Kinetic speciation of BCR reference materials

The accurate study of heavy metal speciation is important in environmental monitoring. There has been much work developing various operationally defined speciation methods for soil and sediment, but there is a need to compare the different approaches by evaluating them for the same sample. In this article, a kinetic method was applied for the heavy metal speciation of the two BCR reference materials, CRM601 and BCR701, which have been specifically developed as materials to evaluate the validated BCR three-step sequential extraction method. When EDTA was used as an extractant, 81.0% of Cd, 68.0% of Cu, 21.5% of Ni, 80.3% of Pb and 71.9% of Zn was extracted from CRM601. For BCR701, the removal ratios were 92.0, 52.3, 18.7, 50.6 and 67.5% with EDTA and 95.7, 25.2, 20.0, 52.4 and 68.5% with hydroxylamine hydrochloride as an extractant, for Cd, Cu, Ni, Pb and Zn respectively. A two-component kinetic model was applied to the extraction curve and the extractable metals were readily classified into two categories, namely, labile fraction and non-labile fractions. The rate constants obtained from the regression model were found to be useful in quantifying the lability of an element. The rate constants obtained from the labile fractions in BCR701 were higher than that of obtained from CRM601, which indicated the high lability of metals in BCR701. When compared with the sequential extraction data, it seemed that the lability of an element was positively correlated to the first step extraction fraction.     

Antioxidant analysis in edible oils and fats by normal-phase high-performance liquid chromatography

Following a simple dilution in the appropriate phase, the sample is injected directly onto either of two normal-phase high-performance liquid chromatography systems (3,5-di-tert.-butyl-4-hydroxytoluene or 3-tert.-butyl-4-hydroxyanisole-tert.-butylhydroquinone) with UV detection at 280 nm. An isocratic ternary mobile phase, incorporating acetonitrile as the polar modifier, has been found to facilitate such an approach, thereby avoiding the discriminatory and recovery problems inherent in other techniques requiring prior sample manipulations. The three most commonly used antioxidants may be estimated at levels down to 3 ppm (3,5-di-tert.-butyl-4-hydroxytoluene or 3-tert.-butyl-4-hydroxyanisole) and 10 ppm (tert.-butylhydroquinone) within 30 min.     

Enthalpimetric determination of the iodine value of some edible oils and fats

A simple, rapid and accurate direct injection enthalpimetric (DIE) method has been developed for the determination of the iodine value of some commercial edible oils. A significant heat pulse of halogen addition reaction of the double bonds of unsaturated fatty acid esters in the oils is produced by injecting a solution of iodine monochloride into the sample solutions. The method is calibrated against real samples and the standard compounds (oleic, linoleic and linolenic acids) whose iodine values have been determined by a standard method. Once calibrated, the proposed method can be operated routinely by semi-skilled personnel. The method is sensitive and give results as acceptable as those obtained by standard methods. The main advantages of the method are those of time and cost of analysis and the potential of the enthalpimetric method for automation.

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Zusammenfassung Zur Ermittlung der Jodzahl von einigen im Handel befindlichen Speiseölen wurde ein einfaches, schnelles und genaues Enthalpimetrieverfahren mit Direkteinspritzung (DIE) entwickelt. Mittels Einspritzung einer Jodmonochloridlösung in die Probenlösung wird wegen der Halogenadditionsreaktion an den Doppelbindungen der ungesÄttigten FettsÄureester ein signifikanter WÄrmeimpuls erzeugt. Die Methode wird anhand tatsÄchlicher Proben und Standardproben (ölsÄure, LinolsÄure, LinolensÄure) kalibriert, deren Jodzahl in Standardverfahren bestimmt wurde. Nach einmaliger Kalibration kann das Verfahren auch von angelerntem Personal routinemÄ\ig durchgeführt werden. Das Verfahren besitzt eine ausreichende Empfindlichkeit und liefert Ergebnisse, die genauso akzeptabel sind, wie die in Standardverfahren erhaltenen Ergebnisse. Die Hauptvorteile dieser Methode bestehen in Zeit- und Kosteneinsparung bei der Analyse sowie in der Möglichkeit, das enthalpimetrische Verfahren automatisieren zu können.

     

BCR certified reference materials for reactor neutron dosimetry

A series of reference materials intended for use as activation or fission monitors for neutron fluence rate measurements has been prepared by the Joint Research Centre of the European Commission. Certification has been carried out by expert European laboratories and distribution of the certified reference materials (CRMs) is through the BCR programme of the Commission. The list (18 CRMs) includes materials to cover the complete energy spectrum, and suitable for different irradiation times. Fission monitors are ²³⁸UO₂ or ²³⁷NpO₂ in the form of microspheres. Activation monitors are high purity metals (Ni, Cu, Al, Fe, Nb, Rh, or Ti), certified for interfering trace impurities, or dilute aluminium-based alloys, where aluminium is chosen as a suitable matrix for reducing the neutron self-shielding effect. Newly certified materials are IRMM-530R Al-0.1%Au, replacing the exhausted IRMM-530 material, used as comparator for k ₀-standardization, and three new Al-Co alloys (0.01-1%Co). Two others, in the process of certification are Al-0.1%Ag and Al-2%Sc for thermal and epithermal fluence rate measurements. Other candidate reference materials currently being certified are two uranium-doped glass intended for dosimetry by the fission-track technique.     

