Preliminary homogeneity study of in-house reference material using neutron activation analysis and X-ray fluorescence

Summary Although many biological reference materials for quality control of trace element analysis are commercially available, there is still a need for additional local materials for special matrices. In the Latin American region a preliminary study has been commenced involving analytical strategies for the characterization of in-house reference material. A biological sample, prepared in Brazil, constitutes the first regional attempt to prepare reference material. It was analyzed by neutron activation analysis (NAA) and X-ray fluorescence (XRF) to verify its homogeneity. The determination of the trace elements and certain major elements was carried out by instrumental NAA. Trace elements such as Cd, Mn, Mo and Cu were determined using NAA with radiochemical separations to improve the sensitivity and precision. XRF was applied only to major constituents and some trace elements with concentration of more than 10 g/g. From a total of 18 elements analyzed, only Fe, Cr and Sc were not homogeneously distributed.     

Collection, preparation and characterization of fresh, marine candidate reference materials of the German Environmental Specimen Bank

Summary The Environmental Specimen Bank (ESB) of the Federal Republic of Germany has been collecting and preparing specially selected biological reference materials since 1982 to help to control representative ecosystems. The preparation and homogenization of the sample material is carried out at cryogenic temperatures, below minus 150°C. There is a broad palette of fresh candidate RMs, stored at the ESB Jülich, characterized not only for special trace elements and essential bulk elements but also for polycyclic aromatic hydrocarbons (PAH) and chlorinated hydrocarbons (CHC). Just for organic analysis there is a need of fresh RMs, which can be filled by the ESB reference materials.     

Methyl mercury determination in environmental and biological reference and other materials by quality control with certified reference materials (CRMs)

Summary Two concentration methods — HCl extraction and extraction followed by water vapour distillation — prior to anion exchange separation and cold-vapour atomic absorption spectrometry were used for the quantification of methyl mercury in a number of reference materials of biological and environmental origin with reference or certified total mercury contents. The applied methods were validated by the analysis of three marine reference materials, certified for methyl mercury. The results obtained in the materials with methyl mercury contents ranging from less than 1 g/kg to a few hundred g/kg showed good agreement between both methods for biological materials, whereas extraction/anion exchange resulted in somewhat too high values for a number of environmental materials. These findings, however, require further confirmation by additional methods and by other laboratories.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

A pre-irradiation separation procedure based on ion-exchange chromatography for gallium determination in biological and environmental materials by neutron activation analysis

A pre-irradiation separation procedure, for gallium determination in biological and environmental materials by neutron activation analysis (NAA) is reported. The proposed method, based on ion-exchange chromatography, allows to eliminate the radiation risk, while taking the advantages of high sensitivity of NAA. The single comparator method is employed for gallium quantitative evaluation. Since no standard reference materials with certified gallium contents were available, the reliability of the proposed method was extensively investigated by various approaches. Four biological and one environmental standard reference materials, with gallium contents ranging from 54 g/g-3 ng/g, have been analyzed.     

Neutron activation analysis as a tool for checking the reliability of spectrophotometric methods for the determination of molybdenum and tungsten in biological materials

A new method for the simultaneous determination of molybdenum and tungsten in biological materials by neutron activation analysis has been developed. It involves a single step radiochemical separation of both elements by extraction chromatography using -benzoinoxime supported on Bio-Beads SM 2. Good accuracy and precision of the method was demonstrated analyzing Bowen's Kale and IAEA's H-8 /Horse Kidney/ reference materials. The method was applied to check the reliability of the results obtained by one standard and one newly developed spectrophotometric methods for the molybdenum content in some plant materials.     

Determination of cadmium in biological samples by inductively coupled plasma atomic emission spectrometry after extraction with 1,5-bis[phenyl-(2-pyridyl)methylene]-thiocarbonohydrazide

A systematic study was made of the optimum conditions for cadmium determination in biological samples by ICP-AES after extraction of the metal into methyl isobutyl ketone containing 1,5-bis[phenyl-(2-pyridyl)methylene]-thiocarbonohydrazide. The maximum volume ratio of aqueous to organic phase was 30 1 for a single-stage extraction of 99–100% of the metal ion. The detection limit was 0.3 ng/ml cadmium, and the calibration was linear from 0.4 to at least 150 ng/ml. No interferences from the elements commonly found in biological materials were observed. A precision of 2.5% (P = 0.05) at the 2 ng/ml level of the metal was achieved. The accuracy of the method was demonstrated by analysis of three standard reference materials, giving concentrations of 1.90 ± 0.43, 27.1 ± 1.4 and 2.63 ± 0.38 /g of cadmium, compared with the certified values of 2.20 ± 0.10, 26.3 ± 2.1, and 2.71 ± 0.15 g/g, respectively.     

