It is generally accepted that an analytical procedure can be regarded as an information production system yielding information on the composition of the analyzed sample. Thus, information theory can be useful and the quantities characterizing the information properties of an analytical method may be applied not only as evaluation criteria but also as objective functions in the optimization. The usability of information theory is demonstrated on the example of neutron activation analysis. Both precision and bias of NAA results are taken into account together with the possible use of reference materials for quality assessment. The influence of the above-mentioned parameters on information properties such as information gain and profitability of NAA results is discussed in detail. It has been proved that information theory is especially useful in choosing suitable reference materials for the quality assessment of routine analytical procedures not only with respect to matrix and analyte concentration in the sample but also to concentrations and uncertainties of certified values in the CRM used. In the extreme trace analysis, CRMs with relatively large uncertainties and very low certified concentrations can still yield rather high information gain of results.
Authors:R. Rao, L. McDowell, C. Jayawickreme, and A. Chatt
The homogeneity of four reference materials was evaluated for Se by cyclic instrumental neutron activation analysis (CINAA). The relative standard deviation for Se measurements at ppb levels by CINAA was <12% for NIST Wheat Flour (SRM 1567) in 5–10 mg samples, while it was <11% for Chinese Hair (HH–CH-1), <13% for IAEA Animal Muscle (H-4) and 25% for IAEA Animal Blood (A-13) in 50 mg samples. The highest relative subsampling uncertainties were observed in the mass range of samples 50 mg for Chinese Hair, 100 mg for Wheat Flour and Animal Muscle and 300 mg for Animal Blood. The results of a one-way analysis of variance indicate that all reference materials above these mass ranges are adequately homogeneous with respect to Se distribution. Our data suggest that these materials, except Animal Blood, can be used as reference standards for Se in Quality assurance programs well below the sample masses re commended by the issuing agencies.
Authors:R. Dybczyński, B. Danko, and H. Polkowska-Montrenko
Homogeneity of the existing (Virginia Tobacco Leaves CTA-VTL-2 (ICHTJ), Apatite Concentrate CTA-AC-1 (ICHTJ), Fine Fly Ash CTA-FFA-1 (ICHTJ) and candidate certified reference materials (CRMs) (IAEA-338 Lichen, IAEA-413 Algae, Spruce Shoots RMF II (Germany)) was studied by neutron activation analysis (NAA). Several samples of small mass (ca. 1 or 10 mg) taken from various containers were analyzed by instrumental NAA and the results for several elements were compared by Fisher's test and t-test with analogous series of results for samples taken from one container. In the second approach, sampling variance was estimated for some elements from overall variance and the components of analytical variance. The results were interpreted with the aid of Ingamells' sampling constant. Particle size distribution of the reference materials was also measured by several techniques. In addition quantitative determinations for some elements were performed and results compared with the certified values. The results of the present study were discussed with reference to suitability of CRMs to microanalytical techniques. It was pointed out that the term "microanalysis" itself is not always unequivocally understood and used.
A new type of synthetic multi-element reference material (SyRM) with pseudo-biological matrix was prepared by a co-polymerization
reaction of an aqueous solution of acrylamide and acrylic acid containing known amounts of the elements. SyRM has the excellent
homogeneity and the quantitative retention of major and trace elements. Elemental composition can simulate the biological
samples to be analyzed. SyRM can be used for the same purpose of conventional certified reference materials with high accuracy
and precision. SyRM was applied as a comparative standard for non-destructive photon and α-particle activation analysis. Selective
preconcentration methods combined with NAA were proposed and the SyRM containing about fifty elements with known amounts was
prepared. In order to evaluate the reliability of present methods, 3d transition elements and rare earth elements were determined
in the SyRM. It was clearly observed that these methods have good accuracy and precision in trace analysis of biological materials
by comparing the analytical results with the original contents in the SyRM. The SyRM supported multielement analysis of marine
macro-algae can be used as comparative standards for the quality assurance of analytical techniques.
Ten selected rock reference materials (USGS diabase W-1, basalt BCR-1, andesite AGV-1, granite G-2, granodiorite GSP-1, and
CRPG basalt BE-N, granite GS-N, trachyte ISH-G, serpentine UB-N, glass standard VS-N) were analyzed by instrumental neutron
and photon activation analyses. The results have been evaluated on average for the entire set of samples to detect possible
systematic deviations of the determined values from the reference values. Out of 47 elements determined, 43 elements have
been determined with reasonable agreement (deviation < 10% on average) with the reference values. Au could not be determined
because of a high blank from packaging polyethylene foil. Systematically higher Dy and lower Ho and Tm (by about 20% on average)
in the present results require further investigation. In several cases, reasons for greater differences between the determined
and recommended values could not be traced in the procedures used within the study. The most suspect is the recommended value
for W in the CRPG BE-N basalt, which is twenty-five times higher than the present value, probably due to inconsistent contamination
from a W carbide mill used in production of this reference material.
