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     

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.     

Three new mussel tissue standard reference materials (SRMs) for the determination of organic contaminants

Three new mussel tissue standard reference materials (SRMs) have been developed by the National Institute of Standards and Technology (NIST) for the determination of the concentrations of organic contaminants. The most recently prepared material, SRM 1974b, is a fresh frozen tissue homogenate prepared from mussels (Mytilus edulis) collected in Boston Harbor, Massachusetts. The other two materials, SRMs 2977 and 2978, are freeze-dried tissue homogenates prepared from mussels collected in Guanabara Bay, Brazil and Raritan Bay, New Jersey, respectively. All three new mussel tissue SRMs complement the current suite of marine natural-matrix SRMs available from NIST that are characterized for a wide range of contaminants (organic and inorganic). SRM 1974b has been developed to replace its predecessor SRM 1974a, Organics in Mussel Tissue, for which the supply is depleted. Similarly, SRMs 2977 and 2978 were developed to replace a previously available (supply depleted) freeze-dried version of SRM 1974a, SRM 2974, Organics in Freeze-Dried Mussel Tissue. SRM 1974b is the third in a series of fresh frozen mussel tissue homogenate SRMs prepared from mussels collected in Boston Harbor starting in 1988. SRM 1974b has certified concentration values for 22 polycyclic aromatic hydrocarbons (PAHs), 31 polychlorinated biphenyl congeners (PCBs), and 7 chlorinated pesticides. Reference values are provided for additional constituents: 16 PAHs, 8 PCBs plus total PCBs, 6 pesticides, total extractable organics, methylmercury, and 11 trace elements. PAH concentrations range from about 2 ng g^–1 dry mass (cyclopenta[cd]pyrene) to 180 ng g^–1 dry mass (pyrene). PCB concentrations range from about 2 ng g^–1 dry mass (PCB 157) to 120 ng g^–1 dry mass (PCB 153). The reference value for total PCBs in SRM 1974b is (2020 ± 420) ng g^–1 dry mass. Pesticide concentrations range from about 4 ng g^–1 dry mass (4,4-DDT) to 40 ng g^–1 dry mass (4,4-DDE). SRM 2977 has certified values for 14 PAHs, 25 PCB congeners, 7 pesticides, 6 trace elements, and methylmercury. Reference values for 16 additional PAHs and 9 inorganic constituents are provided, and information values are given for 23 additional trace elements. SRM 2978 has certified and reference concentrations for 41 and 22 organic compounds, respectively, and contains contaminant levels similar to those of SRM 1974b. Organic contaminant levels in SRM 2977 (mussels from Guanabara Bay, Brazil) are typically a factor of 2 to 4 lower than those in SRM 1974b and SRM 2978. The organic contaminant concentrations in each new mussel tissue SRM are presented and compared in this paper. In addition, a chronological review of contaminant concentrations associated with mussels collected in Boston Harbor is discussed as well as a stability assessment of SRM 1974a.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Characterization (certification) of Corn Bran (NIST RM 8433), Corn Starch (NIST RM 8432) and Microcrystalline Cellulose (NIST RM 8416) Reference Materials for essential and toxic major, minor and trace elemental constituents

Summary Corn Bran (NIST RM 8433), Corn Starch (NIST RM 8432) and Microcrystalline Cellulose (NIST RM 8416) Reference Materials were characterized for essential and toxic major, minor and trace elemental composition in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods by analysts in cooperating laboratories yielded 10–29 best estimate and 1–16 informational concentration values for each of these materials. Two materials, Corn Starch and Microcrystalline Cellulose, contain particularly low levels of trace elements. These reference materials are intended for analytical quality control of elemental determinations in corn and plant products as well as other agricultural/food materials with related matrices.Contribution No. 92–146 from Centre for Land and Biological Resources Research     

