Characterization (certification) of three wheat flours and a wheat gluten reference material (NIST RM 8436, 8437, 8438 and 8418) for essential and toxic major, minor and trace element constituents

Summary Three wheat flours, Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437), Soft Winter Wheat Flour (NIST RM 8438) and Wheat Gluten (NIST RM 8418) Reference Materials were characterized for essential and toxic major, minor and trace elemental composition by analysts in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods yielded 16–27 best estimate and 3–8 informational concentration values for each of these materials. These reference materials are intended for analytical quality control of element determinations in flour and flour products as well as other agricultural/food materials with related matrices.Contribution No. 92–145 from Centre for Land and Biological Resources Research     

Characterization (certification) of Bovine Muscle Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415) and Whole Milk powder (NIST RM 8435) Reference Materials for essential and toxic major, minor and trace element constituents

Summary Bovine Muscle Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415) and Whole Milk Powder (NIST RM 8435) Reference Materials were characterized for essential and toxic major, minor and trace element composition in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods yielded best estimate concentration values for 27, 23 and 21 elements, and informational concentration values for 5, 4 and 9 elements, respectively, in RM's 8414, 8415 and 8435. These Reference Materials are intended for analytical quality control of element determinations on meat, egg and milk-based products as well as agricultural/food materials with related matrices.Contribution no. 92–147 from Centre for Land and Biological Resources Research     

Summary of an interlaboratory characterization (certification) campaign to establish the elemental composition of a new series of agricultural/food reference materials

Summary Ten new Agricultural/Food Reference Materials (RMs) were characterized with respect to their elemental compositions via an interlaboratory characterization (certification) campaign. Chemical analyses were conducted in 73 cooperating laboratories applying 13 major classes of independently different analytical methods. A total of 213 best estimate values, and 65 informational values were obtained for Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Ti, V, W and Zn in the following RMs: Bovine Muscle Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415), Microcrystalline Cellulose (NIST RM 8416), Wheat Gluten (NIST RM 8418), Corn Starch (NIST RM 8432), Corn Bran (NIST RM 8433), Whole Milk Powder (NIST RM 8435), Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437) and Soft Winter Wheat Flour (NIST RM 8438).     

Biological Reference Materials for Quality Control of Elemental Composition Analytical Data

Twelve biological-matrix, agricultural/food reference materials, Corn Stalk (Zea Mays) (NIST RM 8412), Corn Kernel (Zea Mays) (NIST RM 8413), Bovine Musele Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415), Microcrystalline Cellulose (NIST RM 8416), Wheat Gluten (NIST RM 8418), Corn Starch (NIST RM 8432), Corn Bran (NIST RM 8433), Whole Milk Powder (NIST RM 8435), Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437) and Soft Winter Wheat Flour (NIST RM 8438) were developed. They were characterized with respect to elemental composition via two extensive international interlaboratory characterization campaigns providing 303 reference and informational concentration values for 34 elements (Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Ti, V, W, Zn) of nutritional, toxicological, and environmental significance. These products are available to the analytical community, for quality control of elemental composition analytical data, from the Standard Reference Materials Program, National Institute of Standards and Technology, Gaithersburg, MD, USA.     

Value assignment of nutrient concentrations in five standard reference materials and six reference materials

A number of food-matrix reference materials (RMs) are available from the National Institute of Standards and Technology (NIST) and from Agriculture Canada through NIST. Most of these materials were originally value-assigned for their elemental composition (major, minor, and trace elements), but no additional nutritional information was provided. Two of the materials were certified for selected organic constituents. Ten of these materials (Standard Reference Material [SRM] 1,563 Cholesterol and Fat-Soluble Vitamins in Coconut Oil [Natural and Fortified], SRM 1,566b Oyster Tissue, SRM 1,570a Spinach Leaves, SRM 1,974a Organics in Mussel Tissue (Mytilus edulis), RM 8,415 Whole Egg Powder, RM 8,418 Wheat Gluten, RM 8,432 Corn Starch, RM 8,433 Corn Bran, RM 8,435 Whole Milk Powder, and RM 8,436 Durum Wheat Flour) were recently distributed by NIST to 4 laboratories with expertise in food analysis for the measurement of proximates (solids, fat, protein, etc.), calories, and total dietary fiber, as appropriate. SRM 1846 Infant Formula was distributed as a quality control sample for the proximates and for analysis for individual fatty acids. Two of the materials (Whole Egg Powder and Whole Milk Powder) were distributed in an earlier interlaboratory comparison exercise in which they were analyzed for several vitamins. Value assignment of analyte concentrations in these 11 SRMs and RMs, based on analyses by the collaborating laboratories, is described in this paper. These materials are intended primarily for validation of analytical methods for the measurement of nutrients in foods of similar composition (based on AOAC INTERNATIONAL's fat-protein-carbohydrate triangle). They may also be used as "primary control materials" in the value assignment of in-house control materials of similar composition. The addition of proximate information for 10 existing reference materials means that RMs are now available from NIST with assigned values for proximates in 6 of the 9 sectors of the AOAC triangle. Five of these materials have values assigned for total dietary fiber-the first such information provided for materials available from NIST.     

