Further study on parametric standardization in reactor NAA

A post-K_o study of parametric reactor NAA is described including the determination and applications of working K_oS for non-1/V reactions¹⁵¹Eu(n,)¹⁵²Eu and¹⁷⁶Lu(n,)¹⁷⁷Lu; parametric corrections for²³⁵U fission, threshold reaction and -spectral interferences; and parametric normalizations for different counting geometries. The analytical significance, the principles, the experimental confirmations, and the application examples of these methods are briefly introduced.     

Determination of chromium in biological reference materials by instrumental NAA using Compton suppression

Instrumental neutron activation analysis in conjunction with Compton suppression methods has been used to determine chromium concentrations in 13 biological reference materials. Special attention was focussed on the interferences and the ways of lowering their contribution. Separate data was obtained for normal and Compton suppressed modes of counting so that a comparison could be performed. The results for chromium as compared to the certified or compilation values were in excellent agreement.     

Comparison of NAA methods to determine medium-lived radionuclides in NIST soil standard reference materials

In order to determine the elemental concentrations of three new soil standard reference materials SRMs 2709, 2710 and 2711 from the National Institute of Standards and Technology (NIST), a comparative study of different medium-lived neutron activation analysis methods was carefully performed. Three irradiation conditions (1-hour thermal, 1-hour epithermal and 5-minute epithermal) and two counting modes (normal and Compton suppression) have been evaluated for following ten elements: As, Au, Cd, Ga, K, La, Mo, Sb, Sm, and W. The results show that the method of 5-minute epithermal and a 1-day decay is the optimum way to analyze Ga, while the addition of the Compton suppression is very beneficial for the determination of K. Using the Compton suppression system in conjunction with the 1-hour epithermal and a 1-week decay, is ideal to determine Au, Cd, Mo and W, while routine 1-hour thermal and a 1-week decay, is adequate to determine As, Sb, Sm and La in concentrations found in soil.     

Selenium determination in biological materials by NAA

Results for Se in several biological standard reference materials obtained by INAA and selective RNAA procedures developed in our laboratory, are presented and discussed. The comparison of selenium levels in selected blood plasma samples determined by non-destructive NAA and HG-AAS is also presented. The reproducibility and accuracy of the analytical procedure was tested and the results of these investigations were compared with the certified values.     

Thermal behavior study of biodiesel standard reference materials

Quality control of fuel-related properties of biodiesel, such as thermal stability, is needed to obtain consistent engine performance by fuel users, since biodiesel is susceptible to auto-oxidation when exposed to air, light, and temperature during storage. In this work two pure standard reference materials of biodiesels produced from soy oil and animal feedstocks were studied. Differential scanning calorimetry and thermogravimetry measurements were performed and the analysis of the results revealed small temperature variations in the thermal events among the two standards, these differences are due mainly to their chemical composition, been highly influenced by the amounts of unsaturated esters.     

Determination of silver in SOIL-7 standard reference material by NAA

IAEA standard reference material SOIL-7 has been analyzed by both instrumental NAA and radiochemical NAA using epithermal neutron activation. These analyses confirm the NAA value of Ag in the intercomparison SOIL-7 which disagrees with some AAS values. Further geostandards were included and compared with literature data.     

The validation of Kayzero-assisted NAA in Budapest, Rez, and Ljubljana via the analysis of three BCR certified reference materials

After installation and calibration of k0-assisted NAA in three Central European research institutes (AEKI-Budapest, NPI-Rez, and IJS, Ljubljana), its validation was established via the analysis of three BCR certified reference materials. The matrices of choice were: CRM 277 estuarine sediment, CRM 038 coal fly ash from pulverized coal, and CRM 101 spruce needles. For some elements, e.g. Zn, Cd, and Hg, the analyses were not only performed instrumentally (INAA), but also in the radiochemical mode (RNAA). The work was performed in the framework of a European Copernicus Project.     

New definitions on reference materials

The new definitions for reference material and certified reference material as approved by ISO REMCO are provided and further explained.     

The validation of Kayzero-assisted NAA in Budapest, Řež, and Ljubljana via the analysis of three BCR certified reference materials

After installation and calibration of k₀-assisted NAA in three Central European research institutes (AEKI-Budapest, NPI-?e?, and IJS, Ljubljana), its validation was established via the analysis of three BCR certified reference materials. The matrices of choice were: CRM 277 estuarine sediment, CRM 038 coal fly ash from pulverized coal, and CRM 101 spruce needles. For some elements, e.g. Zn, Cd, and Hg, the analyses were not only performed instrumentally (INAA), but also in the radiochemical mode (RNAA). The work was performed in the framework of a European Copernicus Project.     