Reference material needs in clinical laboratory science

In 1968, clinical chemistry was considered to be the field most in need of certified reference materials (CRMs). While significant progress has been made in this area, new diagnostic assays are continually being developed that create a need for new CRMs. Members of the clinical laboratory community help to identify reference material needs. Professional and governmental organizations, such as IFCC, AACC, NCCLS, CDC, and the national metrological institutes (NMIs), respond to develop protocols and materials. Several measurands are presented as examples. In the late 1950s and early 1960s, in response to a need for standardization of lipid and lipoprotein measurements, CDC developed a reference system that included secondary reference materials. Over the years, the process of preparation of these materials was refined, eventually leading to the development of NCCLS guideline for preparation of commutable frozen serum pools for use as secondary reference materials (C37-A). This protocol was used for the preparation of NIST SRM 1951a (lipids in frozen (liquid) human serum). In the 1980s, a need for a reference material for blood lead was identified. CDC and NIST cooperated to develop SRM 955 (lead in bovine blood). More recently, efforts have been initiated to standardize high-sensitivity C-reactive protein (hsCRP) assays. In this case, a CRM for CRP existed (CRM 470, developed by IFCC and available from IRMM), but at concentrations in the acute phase reactant range and not in the low range needed for hsCRP assays. CDC coordinated a study to evaluate diluted CRM470 and other candidate materials as secondary reference materials for hsCRP assays.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, June 15–19, 2003, Berlin, Germany.     

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.     

Trace rare earth element analysis of IAEA Hair (HH-1), Animal Bone (H-5) and other biological standards by radiochemical neutron activation

A radiochemical neutron activation analysis using a rare earth group separation scheme has been used to measure ultratrace levels of rare earth elements (REE) in IAEA Human Hair (HH-1), IAEA Animal Bone (H-5), NBS Bovine Liver (SRM 1577), and NBS Orchard Leaf (SRM 1571) standards. The REE concentrations in Human Hair and Animal Bone range from 10^–8 g/g to 10^–11 g/g and their chondritic normalized REE patterns show a negative Eu anomaly and follow as a smooth function of the REE ionic radii. The REE patterns for NBS Bovine Liver and Orchard Leaf are identical except that their concentrations are higher. The similarity among the REE patterns suggest that the REE do not appear to be fractionated during the intake of biological materials by animals or humans.     

Neutronenaktivierungsanalytische Bestimmung des Chromgehaltes von Laboratoriumskaninchen-Skelettmuskel

Zusammenfassung Als Beitrag zur Ermittlung der richtigen Werte der Chromgehalte von menschlichen und tierischen Geweben und Körperflüssigkeiten wurde der Chromgehalt von Laboratoriumskaninchen-Skelettmuskel neutronenaktivierungsanalytisch bestimmt. Bisherige Angaben anderer Autoren: <7,1–121 ng/g. Die Verbesserung einer in der Literatur angegebenen ⁵¹Cr-Abtrennung durch Chromylchloriddestillation und die erforderlichen Maßnahmen zur Minimierung des Chromblindwertes werden beschrieben. Dessen Hauptanteil wird durch die Restverunreinigung der Bestrahlungsampullen-Oberfläche mit Chrom bedingt und beträgt 0,049 ng Cr (ohne Gefriertrocknung) bzw. 0.12 ng Cr (mit Gefriertrocknung). Analysen von Standardreferenzmaterialien (SRM) ergaben Chromgehaltswerte, die bei NBS-Citrus Leaves mit dem Zertifikatswert, bei IAEA animal muscle (H-4) mit dem neuesten Literaturwert von 9,2±2,5 ng/g übereinstimmen. Im Falle von NBS-Orchard Leaves erwies sich, daß dieses SRM für die Überprüfung der Methode ungeeignet ist. In Analysen von Oberschenkelmuskel-Proben von Bastardkaninchen resultierten Chromgehalte von 6,2–22,9 ng/g (bezogen auf Frischgewicht). Aus dem Vergleich dieser Daten mit dem früher gefundenen Wert von 1,2 ng/g, dem Literaturwert <7,1 ng/g und dem auf Frischgewicht berechneten H-4-Wert von 2,5 ng/g folgt, daß die Chromgehalte von Säugetier-Skelettmuskel innerhalb eines breiten Bereiches liegen dürften, auch die von Muskel einer Subspecies.