Twelve biological-matrix, agricultural/food reference materials, Corn Stalk (Zea Mays) (NIST RM 8412), Corn Kernel (Zea Mays) (NIST RM 8413), Bovine Musele Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415), Microcrystalline Cellulose (NIST RM 8416), Wheat Gluten (NIST RM 8418), Corn Starch (NIST RM 8432), Corn Bran (NIST RM 8433), Whole Milk Powder (NIST RM 8435), Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437) and Soft Winter Wheat Flour (NIST RM 8438) were developed. They were characterized with respect to elemental composition via two extensive international interlaboratory characterization campaigns providing 303 reference and informational concentration values for 34 elements (Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Ti, V, W, Zn) of nutritional, toxicological, and environmental significance. These products are available to the analytical community, for quality control of elemental composition analytical data, from the Standard Reference Materials Program, National Institute of Standards and Technology, Gaithersburg, MD, USA.
Multielement determination in reference materials of diet and its relatedsamples has been studied by a k 0 based neutron-induced prompt gamma-ray analysis(PGA) by using cold and thermal guided neutron beams of JRR-3M at JAERI. Hydrogen,B, C, N, Na, S, Cl, K and Ca were determined in the reference materials ofNIES and NIST typical diet and milk powder samples. Analytical results ofthe NIST Standard Reference Materials agreed with the certified values towithin 7%.
Authors:K. Inn, Zhichao Lin, Zhongyu Wu, C. McMahon, J. Filliben, P. Krey, M. Feiner, Chung-King Liu, R. Holloway, J. Harvey, I. Larsen, T. Beasley, C. Huh, S. Morton, D. McCurdy, P. Germain, J. Handl, M. Yamamoto, B. Warren, T. Bates, A. Holms, B. Harvey, D. Popplewell, M. Woods, S. Jerome, K. Odell, P. Young, and I. Croudace
In 1977, the Low-level Working Group of the International Committee on Radionuclide Metrology met in Boston, MA (USA) to define the characteristics of a new set of environmental radioactivity reference materials. These reference materials were to provide the radiochemist with the same analytical challenges faced when assaying environmental samples. It was decided that radionuclide bearing natural materials should be collected from sites where there had been sufficient time for natural processes to redistribute the various chemically different species of the radionuclides. Over the succeeding years, the National Institute of Standards and Technology (NIST), in cooperation with other highly experienced laboratories, certified and issued a number of these as low-level radioactivity Standard Reference Materials (SRMs) for fission and activation product and actinide concentrations. The experience of certifying these SRMs has given NIST the opportunity to compare radioanalytical methods and learn of their limitations. NIST convened an international workshop in 1994 to define the natural-matrix radionuclide SRM needs for ocean studies. The highest priorities proposed at the workshop were for sediment, shellfish, seaweed, fish flesh and water matrix SRMs certified for mBq per sample concentrations of 90 Sr, 137 Cs and 239 Pu + 240 Pu. The most recent low-level environmental radionuclide SRM issued by NIST, Ocean Sediment (SRM 4357) has certified and uncertified values for the following 22 radionuclides: 40 K, 90 Sr, 129 I, 137 Cs, 155 Eu, 210 Pb, 210 Po, 212 Pb, 214 Bi, 226 Ra, 228 Ra, 228 Th, 230 Th, 232 Th, 234 U, 235 U, 237 Np, 238 U, 238 Pu, 239 Pu + 240 Pu, and 241 Am. The uncertainties for a number of the certified radionuclides are non-symmetrical and relatively large because of the non-normal distribution of reported values. NIST is continuing its efforts to provide the ocean studies community with additional natural matrix radionuclide SRMs. The freeze-dried shellfish flesh matrix has been prepared and recently sent to participating laboratories for analysis and we anticipate receiving radioanalytical results in 2000. The research and development work at NIST produce well characterized SRMs that provide the world's environment-studies community with an important foundation component for radionuclide metrology.
Thirty four elements (Al, As, Ba, Br, Ca, Ce, Co, Cr, Cs, Dy, Eu, Fe, Gd, Hf, Ho, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sb, Sc, Sm, Ta, Tb, Th, Ti, U, V, W, Yb) were determined by instrumental neutron activation analysis in the second set of Chinese geochemical standard reference materials (sediments from GSD-9 to GSD-12, soils from GSS-1 to GSS-8, rocks from GSR-1 to GSR-6) using both thermal and epithermal irradiations. Irradiation schemes designed to utilise short, medium and long-lived nuclides were employed in order to analyse major, minor and trace elements with different half-lives. The gamma-ray spectra were measured by Ge(Li) and HP(Ge) detectors. Relevant nuclear data and possible interferences are listed, and analytical results are presented and discussed.
Individual samples of several sets of plants (lichens, tobacco, spruce needles, grass, botanical reference materials) show highly significant correlations of Al, Fe, Hf, La, Na, Th, Ti and V with Sc. These correlations result from the terrigenous part of aerosols deposited on and measured together with the plants. The composition of this contamination is almost uniform among the different plant sets and can be approximated by the composition of the upper continental crust. The mass of the terrigenous material ranges from <1 to >100 mg/g plant. Its presence is expected to lead to concentrations of the above and of other elements that deviate substantially from those of plants without contamination. This is proved by the comparison of two sets of spruce needles, one of which was measured without and the other after removal of the aerosol.