Review of neutron activation analysis in the standardization and study of reference materials, including its application to radionuclide reference materials

Summary Neutron activation analysis (NAA) plays a very important role in the certification of reference materials (RMs) and their characterization, including homogeneity testing. The features of the method are briefly reviewed, particularly aspects relating to its completely independent nuclear basis, its virtual freedom from blank problems, and its capacity for self-verification. This last aspect, arising from the essentially isotopic character of NAA, can be exploited by using different nuclear reactions and induced nuclides, and the possibility of employing two modes, one instrumental (nondestructive), the other radiochemical (destructive). This enables the derivation of essentially independent analytical information and the unique capacity of NAA for self-validation. The application of NAA to quantify natural or man-made radionuclides such as uranium, thorium, ²³⁷Np, ¹²⁹I and ²³⁰Th is discussed, including its advantages over conventional radiometric methods, and its usefulness in providing independent data for nuclides where other confirmatory analyses are impossible, or are only recently becoming available through newer atom counting techniques. Certain additional, prospective uses of NAA in the study of RMs and potential RMs are mentioned, including transmutation reactions, creation of endogenously radiolabelled matrices for production and study of RMs (such as dissolution and leaching tests, use as incorporated radiotracers for chemical recovery correction), and the possibility of molecular activation analysis for speciation.     

Computer-assisted reactor NAA of geological and other reference materials,using the k0-standardization method: Evaluation of the accuracy

A scheme for instrumental neutron activation analysis of ancient and medieval glasses is proposed. The combination of three irradiations (short time, pile and epithermal) enables the determination of 34 elements. The accuracy of the method is evaluated by analyzing two glass standard reference materials. Results from the analysis of three glasses from different times are presented.     

Advances in in-situ characterizations of electrode materials for better supercapacitors

In past decades,the performance of supercapacitors has been greatly improved by rationalizing the electrode materials at the nanoscale.However,there is still a lack of understanding on how the charges are efficiently stored in the electrodes or transported across the electrolyte/electrode interface.As it is very challenging to investigate the ion-involved physical and chemical processes with single experiment or computation,combining advanced analytic techniques with electrochemical measurements,i.e.,developing in-situ characterizations,have shown considerable prospect for the better understanding of behaviors of ions in electrodes for supercapacitors.Herein,we briefly review several typical in-situ techniques and the mechanisms these techniques reveal in charge storage mechanisms specifically in supercapacitors.Possible strategies for designing better electrode materials are also discussed.     

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.     

Stability of reference materials

Summary The problem of stability of reference materials is particularly difficult when dealing with complex biological matrices and certification of the content of relatively unstable organic components. This paper considers two aspects of the problem: a) the preparation and packaging of material in a form which gives the greatest likelihood of achieving acceptable stability; b) the design of the measurement studies undertaken to monitor short-term stability for shipment, laboratory handling and long-term storage stability.     

Availability of reference materials: COMAR the database for certified reference materials

COMAR is the international database for certified reference materials. A new user-friendly web-based version, COMAR², has been developed by BAM and CONET Consulting AG which will be available in December 2002. The advantages of COMAR² are briefly explained.Presented at the International ILAC/IAF Conference on Accreditation in Global Trade, 23-25 September 2002, Berlin, Germany     

The study of the stability of reference materials by isochronous measurements

An alternative method for stability testing of candidate certified reference materials (CRMs) utilizing “isochronous” measurements based on a storage design (storing samples at different temperatures for different time periods), which allows all measurements to be done at the same time, i.e. at the end of the study, is compared to “classical” designs of stability studies using reference time or reference temperature. The execution of stability studies using “isochronous” measurements only requires repeatability conditions, whereas classical designs require both repeatability and long term reproducibility conditions. Consequently, the new design allows the quality of results to be improved.     

Extending NAA to materials with high concentrations of neutron absorbing elements

Summary The recently discovered universal functions for thermal and epithermal neutron self-shielding were adapted to NAA of cylindrical samples, expressing the magnitude as the product of a nuclear factor, a geometrical factor and the amount of the neutron absorbing element. The theory was tested and the nuclear factors were measured for 1 ml samples containing the halogens Cl, Br and I. Tests on samples containing these elements at a priori unknown concentrations, irradiated in a mixed thermal and epithermal neutron spectrum, showed that self-shielding as high as 30% could be corrected with an accuracy of about 1%, except in cases with significant epithermal shielding of one element by another.