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     

Summary of preparation and homogeneity characterization of ten agricultural food reference materials for elemental composition

Summary Preparation and development has been completed of ten agricultural/food reference materials (RMs): bovine muscle powder, corn starch, hard red spring wheat flour, soft winter wheat flour, whole milk powder, wheat gluten, corn bran, durum wheat flour, whole egg powder and microcrystalline cellulose. Homogeneity tests for 14 elements, Al, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr and Zn were performed by the initiating laboratories by application of precise and reliable analytical methods based on flame atomic absorption spectrometry and graphite furnace atomic absorption spectrometry. An extensive set of analytical results obtained from the interlaboratory cooperative characterization campaign was assessed to provide homogeneity estimates for other elements. Estimates of homogeneity from within-laboratory precision indicated that all materials exhibited acceptable homogeneity for virtually all 29 elements (Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cu, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Se, Sr, V, Zn) for which best estimate concentration values are available. Two thirds of all homogeneity coefficients of variation were below 5%.     

Preparation and homogeneity characterization of ten agricultural/food reference materials for elemental composition

Summary Ten agricultural/food reference materials (RM): bovine muscle powder, corn starch, hard red spring wheat flour, soft winter wheat flour, whole milk powder, wheat gluten, corn bran, Durum wheat flour, whole egg powder and microcystalline cellulose, were prepared by milling, irradiation, sieving, blending and packaging procedures. Homogeneity tests for 14 elements in randomly selected units were performed by the initiating laboratories by application of various analytical methods. Al, Ca, Cu, Fe, K, Mg, Mn, Na, Sr and Zn were determined by acid digestion flame atomic absorption spectrometry, and Cd, Co, Ni and Pb using acid digestion graphite furnace atomic absorption spectrometry after separation/preconcentration of the analytes by co-precipitation. In addition, the extensive set of analytical results obtained from the interlaboratory cooperative characterization campaign was assessed to provide homogeneity estimates for other elements. Measures of homogeneity were estimated from the within-laboratory precision from the more precise laboratories. All materials exhibited acceptable homogeneity for virtually all 29 elements (Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cu, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Se, Sr, V, Zn) for which best estimate concentration values were available, an essential pre-requisite in establishing reference values for these materials. Sixty-two percent of all homogeneity coefficients of variation (CV) were below 5%, with Br, Ca, Cl, Mg, Na, P, Zn and especially K and N exhibiting very high homogeneity CV less than 1% in some cases.Contribution no. 92–148 from Centre for Land and Biological Resources Research     

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.     

Beitrag zur Optimierung der chelat-gas-chromatographischen Berylliumbestimmung in organischen Matrices bei begrenzter Einwaage

Zusammenfassung Es wurden Techniken ausgearbeitet zur chelat-gas-chromatographischen Bestimmung von Berylliumspuren in verschiedenen organischen Matrices (Blut, menschliches und tierisches Gewebe, Nahrungsmittel, Abwasserschlämme u. a.) über Be-Trifluoracetylacetonat (Be-TFA) mit einem Elektroneneinfangdetektor (ECD). Die einzelnen Verfahrensschritte wurden radiochemisch mit⁷Be überprüft und optimiert: der Aufschluß der Probe mit angeregtem Sauerstoff (Mikrowellenfeld) oder mit Salpetersäure/Flußsäure unter Druck im Teflongefäß; die Entfernung der Störelemente; die Bildung des Be-TFA-Komplexes und das Ein engen der benzolischen Be-TFA-Lösung. Die kleinste mit diesem Verfahren nachweisbare Berylliummenge liegt für Proben 1 g bei 10^–11 g.

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Contribution to the optimization of the chelate gas-chromatographic determination of beryllium in limited amounts of organic materials

Suitable techniques for the chelate gas-chromatographic determination of beryllium traces in different organic materials (e.g. blood, human and animal tissue, food, sewage muds) were developed. An electron-capture detector (ECD) was used for the detection of Be-trifluoracetylacetonate (BeTFA). The individual steps of the procedure were optimized by the tracer method with⁷Be: low temperature ashing or pressure decomposition with nitric acid/hydrofluoric acid in a teflon tube, the elimination of interfering elements, the formation of the Be-TFA and the concentration of the Be-TFA solution. For samples 1 g the minimum detectable amount is 10^–11g.

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Herrn Prof. Dr. F. Straßmann, Mainz, zum 70. Geburtstag gewidmet.

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Wir danken der DFG (Sonderforschungsbereich 82, Universität Stuttgart), dem Wirtschaftsministerium von Baden-Württemberg, Stuttgart, und der DECHEMA, Frankfurt, für großzügige Unterstützung durch Personal- und Sachmittel.     