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Determination of the chromium content of laboratory rabbit skeletal muscles by neutron activation analysis

Summary The accurate values of the chromium contents of human and mammalian tissues and body fluids and appropriate procedures for their determination are still a matter of discussion. In this connexion, the chromium content of skeletal muscle of laboratory rabbits has been determined using neutron activation analysis. Data hitherto published by other authors: <7.1–121 ng/g. The procedure for separation of ⁵¹Cr by distillation of chromium oxychloride, described in the literature, has been improved. The arrangements necessary to minimize the chromium blank values are described. The main component of this blank is caused by the residual chromium contamination of the surface of the sample vial; typical values of this component are 0.049 ng Cr (without lyophilization) and 0.12 ng Cr (with lyophilization). The analyses of standard reference materials (SRM) yielded values of the chromium contents that are in agreement (i) with the certified value in the case of NBS Citrus Leaves, and (ii) with the latest published value of 9.2±2.5 ng/g in the case of IAEA animals muscle (H-4). NBS Orchard Leaves was found not to be an appropriate SRM for testing the method. In analyses of samples of thigh muscle of bastard rabbits chromium contents of 6.2–22.9 ng/g (fresh weight basis) were obtained. Comparison of these data with a previously found value of 1.2 ng/g, the literature value <7.1 ng/g and the value 2.5 ng/g for H-4 calculated on fresh weight basis indicated that the chromium contents of mammalian skeletal muscle might lie in a broad range, even for a subspecies.

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Herrn Prof. Dr. K. H. Lieser zum 65. Geburtstag gewidmet     

Testing the accuracy of neutron activation analysis of silver in biological materials

While silver can be efficiently collected from biological materials into lead beads by conventional fire assay, reagent blanks make this method unsuitable for determining the metal at concentrations less than 1 ppm. A radiochemical neutron activation analysis method is described which avoids this problem and can give reliable results down to 1 ng g^–1. The method has been tested using various reference materials /RM/, and it is concluded that NIES Mussel and Pepperbush are the best characterised RMs for determining traces of silver.     

Preparation and value assignment of standard reference material 968e fat-soluble vitamins, carotenoids, and cholesterol in human serum

Standard Reference Material 968e Fat-Soluble Vitamins, Carotenoids, and Cholesterol in Human Serum provides certified values for total retinol, γ- and α-tocopherol, total lutein, total zeaxanthin, total β-cryptoxanthin, total β-carotene, 25-hydroxyvitamin D₃, and cholesterol. Reference and information values are also reported for nine additional compounds including total α-cryptoxanthin, trans- and total lycopene, total α-carotene, trans-β-carotene, and coenzyme Q₁₀. The certified values for the fat-soluble vitamins and carotenoids in SRM 968e were based on the agreement of results from the means of two liquid chromatographic methods used at the National Institute of Standards and Technology (NIST) and from the median of results of an interlaboratory comparison exercise among institutions that participate in the NIST Micronutrients Measurement Quality Assurance Program. The assigned values for cholesterol and 25-hydroxyvitamin D₃ in the SRM are the means of results obtained using the NIST reference method based upon gas chromatography-isotope dilution mass spectrometry and liquid chromatography-isotope dilution tandem mass spectrometry, respectively. SRM 968e is currently one of two available health-related NIST reference materials with concentration values assigned for selected fat-soluble vitamins, carotenoids, and cholesterol in human serum matrix. This SRM is used extensively by laboratories worldwide primarily to validate methods for determining these analytes in human serum and plasma and for assigning values to in-house control materials. The value assignment of the analytes in this SRM will help support measurement accuracy and traceability for laboratories performing health-related measurements in the clinical and nutritional communities.     