Determination of copper, molybdenum and selenium in biological reference materials by inductively coupled plasma mass spectrometry

Summary In a contribution to the elemental characterization of 10 new reference materials, Bovine Muscle Powder (136), Corn Starch (162), Hard Red Spring Wheat Flour (165), Soft Winter Wheat Flour (166), Whole Milk Powder (183), Wheat Gluten (184), Corn Bran (186), Durum Wheat Flour (187), Whole Egg Powder (188) and Microcrystalline Cellulose (189), the total concentrations of Cu, Mo and Se were determined by the application of an analytical method based on isotope dilution inductively coupled plasma mass spectrometry. Cu and Mo contents were quantified by measurement of ⁶⁵Cu/⁶³Cu and ⁹⁷Mo/¹⁰⁰Mo isotopic ratios following spiking with ⁶⁵Cu and ⁹⁷Mo and digestion with nitric acid. Selenium was separated as hydrogen selenide from the matrix using sodium borohydride after spiking with ⁸²Se and acid digestion-dry ashing and quantified by measurement of the ⁸²Se/⁷⁸Se isotopic ratio. Comparison of these results with those from a variety of other methods and assessment of the procedures using certified reference materials indicated that the determinations of Cu, Mo and Se were performed without analytical bias.     

Recent developments in NIST botanical SRMs

The National Institute of Standards and Technology (NIST) (formerly the National Bureau of Standards (NBS)) issued the first botanical reference material certified for elemental content in January 1971, as Standard Reference Material (SRM) 1571, Orchard Leaves. In the following years a total of nine additional botanical certified reference materials have been issued by NIST. Each of these materials was certified for major, minor and trace elements except for SRM 2695, certified for fluorine only. Botanical SRMs issued since 1991 are significantly improved over previous materials in a number of ways. Probably the most significant change is the use of a jet-milling process to grind them to extremely fine particles. This has resulted in botanical SRMs with significantly improved homogeneity. These NIST reference materials are described with information on homogeneity, drying techniques and grit content.     

Consensus values for NIST biological and environmental Standard Reference Materials

The National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards or NBS) has produced numerous Standard Reference Materials (SRM) for use in biological and environmental analytical chemistry. The value listed on the “NIST Certificate of Analysis” is the present best estimate of the “true” concentration of that element and is not expected to deviate from that concentration by more than the stated uncertainty. However, NIST does not certify the elemental concentration of every constituent and the number of elements reported in the NIST programs tends to be limited. Numerous analysts have published concentration data on these reference materials. Major journals in analytical chemistry, books, proceedings and “technical reports” have been surveyed to collect these available literature values. A standard statistical approach has been employed to evaluate the compiled data. Our methodology has been developed in a series of previous papers. Some subjective criteria are first used to reject aberrant data. Following these eliminations, an initial arithmetic mean and standard deviation (S.D.) are computed from remaining data for each element. All data now outside two S.D. from the initial mean are dropped and a second mean and S.D. recalculated. These final means and associated S.D. are reported as “consensus values” in our tables. Received: 25 April 1997 / Revised: 24 July 1977 / Accepted: 25 July 1997     

Recent developments in food-matrix Reference Materials at NIST

Since 1996, the National Institute of Standards and Technology (NIST) has developed several 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, and SRM 2383 Baby Food Composite. Three additional materials--SRM 1946 Lake Superior Fish Tissue, SRM 2384 Baking Chocolate, and SRM 2385 Spinach--are in preparation. NIST also recently assigned values for proximate (fat, protein, etc.), individual fatty acid, and total dietary fiber concentrations in a number of existing SRMs and reference materials (RMs) that previously had values assigned for their elemental composition. NIST has used several modes for assignment of analyte concentrations in the food-matrix RMs, including the use of data provided by collaborating laboratories, alone and in combination with NIST data. The use of data provided by collaborating food industry and contract laboratories for the analysis of food-matrix RMs has enabled NIST to provide assigned values for many analytes that NIST does not have the resources or analytical expertise to measure.     