Polycyclic aromatic hydrocarbons in edible fats and oils: occurrence and analytical methods

This review deals with analytical methods for polycyclic aromatic hydrocarbon (PAH) determination in oils and fats. The data reported in the introduction deal with PAH dietary intake from this group of food and contamination levels recently found by some authors in different vegetable oils, stressing the importance of establishing a method suitable for routine analyses. Traditional sample preparation relies on tedious, time-consuming procedures. They generally consist of an extraction step (liquid-liquid partition, caffeine complexation, saponification) followed by one or more purification procedures (column chromatography, thin-layer chromatography, solid-phase extraction). The analytical determination is usually carried out by HPLC and spectrofluorometric detection, or through high-resolution capillary GC coupled to flame ionisation detection or mass spectrometry. LC is a valid alternative to the traditional sample preparation, and off-line LC-LC allows performing an accurate PAH analysis in less than 2 h. Also supercritical fluid extraction, allowing performing both extraction and clean-up in one combined step, is a promising technique. Hyphenated techniques such as LC-GC and LC-LC-GC seem to be very promising. A completely on-line method for alkylated PAH determination in oils or lipidic extracts contaminated with mineral oil involves a two-dimensional LC-step with intermediate eluent evaporation and GC transfer through a vaporiser/overflow interface.     

Determination of specific heats of some edible oils and fats by differential scanning calorimetry

Measurements of specific heat as a function of temperature were carried out with a differential scanning calorimeter on rape-seed, soybean, sunflower and corn oils and on lard.

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Zusammenfassung Es wurden Messungen der spezifischen Wärme als Funktion der Temperatur von Raps-, Soia-, Sommerblumen- und Mais-ölen und von Schmalz mit Hilfe von einem Dynamische-Differenz-Kalorimeter durchgeführt.

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BCR reference materials for food and agricultural analysis: an overview

Summary The BCR is a research programme of the European Communities having the broad aim of improving accuracy and measurement harmony in areas of concern at Community level. Much of the work is directly relevant to the removal of trading and other obstacles as is necessary for the achievement of a single European market by 1992.The presentation provides an overview of the sector of the programme concerned with Reference Materials (RMs) for food and agricultural analyses.Summarises are given of activities for inorganic, trace organic and nutritional analyses, for calibration of rapid methods (NMR, NIR, XRF and Immuno-assay techniques) and technological measurements (industrial quality of cereals, food colour, water-sorption and detection of fraudulent addition of sugar during wine making by NMR). An alphabetic listing of analytes and properties studied during the programme is given.

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BCR-Referenzmaterialien für die Lebensmittel- und landwirtschaftliche Analyse — Ein Überblick

     

The determination of phenolic anti-oxidants in edible oils and fats by high-performance liquid chromatography

A simple procedure for the extraction of phenolic anti-oxidants with methanol is described. The extracted compounds are determined by gradient elution with retention times of 4.0–13.2 min; an internal standard technique is used for quantification.     

BCR (non-certified) reference materials for dioxins and furans in milk powder

Milk powders spiked with different quantities of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) have been prepared by both freeze drying and spray drying. In 1991, the freeze dried batches were used in a BCR intercomparison. The spray dried batches have now been compared to the freeze dried ones. The obtained results show that:

-there is no significant difference between the materials;

-the recoveries of the added amounts of D48, D54, D66, D67, D70, F83, F94, F114, F118, F121 and F130 are of the order of 90%.

On this basis, assigned values are proposed for the spray dried materials which will become available as a set of three (non-certified) BCR reference materials (RM 532, RM 533, RM 534).     