Installation of Kayzero-INAA standardization in the TNRC and its applications for trace elements determination in different materials

The paper focuses on the validation of the k ₀-method of instrumental neutron activation analysis (k ₀-INAA) in the Tajura Nuclear Research Center (TNRC) via the analysis of several certified reference materials. The selected reference materials were: SRM 1572 Citrus Leaves, SRM 1575 Pine Needles, IAEA-A11 Milk Powder, IAEA-V-10 Hay Powder, RM IAEA-Soil-7 and RM IAEA-SL-1 Lake Sediment. The method is based on the PC version Kayzero/Solcoi software package issued by DSM. All the samples, reference materials and monitors were irradiated in various positions of the Tajura reactor with different f and α. The parameters f and α (f — thermal/epithermal neutron flux ratio, α — parameter accounting for the non-ideality of the 1/E epithermal neutron fluence rate distribution) were determined using the bare triple monitor method. The results obtained for all the reference materials are in good agreement with the certified values.     

Determination of cholesterol in serum using mass fragmentography — a reference method in clinical chemistry

Ohne Zusammenfassung

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Determination of cholesterol in serum using mass fragmentography — a reference method in clinical chemistry

     

Long-term stability of the elemental composition in biological materials

Summary Lyophilized and radiation sterilized biological certified reference materials (CRMs) are believed to be stable in their chemical composition. Generally, the certifying agencies consider the certificates of these biological CRMs valid for a 5-year shelf life, i.e., apart from measurable moisture content, the chemical composition should not change during that time. The long-term behavior of fresh frozen material is not known. In this study the elemental compositions of the Bovine Liver Standard Reference Material (SRM 1577) and human liver tissue samples are evaluated over a time period of more than 7 years. The concentrations of selected elements were determined by neutron activation analysis at various times. The initial evaluation of zinc, selenium and arsenic results gives no indication of changes during 7 years storage of fresh frozen tissues, however, a trend towards lower arsenic concentrations has been observed in SRM 1577 during a 10-year period.

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Langzeitstabilität der Elementzusammensetzung in biologischen Materialien

     

Preparation of twelve candidate agricultural reference materials

Summary A cost-effective approach to monitoring and maintaining reliability of analytical procedures is by the incorporation of appropriate, compositionally similar reference materials into the scheme of analysis. Agricultural and food commodities represent an extremely wide range of composition, in respect of the sought-for analyte and the supporting material (matrix), not fully reflected in currently available biological reference materials (BRM's). With the view to attempting to fill some of the gaps in the world repertoire of reference materials and to have suitable products for our laboratories' use, preparation has been completed of twelve candidate agricultural reference materials. These products, representing a number of food classes, include bovine muscle powder, hard red spring wheat flour, soft winter wheat flour, durum wheat flour, wheat gluten, corn bran, corn starch, potato starch, whole egg powder, whole milk powder, microcrystalline cellulose, and sugar. Preparative steps included, as required, freeze drying, grinding or ball milling, X-ray sterilization, sieving, blending and packaging to yield sizeable quantities of each material in finely powdered form. Cooperative analytical effort is expected to lead to characterization in respect of concentrations of a number of nutritionally, toxicologically and environmentally-pertinent, major, minor, and trace chemical elements. These materials will then be available for analytical chemical data quality control for inorganic constituents in a range of agricultural commodities.

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Herstellung von zwölf als landwirtschaftliche Referenzmaterialien vorgeschlagenen Substanzen

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Contribution No. 88-49 from Land Resource Research Centre     

Nouvelles substances d'intercomparaison proposees pour l'etalonnage en temperature et en energie d'analyseurs thermiques (ou calorimetriques) differentiels

Several organic compounds as new reference materials for temperature and energy calibration of DTA and DSC appartuses were studied in the range of temperature 300–600 K.

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Zusammenfassung Im Temperaturbereich 300–600 K wurden einige organische Verbindungen als neue Referenzsubstanzen für die Temperatur- und Energieeichung bei DTA und DSC untersucht.