Possibilities of simultaneous determination of lead and thallium in environmental and biological samples by microtron photon activation analysis with radiochemical separation

A method for simultaneous determination of lead and thallium by photon activation analysis with radiochemical separation using irradiation with bremsstrahlung produced by a 20 MeV microtron is described. The detection limits for 500-mg samples of 0.9 g·g^-1 and 0.15 g·g^-1 for lead and thallium, respectively, were achieved that are sufficiently low for the reliable determination of both elements at levels commonly occurring in environmental samples and at elevated levels in biological materials. The accuracy of the procedure developed was proved by analyses of a number of environmental and biological reference materials. Possibilities of detection limit improvements are also discussed.     

An independent accurate reference method for the determination of chromium in biological materials

A method for the determination of Cr in biological materials with high accuracy is reported for use as an independent reference method. It is based on radiochemical neutron activation analysis (RNAA) in combination with an individual yield determination based on the online yield principle. A precision of better than 4% between replicate determinations was achieved by application to biological materials with Cr contents on the 100 g·kg^–1 level. Analytical characteristics of the method offer good perspectives for Cr assays at lower levels.     

The contribution of various analytical techniques to the certification of reference materials

Two international intercomparisons on the determination of trace elements in geological-environmental materials as well as two similar intercomparisons with biological materials provided a large amount of data elucidating the relative significance of various analytical techniques in the process of certification. The data have been investigated concerning their frequency of use, agreement of results by various techniques, percentage of outliers and general performance of the methods. Because many laboratories supplied results for both biological materials and both materials of mineral origin, the analysis of data in the form of two-sample charts has also been presented. The significance of an adequate procedure for outlier rejection for the proper assigning of certified values is emphasized and the unique role of neutron activation analysis in the certification process has been demonstrated. The use of highly reliable (definitive) methods for the verification of recommended values has been demonstrated.     

New Polish certified reference materials for multielement inorganic trace analysis

Summary An overview of the activities of the Polish Institute of Nuclear Chemistry and Technology in the field of preparation and certification of reference materials for multielement trace analysis is presented. A general strategy has been worked out and is briefly described with more detailed emphasis on the problem of data evaluation. Two geological-environmental materials recently issued [i.e. an Apatite Concentrate (CTA-AC-1) and Fine Fly Ash (CTA-FFA-1)] which were certified for 25 and 40 elements, respectively, are described. The preparation and testing of a new CRM of biological origin Oriental Tobacco Leaves (CTA-OTL-1) is presented in detail, including study of the optimum methods for drying, checking homogeneity, radiation sterilization etc. Interlaboratory comparison, in which 61 laboratories participated, yielded results enabling recommended (certified) values for 29 elements and information values for further 11 elements to be established.     

Determination of vanadium in biological matrices by flame atomic absorption spectrometry with activated carbon enrichment

For the determination of vanadium in biological materials by flame AAS an enrichment is described which comprises chelation with oxine and adsorption on activated carbon: The relative standard deviation for 10 g V/L was found to be 6% (n=15).Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Substoichiometric Isotope Dilution Analysis for the Determination of Iron in Biological Materials and Comparison with Substoichiometric Isotope Dilution Mass Spectrometry

Substoichiometric isotope dilution analysis for the determination of trace iron has been studied by using synergistic extraction of iron(III) with a substoichiometric amount of 4-isopropyltropolone (Hipt) in the presence of an excess of 3,5-dichlorophenol (DCP) in heptane. Optimum conditions for the substoichiometric extraction of iron(III) in g to sub-g levels were examined and the high selectivity for iron(III) toward various metal ions encountered in the analysis of biological materials was confirmed. The present method was applied to a biological reference material (NIES, CRM No.9, sargasso) without any pre-separation and was successfully evaluated. Furthermore, substoichiometric stable isotope dilution mass spectrometry using the present extraction method was also used with the above sample. Applicability and practicability was compared for both substoichiometric methods.     

Determination of boron in food and biological reference materials by neutron capture prompt-γ activation

Summary Boron concentrations were determined by in-beam neutron capture prompt- activation analysis for 31 food and biological reference materials prepared by the National Institute of Standards and Technology, Agriculture Canada, the National Institute for Environmental Studies of Japan, and the International Atomic Energy Agency. Sensitivity and background enhancements that are consequences of neutron scattering in hydrogenous matrices such as biological reference materials are discussed, as are correction methods for nuclide interferences, with emphasis on sodium. The limit of quantitation for these materials is 1.0–2.5 g/g and the limit of detection is 0.3–0.8 g/g, depending on the irradiation time. For materials with boron levels 30 g/g (e.g., most botanicals), the total analytical uncertainty is 2%.Temporary summer employment at the United States Food and Drug Administration, 200 C St., SW, Washington, DC 20204, USA     

Determination of Cd,Mo, Cr and Co in biological materials by RNAA

A method for the determination of trace amounts of Mo, Cd, Co and Cr in biological materials by neutron activation analysis with radiochemical separation is presented. The method is based on the ion-exchange scheme developed by SAMSAHL, where Co and Cr are trapped on BioRad Chelex-100 and Cd and Mo on BioRad AG2X8. The elements Mo, Cd and Co can be determined without systematic errors. For the element chromium the situation is less clear, partially due to lack of sufficient certified reference materials for Cr. The method has been used in the characterization of candidate reference materials. Detection limits in these materials range from 1.5 g/kg for Co to 10 g/kg for Cr. Actual levels as low as 8 g/kg for Cd and 7 g/kg for Co were measured.     