Cold neutron prompt gamma activation analysis at NIST: A progress report

An instrument for prompt gamma-ray activation analysis is now in operation at the NIST Cold Neutron Research Facility (CNRF). The cold neutron beam is relatively free of contamination by fast neutrons and reactor gamma rays, and the neutron fluence rate is 1.5·10⁸ cm^–2·s^–1 (thermal equivalent). As a result of a compact target-detector geometry the sensitivity is better by a factor of as much as seven than that obtained with an existing thermal instrument, and hydrogen background is a factor of 50 lower. We have applied this instrument to multielement analysis of the Allende meteorite and other materials.     

Intercomparison and determination of environmental standard samples by instrumental neutron activation analysis

To identify and improve the analytical technique for air pollution research, four kinds of environmental standard samples, i.e., airbome particulate matter, coal flyash, soil and pine needle supplied from the NIST and the IAEA were analyzed using thermal and epithermal neutron activation techniques. Sample irradiation was done at the irradiation facilities (neutron flux, 1 · 10¹³ n·cm^–2·s^–1) of the TRIGA MARK-III Research Reactor in the Korea Atomic Energy Research Institute. The accuracy and precision for the analysis of 40 trace and toxic elements in the samples were compared with the certified and reported values, respectively. In the analytical results of all standard reference materials, the relative standard deviation were within the 15% except for 11 elements and the relative error were agreed within the 10–20% except for 13 elements. The benefit of epithermal activation was investigated and the optimum analytical condition is reported.     

Particle size determination of some IAEA and NIST environmental and biological reference materials

Particle size distributions in fifteen International Atomic Energy Agency (IAEA) and sixteen National Institute of Standards and Technology (NIST) reference materials (RMs) were measured with the basic aim to investigate the potential of these materials to be used as reference or quality control materials in analyses where a small sample mass is required (< 100 mg). Most of the investigated materials are commercially available environmental or biological natural matrix RMs with certified values for trace elements, radionuclides, or organometallic compounds. The laser diffraction technique was used in all measurements. From the point of particle size distribution, materials IAEA-390 (Algae, a set of three materials), IAEA-396m (Urban Dust, 3x air jet milled), NIST-SRM 1515 (Apple Leaves), NIST-SRM 1547 (Peach Leaves), NIST-SRM 1566a (Oyster Tissue), NIST-SRM 1570a (Spinach), NIST-SRM 1573a (Tomato Leaves), and NIST-SRM 1648 (Urban Particulate) can be considered appropriate for small sample mass analysis. However, additional analytical tests are needed to confirm the appropriate homogeneous distribution of chemical composition, the level of heterogeneity for individual elements, at this sample mass level.     

Results of the ASTM Nuclear Methods intercomparison on NIST apple and peack leaves standard reference materials

The ASTM Task Group on Nuclear Methods of Chemical Analysis (E10.05.12) has conducted a trace element intercomparison among some of its members over the past two years. Eight non-NIST laboratories submitted data using nuclear techniques, with a total of 111 values for the apple leaves and 116 values for the peach leaves, on 46 and 50 elements, respectively. This intercomparison provided a unique opportunity for the analytical laboratories, because the analytical values submitted could be later compared to the NIST certified values. For the seven elements which were certified by NIST and had three or more intercomparison values, the results showed that: 1) 61% of all 56 intercomparison values submitted had results whose stated uncertainty overlapped the uncertainty limits of the NIST certified values, and 2) less than 6% of the intercomparison values had means which fell outside ±20% of the NIST values. In general, the intercomparison values submitted showed excellent agreement with the NIST values. However, many reported uncertainties accompanying intercomparison values appeared overly optimistic.     

Test of multielement analysis of bone samples using instrumental neutron activation analysis (INAA) and anti-Compton spectrometry

INAA and anti-Compton spectrometry has been employed in the analysis of test bone samples. Validity and accuracy of the method were checked by the use of two biological reference materials procured from the National Institute of Standards and Technology, USA (NIST) and the International Atomic Energy Agency, Austria (IAEA). NIST 1486 Bone Meal (ca. 200–800 mg) and A-11 Milk Powder (ca. 200–600 mg) samples were irradiated in the 100 kW TRIGA Mainz reactor. Concentrations of 13 elements in both biological reference materials have been determined and were found in good agreement with the certified and provisional values.     

Certification of a new NIST fly ash standard reference material

In June 1993 the National Institute of Standards and Technology (NIST) released the third version of Constituent Elements in Coal Fly Ash Standard Reference Material (SRM 1633b). This material is intended for quality assurance purposes in evaluating the analytical methods used for the determination of constituent elements in coal fly ash or in materials with similar matrices. It has been certified for 23 major, minor and trace elements using ten different analytical techniques. For an element to be certified in a NIST SRM, its concentration is usually determined by at least two independent analytical techniques. The concentrations of additional 24 elements are provided for information only purposes in the new fly ash. Current plans are to certify the concentrations of a number of rare earths upon completion of additional analytical work now in progress. Homogeneity testing was accomplished using instrumental neutron activation analysis and X-ray fluorescence. This presentation summarizes the preparation of this new material and the analytical results used for certification.     