     

Determination of selenium by hydride generation with reducing tube followed by graphite furnace atomic absorption spectrometry

Summary Selenium was determined in biological samples (tea and bovine liver, NBS, SRM 1577) by a combination of hydride generation with reducing tube, graphite furnace atomization and atomic absorption detection. The selenium was reduced by a pellet of sodium borohydride which was placed in a horizontal glass tube. 1.6–2.0 l/min of argon flow rate and 2400° C of atomization temperature were the best experimental conditions. Copper produces a severe effect on absorbance, even if present in only 2 times the amounts of selenium. Ion-exchange resin (Dowex 50 W-X8) was used for the separation of Cu, Ni and Co. A detection limit of 1 ng was obtained with a precision of 5–6%.

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Selenbestimmung durch Hydriderzeugung im Reduktionsrohr mit nachfolgender Graphitofen-AAS

Zusammenfassung Durch Kombination von Hydriderzeugung und Graphitofen-AAS wurde Selen in biologischen Proben (Tee, Rinderleber, NBS, SRM 1577) bestimmt. Die Reduktion erfolgte durch Natriumborhydrid in einem horizontalen Glasrohr. 1,6–2,0 l/min Argon und 2400° C Atomisierungstemperatur erwiesen sich als optimal. Kupfer übt selbst bei nur doppelter Menge einen störenden Einfluß aus. Zur Abtrennung von Cu, Ni und Co wurde ein Ionenaustauscher (Dowex 50W-X8) verwendet. Die Nachweisgrenze beträgt 1 ng bei einer Reproduzierbarkeit von 5–6%.

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Paper read at the meeting of 9th ICAS/XXII CSI, Tokyo, September 1981     

Determination of copper in powdered chocolate samples by slurry-sampling flame atomic-absorption spectrometry

Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L^–1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L^–1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 g g^–1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 g g^–1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 g g^–1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.     

Homogeneity studies in reference materials with Zeeman solid sampling GFAAS

Summary The homogeneity of lead and cadmium in reference materials was investigated by solid sampling GFAAS. The following materials were comparatively analyzed: Standard reference materials from NBS, Washington 1567 Wheat flour, 1568 Rice flour and 1577a Bovine liver, certified reference materials from BCR, Brussels, No 63 Milk powder, No 184 Bovine muscle, No 185 Bovine liver, No 186 Pig kidney, No 189 Wholemeal flour, No 191 Brown bread and a whole fish (dab) homogenate from the environmental specimen bank in the FRG. The results are remarkably different for the investigated materials.

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Homogenit?tsstudien in Referenzmaterialen mit Zeeman-Feststoff-GFAAS

     

Determination of As,Cd, Hg,Cu and Zn in biological samples by radiochemical neutron activation analysis

In this work, a simple group separation scheme based on extraction for NAA determination of trace of As, Cd, Hg, Cu and Zn in biological materials is described. For this purpose, zinc-diethyldithiocarbamate, Zn(DDC)₂, and methyl isobutyl ketone-iodide have been chosen as reagents. The elements can be extracted successively and quantitatively from strong mineral acids without adjusting pH of the solution, and separated into two groups suitable for gamma-ray spectrometry. Samples of 100–200 mg dry weight were double-sealed into polyethylene bags and irradiated in a swimming pool reactor with a thermal neutron flux of 10¹³n·cm^–2·s^–1 for 44 hours. After a cooling period of 1–3 days, the samples were digested with microgram quantities of carrier in concentrated nitric acid and sulfuric acid at 150°C for 3.5 hours in a teflon bomb, then extracted as described above. The reliability of the analytical method was checked using reference materials Horse Kidney IAEA H-8, Human Hair NIES-5 and Tomato Leaves NBS-1573. Most of the results obtained for reference materials agreed with the certified values¹². Chinese autopsy samples of hair and liver were presented.