69±0.31 3.02±0.41 0.517±0.099 6.22±0.77 0.57±0.28 0.470±0.090 0.59±0.22 0.18±0.10 1.52±0.40 3.3±1.1

45.1±4.6 40.8±3.0 10.8±1.3 96.8±8.3 11.6±1.7 5.92±0.45 12.4±1.4 3.9±1.5 28.5±2.1 62.4±5.7

7.56±0.40 7.19±0.70 1.90±0.22 16.6±1.2 2.42±0.63 1.12±0.20 2.36±0.42 0.81±0.36 5.7±1.2 11.8±1.4

Flavonoid aglycones and terpene lactones in ginkgo SRMsa (mass fraction in mg g−1)

Quercetin Kaempferol Isorhamnetin Total aglycones Ginkgolide A Ginkgolide B Ginkgolide C Ginkgolide J Bilobalide Total terpene lactones

Fatty acids (as triglycerides) in cod liver oil and carrot extract in oil (mass fraction in %) SRM 3276 Tetradecanoic acid (C14:0) (myristic acid) Pentadecanoic acid (C15:0) Hexadecanoic acid (C16:0) (palmitic acid) (Z)-9-Hexadecenoic acid (C16:1 n-7) (palmitoleic acid) Heptadecanoic Acid (C17:0) Octadecanoic acid (C18:0) (stearic acid) (Z)-9-Octadecenoic acid (C18:1 n-9) (oleic acid) (Z)-11-Octadecenoic acid (C18:1 n-7) (vaccenic acid) (Z,Z)-9,12-Octadecadienoic acid (C18:2 n-6) (linoleic acid) (Z,Z,Z)-9,12,15-Octadecatrienoic acid (C18:3 n-3) (linolenic acid) (Z,Z,Z)-6,9,12-Octadecatrienoic acid (C18:3 n-3) (γ-linolenic acid) Eicosanoic acid (C20:0) (arachidic acid) (Z)-11-Eicosenoic acid (C20:1 n-9) (gondoic acid) Eicosatrienoic acid (C20:3) Eicosapentaenoic acid (C20:5) Docosanoic acid (C22:0) (behenic acid) Docosapentaenoic acid (C22:5) Docosahexaenoic acid (C22:6) Tetracosanoic acid (C24:0) (lignoceric acid) (Z)-Tetracosenoic acid (C24:1 n-9) (nervonic acid) Carotenoids and Tocopherols in SRM 3276 (mass fraction in mg g−1) trans-β-carotene 9-cis-β-carotene total cis-β-carotene total β-carotene trans-α-carotene δ-tocopherol γ-tocopherol

3.35±0.27 0.288±0.021 8.51±0.97 6.80±0.91 1.82±0.20 13.3±1.7 4.34±0.60 2.00±0.27

SRM 1588b

1.36±0.05 0.0147±0.0014 0.0213±0.0017 1.14±0.02 3.68±0.06 0.519±0.012 6.64±0.11 0.816±0.014

0.138±0.019 9.5±1.7 0.137±0.020 9.04±0.82

0.0578±0.0025 0.353±0.006

0.126±0.016 1.21±0.14 13.6±1.5 0.0242±0.0018 0.379±0.047 30.7±2.2 11.4±1.6 22.0±2.4 50.8±3.6 3.11±0.56 372±34 443±42

Certified values are shown in bold, reference values in normal type; information values have no associated uncertainties. All values are provided on an as-received basis except where noted. Information related to analytical methods, calculation of uncertainties, etc. are provided in the Certificates of Analysis for individual materials (available at http://www.nist.gov/srm) a Results provided on a dry-mass basis


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Table 3 Assigned values for toxic elements (arsenic, cadmium, lead, and mercury) and methylmercury in food and dietary supplement SRMs SRM

As

Cd

Pb

1548a 1566b 1570a 1946 1947 3240 3241 3242 3243 3244 3246 3247 3248

0.20±0.01 7.65±0.65 0.068±0.012 0.277±0.010 0.732±0.03 0.265±0.016 1.285±0.081 1.030±0.033 0.554±0.018 0.0196±0.0027

0.035±0.0015 2.48±0.08 2.89±0.07

0.044±0.009 0.308±0.009

0.0906±0.0039 0.0587±0.0036 0.0538±0.0032 0.1218±0.0033 0.01266±0.00026 0.0208±0.0011 0.0075±0.0008 0.00156±0.00019