Ion-implanted reference standards for use in microchemical analysis of materials

Summary A concise overview has been given of the present state of development of ion-implanted reference standards for the calibration of instrumental methods of microchemical characterization of solid materials.

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Ionen-implantierte Standardpräparate für die Mikroanalyse

Zusammenfassung Der gegenwärtige Entwicklungsstand ionenimplantierter Standardpräparate für die Eichung instrumenteller Mikromethoden der chemischen Feststoffanalyse wurde besprochen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Development of food reference materials for nutritional analysis

Summary The development of five reference materials for major nutritional properties, whole milk powder, pork muscle, wheat and rye flour, and haricots verts beans is described. Homogeneity and stability of these materials proved to be adequate. A preliminary intercomparison of methods showed that results for total fat and total dietary fibre were method dependent. Evaluation of methods used for available carbohydrates revealed poor solubilisation and hydrolysis of starch in some laboratories. This intercomparison has given valuable information for the final certification of these materials.     

Gas-chromatographische Bestimmung von Vitamin E in Futter- und Lebensmitteln

Zusammenfassung Zur quantitativen Bestimmung von Vitamin E in Futter- und Lebensmitteln wird eine gas-chromatographische Methode beschrieben, die noch den Nachweis von 1 ng -Tocopherol gestattet. Nach Verseifung des Untersuchungsmaterials mit äthanolischer Kalilauge, Extraktion des Vitamins mit Diäthyläther und säulen-chromatographischer Reinigung kann das Vitamin E mit einer Genauigkeit von ±1.1% relativ gas-chromatographisch bestimmt werden.

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Gas-chromatographic determination of vitamin E in feedstuffs and food

A gas-chromatographic method for the determination of vitamin E in feedstuffs and food is described, which permits the detection of 1 ng of -tocopherol. After saponification of the material with methanolic potassium hydroxide, extraction of the vitamin with diethyl ether and column-chromatographic purification, the vitamin can be determined with an accuracy of ±1.1%.

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Herrn J. Heinrich wird für die gewissenhafte Mithilfe bei der Ausführung der Analysen gedankt.Die Arbeit wurde mit Unterstützung der Deutschen Forschungsgemeinschaft durchgeführt.     

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

     

Direct analysis of inorganic solids: Experiences of a laboratory in cement industries

Summary A report is given on the successful application of direct ZAAS as a trace-analytical tool for inorganic materials characteristically occurring in cement industries. Results of interlaboratory studies and analysis of standard reference materials for important elements as As, Cd, Cr, Hg, Tl and others are discussed in detail.Examples show that trace analysis directly from the solid is often successful using aqueous solutions for calibration. Characteristic interferences of direct ZAAS could normally be eliminated by admixture of graphite powder.

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Direkte Feststoffanalyse von anorganischen Materialien: Erfahrungsbericht aus einem Labor der Zementindustrie

Zusammenfassung Es wird über den erfolgreichen spurenanalytischen Einsatz der direkten ZAAS an für die Zementindustrie characteristischen anorganischen Proben berichtet. Dabei stehen die Ergebnisse von Ringversuchen und die Analyse von Standardreferenzmaterialien für so wichtige Elemente wie As, Cd, Cr, Hg, Tl und anderen im Mittelpunkt der Untersuchungen.Anhand von Beispielen wird gezeigt, daß die direkte Spurenbestimmung aus dem Festkörper häufig mit wäßrigen Bezugslösungen erfolgreich durchgeführt werden kann. Charakteristische Störungen der Direkten ZAAS konnten in der Regel durch Graphitbestimmungen beseitigt werden.

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Lecture given at the colloquium on the Analysis of Solids by AAS, Wetzlar, 8.–10. 10. 1984     

Nachweis und Bestimmung wasserl?slicher, synthetischer Lebensmittel-Farbstoffe mit Hilfe von Polyamidpulver

Zusammenfassung Es wird ein allgemein anwendbares Verfahren zur Anreicherung synthetischer, wasserlöslicher, in der BRD zugelassener Lebensmittel-Farbstoffe beschrieben. Aktives Polyamidpulver adsorbiert aus wäßriger oder wäßrigalkoholischer Lösung schnell quantitativ die Farbstoffe, die unter schonenden Bedingungen wieder desorbiert werden, so daß nach diesem Verfahren eine Bestimmung der zum Färben verwendeten Farbstoffmenge möglich ist. Ein unterschiedliches Adsorptionsverhalten von Polyamid verschiedener Herkunft gegenüber den Farbstoffen wurde festgestellt.