微波消化-石墨炉原子吸收法测定食用油脂中的铜

用微波消化技术对各种食用油脂试样进行预处理，针对样品特性，优化较佳的微波消化条件与操作参数，建立了用微波消化－石墨炉原子吸收法测定食用油脂中的铜，减少了样品处理过程中的损失，回收率为92.4%-96.2%；RSD为3.0%-3.6%, 检出限为0.05mg/kg。     

GC-MS法鉴别食用油和餐饮业中废弃油脂的研究

用气相色谱 质谱联用(GC MS)方法对7种餐饮业中废弃油脂(简称废油脂)和5种合格成品食用油(简称食用油)中所有脂肪酸进行分析。研究发现,废油脂中部分不饱和脂肪酸受到氧化,使脂肪酸相对不饱和度(U R)值明显小于同种类食用油中的脂肪酸相对不饱和度(U R)值,其脂肪酸的质量分数分布与同种类的食用油中脂肪酸的质量分数分布有很大的区别,以及绝大部分废油脂中存在较大量矿物油。研究表明,脂肪酸相对不饱和度(U R)值和脂肪酸的质量分数分布可以鉴别废油脂。     

Optimized analysis oftrans-octadecenoic acids in edible fats

Summary Trans fatty acids (TFA) in edible fats are of interest, since they are suspected to influence serum lipid levels. Thus, to estimate the atherogenic potency of edible fats a precise analytical method for the determination of TFA is required. The present study does not only aim at the quantitative analysis of total C18:1 TFA, but also at the determination of the isomeric pattern oftrans-octadecenoic acids in different fats. The combination of argentation TLC with high resolution gas chromatography allows the quantification of 10trans- and 9cis-octadecenoic acid peaks. This method can be applied to hydrogenated vegetable fats as well as to ruminant fats and tissue lipids from different species. Based on this two-dimensional chromatography the intake of single TFA isomers with food can be determined, which is of importance with respect to the hypothesis, that the negative metabolic activity originates only from certain isomers, and to the considerable variation of isomeric patterns in different edible fats. Based on the precise determination of the totaltrans-octadecenoic acid content in milk fats by TLC and GC, a formula has been derived by regression analysis, which allows the evaluation of total C18:1 TFA contents from a routine GC analysis. Though the 61 milk fats used covered a wide scope of feeding and lactation conditions, a correlation coefficient of 0.9991 was achieved.     

Comprehensive two-dimensional liquid chromatography x gas chromatography: evaluation of the applicability for the analysis of edible oils and fats

Edible fats and oils are complex mixtures containing a wide range of (classes of) compounds. The most important group of compounds are the triglycerides (triacylglycerides, TAGs). Because of the large number of possible fatty acid combinations, an enormous number of TAGs is possible. In the present feasibility study, the applicability of different modes of comprehensive two-dimensional LCXGC for detailed oil and fat analysis is evaluated. Comprehensive LCXGC was found to be an extremely powerful analytical method for the analysis of complex TAG samples. Using the new comprehensive set-ups, TAGs can be separated according to two independent parameters: carbon number vs. number of double bonds, or fatty acid composition vs. number of double bonds. The information content of comprehensive separations by far exceeds that of the current generation of analytical methods. The quantitative results of the separations show a good agreement with data obtained from standard analytical methods. The comprehensive methods studied can also be used for fingerprinting of oil samples, as well as for the analysis of target compounds or compound groups. Highly detailed separations of olive oil samples were obtained. Zooming in on one region of the chromatogram allowed reliable analysis of wax esters without interferences of sterol esters.     

Lipophilicity of oils and fats estimated by TLC

A representative series of natural toxins belonging to alkaloids and mycotoxins classes was investigated by TLC on classical chemically bonded plates and also on oils‐ and fats‐impregnated plates. Their lipophilicity indices are employed in the characterization and comparison of oils and fats. The retention results allowed an accurate indirect estimation of oils and fats lipophilicity. The investigated fats and oils near classical chemically bonded phases are classified and compared by means of multivariate exploratory techniques, such as cluster analysis, principal component analysis, or fuzzy‐principal component analysis. Additionally, a concrete hierarchy of oils and fats derived from the observed lipophilic character is suggested. Human fat seems to be very similar to animal fats, but also possess RP‐18, RP‐18W, and RP‐8.     

Comprehensive two-dimensional liquid chromatography×gas chromatography: evaluation of the applicability for the analysis of edible oils and fats

Edible fats and oils are complex mixtures containing a wide range of (classes of) compounds. The most important group of compounds are the triglycerides (triacylglycerides, TAGs). Because of the large number of possible fatty acid combinations, an enormous number of TAGs is possible. In the present feasibility study, the applicability of different modes of comprehensive two-dimensional LC×GC for detailed oil and fat analysis is evaluated. Comprehensive LC×GC was found to be an extremely powerful analytical method for the analysis of complex TAG samples. Using the new comprehensive set-ups, TAGs can be separated according to two independent parameters: carbon number vs. number of double bonds, or fatty acid composition vs. number of double bonds. The information content of comprehensive separations by far exceeds that of the current generation of analytical methods. The quantitative results of the separations show a good agreement with data obtained from standard analytical methods. The comprehensive methods studied can also be used for fingerprinting of oil samples, as well as for the analysis of target compounds or compound groups. Highly detailed separations of olive oil samples were obtained. Zooming in on one region of the chromatogram allowed reliable analysis of wax esters without interferences of sterol esters.