The determination of zirconium in biological materials by photon activation analysis

Non-destructive photon activation analysis with 30-MeV bremsstrahlung has been applied for the determination of zirconium in biological materials. The materials investigated were the NBS SRMs Orchard Leaves and Bovine Liver, and various tissues of rats. The detection limits of this method for a 2 h irradiation are 0.1 g for Orchard Leaves, 0.04 g for Bovine Liver and animal tissues. The zirconium contents of animal tissues obtained in this work appear to be significantly lower than the values reported earlier. New data on zirconium in the NBS SRMs are presented.     

Thallium determination in biological materials by radiochemical neutron activation analysis

Summary The determination of thallium in biological materials sometimes cause problems because of the low concentrations of this toxic element. In the present work a method is described which optimizes the parameters affecting the specificity and sensitivity of the radiochemical NAA of thallium in biological samples. High thermal neutron flux, complete decomposition of the organic matter by pressurized digestion, TlI precipitations, liquid extraction of HTlBr₄ and La(OH)₃ scavenging purification are the steps leading to the final homogeneous preparation of Tl₂CrO₄ for -activity measurement. The method was applied to various materials as bovine liver, bone and nails. Good agreement was found between certified and determined thallium concentrations of the reference material CRM 176. The chemical yield comes to about 80%, with low deviations. The sensitivity of the method is about 10^–3 g/g, the standard deviations being in the range of 3.6% (CRM 176), 14% (bovine liver), and 17% (bone). Detailed working instructions are given.     

Determination of mercury in biological materials by CV-AAS after wet digestion

The paper describes the determination of ultratrace concentrations of mercury in biological materials. Samples were digested in nitric acid under pressure in a polytetrafluoroethylene bomb. Mercury was determined in the digest solution by cold vapour atomic absorption spectrometry using stannous chloride reduction and two-stage gold amalgamation. The detection limit is 0.12 ng. Analysis of several certified reference materials yielded results in excellent agreement with the certified values. The results for blood serum of several subjects ranged from 0.2 to 0.8g 1^–1.Of the National Fund for Scientific Research (Belgium), to whom correspondence should be addressed     

Speciation studies for arsenic and mercury-applications and prospects

Methods are described for the speciation of arsenic and mercury in biological and environmental materials. For arsenic various methods were developed to distinguish between more or less toxic arsenic compounds and non-toxic compounds. For the determination of methylmercury a modification of the Westöö procedure was applied for higher contents as well as anion exchange down to levels below 0.1 g/kg in solids and below 0.1 ng/1 in liquids.     

Design,Synthesis, and Application of Stimulus‐Sensing Biohybrid Hydrogels

A key feature of any living system is the ability to sense and react to the environmental stimuli. The biochemical characterization of the underlying biological sensors combined with advances in polymer chemistry has enabled the development of stimulus‐sensitive biohybrid materials that translate most diverse chemical and biological input into a precise change in material properties. In this review article, we first describe synthesis strategies of how biological and chemical polymers can functionally be interconnected. We then provide a comprehensive overview of how the different properties of biological sensor molecules such as competitive target binding and allosteric modulation can be harnessed to develop responsive materials with applications in tissue engineering and drug delivery.

     

A new calibration method for the determination of trace amounts of mercury in air and biological materials

Summary A new calibration method for the determination of mercury by CVAAS using collector preconcentration is described. The main piece of a developed calibration device is a special valve which links a closed Hg — saturated gas flow with an open flow of the carrier gas to the AA — spectrometer. This principle allows the direct injection of defined Hg-saturated gas volumes into the sample gas-flow. In this way the known systematic errors of traditional methods by contamination and loss, caused above all by the manual handling of mercury vapor or solution, are avoided. Instrumental and procedural aspects of the application are discussed and the reliability relating to the mercury determination in air and biological materials is evaluated. The new method is superior to the other calibration methods in every way. In the 1 ng Hg range the within-run precision is better than 1%, and the day-to-day precision better than 2%. The accuracy was validated by determining various biological SRMs. All the results in the g/g and ng/g level corresponded well to certified values. The new method is also a simple and reliable way of carrying out the necessary internal quality control.