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Summary A generally applicable procedure has been described for the enrichment of synthetic, water-soluble food dyes, permitted in Germany (Federal Republic). Active polyamide powder adsorbs the dyes rapidly and quantitatively from aqueous or aqueous-alcoholic solution. The dyes can be eluted under mild conditions, so that the determination of the amount of dye used for coloration is possible. Polyamides of different provenance showed different adsorption properties for the dyes.

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Herrn Prof. Dr. B.Eistert zum 65. Geburtstag in Verehrung gewidmet.

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I. Mitteilung; technische Mitarbeit M.Bernau und J.Gruschke.

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Den Herren Prof. Dr. O.Neunhoeffer und B.Eistert danken wir für ihr Interesse an dieser Arbeit undfür wertvolle Diskussionen, der Deutschen Forschungsgemeinschaft für die Überlassung von Vergleichsmustern der Lebensmittel-Farbstoffe.     

NBS activities in biological reference materials

Summary NBS activities in biological reference materials during 1986–1988 are described with a preview of plans for future certifications of reference materials. During the period, work has been completed or partially completed on about 40 reference materials of importance to health, nutrition, and environmental quality. Some of the reference materials that have been completed during the period and are described include: creatinine (SRM 914a), bovine serum albumin (SRM 927a), cholesterol in human serum (SRM's 1951–1952), aspartate aminotransferase (RM 8430), cholesterol and fat-soluble vitamins in coconut oil (SRM 1563), wheat flour (SRM 1567a), rice flour (SRM 1568a), mixed diet (RM 8431a), dinitropyrene isomers and 1-nitropyrene (SRM 1596), and complex PAH's from coal tar (SRM 1597). Oyster tissue (SRM 1566a) is being analyzed and should be available in 1988.

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NBS-Aktivitäten in biologischen Referenzmaterialien

     

Berechnung des Gehaltes an Einzelkomponenten und deren Vertrauensintervalle im Falle der indirekten Analyse

Ohne Zusammenfassung

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Calculation of the content of individual components and their confidence intervals in indirect analysis

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Diese Arbeit kann im Zusammenhang mit unseren vorangehenden Beiträgen [1–3] über das Vertrauensintervall von Analysenergebnissen gesehen werden     

Anf?rbung von Aminos?uren mit Metallsalz-Ninhydrin-Gemischen

Zusammenfassung Der Einfluß verschiedener Metallionen auf die Anfärbbarkeit einer Reihe von Aminosäuren mit Ninhydrin wurde überprüft. Es ergab sich, daß die Farben des gesamten Spektrums, von blau über grün und gelb bis rot entstehen.

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Summary The influence of different metal ions on the colour produced by action of ninhydrin on several amino acids has been investigated. It has been shown that colours of the whole spectrum are formed, from blue via green and yellow to red.

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Auszugsweise vorgetragen auf dem V. Internationalen Symposium des Quedlinburger Arbeitskreises für Eiweißanalytik vom 27.–29. Oktober 1966.     

Iodine determination in food by inductively coupled plasma mass spectrometry after digestion by microwave-induced combustion

Iodine determination in food samples was performed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion by microwave-induced combustion (MIC). Sample masses up to 500 mg of bovine liver, corn starch, milk powder, or wheat flour were completely combusted using the MIC system. Ammonium nitrate (6 mol l⁻¹ solution, 50 μl) was used as an aid for ignition and vessels were charged with 15 bar of O₂. The use of H₂O, 0.9 mmol l⁻¹ H₂O₂, 10 to 50 mmol l⁻¹ (NH₄)₂CO₃ and 56 mmol l⁻¹ tetramethylammonium hydroxide was investigated as absorbing solutions, as well as the suitability of performing a reflux step after the combustion process. Digestion of food samples by pressurized microwave-assisted acid digestion, microwave-assisted extraction and conventional extraction of iodine in alkaline solution were also evaluated. Iodine recoveries higher than 99% were obtained using MIC and 50 mmol l⁻¹ (NH₄)₂CO₃ or 56 mmol l⁻¹ tetramethylammonium hydroxide as absorbing solution and with 5 min for the reflux step. Accuracy was evaluated using certified reference materials (bovine muscle, corn bran, and milk powder) and agreement better than 97% was obtained. The limit of quantification by MIC and further ICP-MS determination was 0.002 μg g⁻¹. Blanks were always low and no memory effects were observed. Digestion by MIC allowed the processing of up to eight samples by each run in 25 min with high efficiency of digestion (residual carbon content lower than 1%) providing a suitable medium for further iodine determination by ICP-MS.