0.314±0.012 0.0565±0.0043

0.241±0.012 0.362±0.014 0.692±0.056 0.0270±0.0027 0.995±0.030 4.273±0.031 0.7753±0.0089

Hg

Methylmercury

0.0371±0.0013 0.030±0.003 0.433±0.009 0.2535±0.0053 0.0167±0.0005 0.00383±0.00029 0.00418±0.00042 0.00900±0.00044 0.000253±0.000033 0.02308±0.00017

0.0132±0.0007 0.394±0.015 0.233±0.010

0.000271±0.000034

Certified values are provided in bold, and reference values are provided in normal typeface. All values are provided on an as-received basis except where noted. All values are expressed as mass fractions in units of mg kg−1 . Uncertainties are expanded uncertainties, calculated as described in the certificate of analysis for each material. Information related to analytical methods, calculation of uncertainties, etc. is provided in the certificates of analysis for individual materials (available at http://www.nist.gov/srm)

amino acids had been requested. With the current availability of materials in (or on the borders of) all nine sectors of the AOAC triangle, efforts have shifted from the deliberate development of materials directed at the NLEA and the triangle to inclusion of nutrition information for materials being developed for other purposes. Similar to any commercial establishment, NIST monitors sales of SRMs; sales statistics will determine whether additional materials should be added to the triangle and whether materials should be replaced as they reach the end of their shelf lives. Two food-matrix materials are currently being developed. SRM 1849 Infant Adult Nutritional Formula, mentioned above, will replace SRM 1846 Infant Formula; more than 190 units of SRM 1846 were sold in 2006. In addition,

development of a fortified cereal SRM has begun. This material was requested by the USDA, two universities, and a multinational corporation (independently of each other); values are expected for proximates, vitamins, elements, and fiber. Production of SRMs for dietary supplements is continuing. Suites of SRMs for the following botanicals are being developed: saw palmetto, green tea, bitter orange, blueberries, cranberries, bilberries, black cohosh, soy, kudzu, and red clover. Where appropriate (e.g., soy, blueberries, cranberries), nutrient values will also be assigned for these materials. In addition, various omega-3 and omega-6 fatty acid-containing oils of botanical origin (e.g., perilla, evening primrose, flaxseed, borage) and a vegetable oil will be characterized for individual fatty acids and

Table 4 Assigned values for miscellaneous analytes in NIST’s food-matrix SRMs SRM Caffeine (mg kg−1) Synephrine (mg kg−1) Theobromine (mg kg−1) Total aflatoxins (ng g−1) (+)-Catechin (mg kg−1) (−)-Epicatechin (mg kg−1) Acrylamide (ng g−1) No. of amino acids No. of PCBs No. of PBDEs No. of pesticides

1588b

1946

1947

2384

2387

1060±50

3243a

3244a

76.5±4.1 0.54±0.19

2.99±0.54

11600±1100 5.0 ± 0.5 245±51 1220±240 138±17 27, 47 6 15, 3

30, 12 7, 3 15, 2

87.0±7.8 18

18

32, 13 7, 2 15, 2

Certified values are provided in bold, and reference values are provided in normal typeface. All values are provided on an as-received basis except where noted. All values are expressed as mass fractions in the units specified. Uncertainties are expanded uncertainties, calculated as described in the certificate of analysis for each material. The number of certified values for individual amino acids, polychlorinated biphenyl congeners (PCBs), and pesticides are provided in bold; the number of reference values are provided in normal typeface. The reader is advised to see the certificate of analysis for actual values. (Certificates are available at http://www.nist.gov/srm.) a Value is provided on a dry-mass basis

178

tocopherols/tocotrienols, respectively. A multivitamin/multielement tablet SRM is also nearing completion; this material will have values assigned for seventeen elements and fifteen vitamins and carotenoids. Isotope-dilution liquid chromatography–mass spectrometry (ID LC–MS) methods developed as part of certification efforts for this material will be used to assign vitamin concentrations in existing SRMs, as appropriate. The material RM 8445 Spray-Dried Whole Egg for Allergen Detection was produced by the FDA, Food Products Association (FPA), Health Canada, IRMM, and the Food Allergy Research and Resource Program (FARRP), University of Nebraska, for evaluation of test kits used for detecting the presence of egg. Some of this material was packaged by FDA for distribution by NIST, and the same material is expected to be distributed by the EU’s Institute for Reference Materials and Measurements. NIST expects to distribute other allergen-testing materials that are produced by these collaborating organizations. Acknowledgments Our sincere thanks go to the NIST analysts and statisticians and analysts at the collaborating laboratories who have assisted in the value-assignment of these reference materials. Partial funding for this work has been provided through NIH agreements Y1OD-1382 and Y2-OD-2331 with the Office of Dietary Supplements and through FDA agreement FDA-224-02-2751. Disclaimer Certain commercial products are identified to specify adequately the experimental procedure. Such identification does not imply endorsement or recommendation by the National Institute of Standards and Technology, nor does it imply that the materials identified are necessarily the best available for the purpose.