Study on air pollution monitoring in Korea using instrumental neutron activation analysis

Trace elements in airborne particulate matter collected monthly at suburban and rural areas in Korea were analyzed by instrumental neutron activation analysis (INAA). Neutron irradiation of the samples was done at the irradiation hole (neutron flux 1·10¹³ n·cm^–2·s^–1) of the TRIGA Mark-III Research Reactor in the Korea Atomic Energy Research Institute. For the verification of the analytical technique, two reference materials, NIST SRM-1648 and NIES CRM-8, were chosen for analysis. The accuracy and precision of the determinations of the 40 elements were compared with the reference values. We used this method (1) to analyze 30 trace elements in airborne particulate matter collected monthly with the high volume air sampler (PM-10) at two different locations and (2) to confirm the possibility of using this method as a routine monitoring tool to find out environmental pollution sources.     

An interlaboratory characterization (certification) campaign to establish the elemental composition of a new series of agricultural/food reference materials

Summary Ten new Agricultural/Food Reference Materials (RM) have been characterized with respect to their elemental compositions in an extensive interlaboratory characterization (certification) campaign. The philosophy applied to determine best estimate and informational concentration values was the expert analyst-independent method approach. Chemical analyses were conducted in two initiating laboratories and by analysts in 73 cooperating laboratories applying 13 major classes of independently different analytical methods; approximately 13,000 results were obtained for a large number of nutritionally, toxicologically and environmentally pertinent elements. Results were assessed in depth using technical judgment and statistical criteria. A total of 213 best estimate values, with associated uncertainties for a single future observation, and 65 informational values were obtained. Concentrations were measured for 34 elements in 10 materials which represent a wide range of matrices and elemental contents and significantly augment the world repertoire of reference materials.Contribution no. 92–214 from Centre for Land and Biological Resources Research     

Improvements in the determination of vitamins in food through intercomparisons and preparation of RMs for vitamin analysis within the BCR1 programme

Summary In order to improve the methods for the determination of vitamins in food for nutritional purposes, the Commission's Community Bureau of Reference (BCR) has initiated a comprehensive research programme consisting of intercomparisons of methods to identify and eliminate sources of error and the preparation of reference materials (RMs). Six food RMs have been prepared to date including brussels sprouts, mixed vegetables and pigs' liver (all in the lyophilised form), vitamin enriched milk powder, wholemeal flour and margarine. The first five materials have been packaged into heat sealable, aluminium-laminate sachets under an inert atmosphere; margarine is a canned product. The initial homogeneity results have indicated no detectable signs of inhomogeneity for the vitamins/RMs investigated. Stability testing has monitored both short-term stability at elevated temperatures (+25 to 40°C, 8 weeks) and long-term stability –30 to +20°C, 36 months). The former was used to evaluate the effect of adverse shipment conditions on vitamin stability. Vitamins C and B₁, two of the more labile vitamins, have been found to be stable for up to 4 weeks at +25°C and 8 weeks at +37°C in brussels sprouts (RM 431) and wholemeal flour (RM 122), respectively.The results of long-term stability testing of vitamins C and B₁ in these RMs indicate there was no significant degradation of vitamin C in RM 431 for up to 24 months at –18 and +4°C when the data was expressed on the basis of the –30°C data (analytical control). Similarly, no significant degradation for vitamin B₁ in RM 122 was found at +4 and +20°C for up to 12 months, again after expressing the data on the basis of the analytical control (–20°C). Once acceptable homogeneity and stability results have been found, certification studies for each vitamin/RM are planned.     

Preliminary assessment of homogeneity of new candidate agricultural/food reference materials

Summary In an effort to bring to the analytical community new natural matrix reference materials (RM's) for elemental composition quality control, ten new agricultural/food candidate reference materials prepared previously, were characterized for homogeneity. The materials include bovine muscle powder, whole egg powder, corn bran, microcrystalline cellulose, wheat gluten, whole milk powder, corn starch and three wheat flours representing a wide range of matrix types and elemental composition. Characterization was for up to some twenty five major, minor, trace and ultratrace elements of nutritional, toxicological and environmental significance. Solid sampling electrothermal atomic absorption spectrometry was applied to the determination of copper and lead in sub-milligram subsamples. A variety of other analytical techniques via an interlaboratory cooperative effort was used to determine many other elements in 100–2000 mg subsample sizes. Good material homogeneity was observed for virtually all materials and analytes with the exception of Cr and Pb in limited instances. The materials were thus deemed suitable for detailed characterization of elemental concentration to lead to recommended values and to bring these biological products to reference material status.