References 1. Infant Formula Act. Public Law 96–359 [H.R. 6940]; Sept 26, 1980 2. Nutrition Labeling and Education Act. Public Law 101–535 [H.R. 3562]; Nov 8, 1990 3. International vocabulary of basic and general terms in metrology, 2nd ed., BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML, International Organization for Standardization (ISO), 1993 (VIM)

Anal Bioanal Chem (2007) 389:171–178 4. Federal Register-68 FR 41433 July 11, 2003: Food Labeling: Trans Fatty Acids in Nutrition Labeling, Nutrient Content Claims, and Health Claims, http://www.cfsan.fda.gov/~lrd/fr03711a.html 5. Ihnat M (1994) J AOAC Int 77:1605–1627 6. Sharpless KE, Colbert JC, Greenberg RR, Schantz MM, Welch MJ (2001) Fresenius J Anal Chem 370:275–278 7. Dietary Supplement Health and Education Act. Public Law 103– 417 [S. 784]; Oct 25, 1994 8. “Current good manufacturing practice in manufacturing, packing, or holding dietary ingredients and dietary supplements,” (Federal Register Vol. 68, No. 49, Thursday, March 13, 2003, Docket No. 96N–0417; Section 111.60) http://www.fda.gov/ OHRMS/DOCKETS/98fr/03–5401.pdf 9. Food Allergen Labeling and Consumer Protection Act. Public Law 108–282, Title II [S. 741]; Aug 2, 2004 10. May W, Parris R, Beck C, Fassett J, Greenberg R, Guenther F, Kramer G, Wise S, Gills T, Colbert J, Gettings R, MacDonald B (2000) National Institute of Standards and Technology (NIST) Special Publication 260–136, US Government Printing Office, Washington DC http://www.cstl.nist.gov/ nist839/NIST_special_publications.htm 11. Wolf WR (1993) In: Sullivan DM, Carpenter DE (eds) Methods of analysis for nutrition labeling. AOAC International, Arlington, VA, pp 111–122 12. Wolf WR, Andrews KW (1995) Fresenius J Anal Chem 352:73–76 13. Phillips KM, Wolf WR, Patterson KY, Sharpless KE, Amanna KR, Holden JM (2007) Accred Qual Assur, in press 14. Sharpless KE, Anderson DL, Betz JM, Butler TA, Capar SG, Cheng J, Fraser C, Gay M, Gardner G, Howell D, Ihara T, Lam J, Long S, McCooeye M, Mackey EA, Mindak W, Mitvalsky S, Murphy KE, Phinney KW, NguyenPho A, Porter BJ, Roman M, Sander LC, Satterfield M, Scriver C, Sturgeon RE, Brown Thomas J, Vocke R, Wise SA, Wood LJ, Yang L, Yen JH, Ziobro G (2006) J AOAC Int 89:1483–1495 15. http://www.nlm.nih.gov/medlineplus/druginfo/natural/ patient-ginkgo.html, http://nccam.nih.gov/health/ginkgo/ (Accessed Jan 16, 2007) 16. Rimmer CA, Howerton SB, Sharpless KE, Sander LC, Long SE, Murphy KE, Porter BJ, Putzbach K, Rearick MS, Wise SA, Wood LJ, Zeisler R, Hancock DK, Yen JH, Betz JM, NguyenPho A, Yang L, Scriver C, Willie S, Sturgeon R, Schaneberg B, Nelson C, Skamarack J, Pan M, Levanseler K, Gray D, Waysek EH (2007) Anal Bioanal Chem, submitted for this issue 17. Certificate of Analysis, SRM 1588b Organics in Cod Liver Oil, National Institute of Standards and Technology, Gaithersburg, MD 18. Sharpless KE, Brown TJ, Duewer DL, Putzbach K, Rimmer CA, Sander LC, Schantz MM, Wise SA, Yarita T, Yen JH, (2007) Anal Bioanal Chem, this issue