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Abstract  

A rapid and sensitive spectrophotometric method has been developed for the determination of thorium using 0.04% Arsenazo-III in a 2M perchloric acid solution. Absorbance was measured in 1 cm cell and the complex has a sensitive absorption peak at 654 nm. The complex is formed instantly in perchloric acid and remains stable for 45 minutes with constant absorbance. Beer's law is obeyed in the range 1–60 g·g–1 of thorium concentration with a molar absorptivity at 654 nm = 3.07·105 M–1·cm–1 at 24±2°C. The foreign ions interference in thorium determination have been checked. The cations were tested at >60-fold excess of thorium, Mn(II), Fe(III), Co(II) and Ni(II) interfere negatively, whereas only Ce(III) has increased the absorbance. Among the anions, cyanide, phosphate, thiocyanate and acetate at 150-fold excess of thorium cause significant interference. However, thorium can bedetermined in the presence of nitrate, chloride, oxalate, tartrate, ascorbate, thiosulphate and citrate. The method has been applied on certified reference material for thorium determination after extractive separation and the result was found in good agreement with the certified value. The method has been also applied successfully to determine thorium at g·g–1 level in local ore samples with a precision of ±0.04%.

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Abstract  

A rapid analytical method of Pu in environmental samples by alpha-ray spectrometry and high-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) using a 3M Empore anion exchange resin disk for solid phase extraction has been developed. A trace amount of Pu was quantitatively adsorbed with an Empore anion exchange resin disk (47 mm diam.) at a flow rate of 150–200 ml/min from 8M HNO3 sample solution. The disk was washed with 10 ml of 8M HNO3 and 12 ml of 9M HCl and then the Pu was quantitatively eluted with 15 ml of 1M HNO3/0.03M ascorbic acid solution. The time needed to separate Pu from the sample solution with the present method was about 20 minutes. The separated Pu was determined with alpha-ray spectrometry and HR-ICP-MS. The present method was applied to the determination of Pu in the certified reference material (IAEA-135) and the environmental soil sample. The analytical results were almost in good agreement with the literature values.

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Abstract  

Performance characteristics (especially accuracy) of a routine INAA with k0 standardization were verified and compared with those of INAA with a classical single comparator. For this purpose, samples of three certified reference materials of environmental origin (Fly Ash, Orchard Leaves and Buffalo River Sediment—all supplied by NIST) were irradiated with both kinds of comparators (Au–Zr for k0 and Zn for classical k method) in one irradiation rabbit. Also the following steps of INAA procedure were practically the same for both standardization methods used (counting, spectral processing, etc.). The results have shown that the k0 method gives sufficiently accurate results comparable with those of the well established and routinely used single comparator (Zn) method, provided proper neutron flux monitoring, efficiency calibration and also coincidence summing corrections are applied. This work shows that modern k0 standardization method in INAA can be sucessfully used in routine practice and applied with an advantage in INAA laboratories subject to changes of neutron spectra or counting conditions.

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Abstract  

Characterizations of three major parameters of Certified Reference Materials (CRMs) concentration values of multielements, homogeneities of multielements, and stabilities of the materials, were further studied by NAA. In the determinations of multielements in RMs, both relative and K0 (and its extension) standardizations were used in an effort to detect hidden systematic errors and expand the number of determinable elements. In the evaluations of multielemental homogeneities, double sampling constants as well as Ingamells' Ks and F-test were used to establish semi-quantitative expressions of sampling uncertainty vs. size and number of subsamples for given elements in given materials. For the investigation of the stabilities of certified values, K0 NAA is to be used in follow-up analyses to test variations of certified values and provide updated and/or newly determined data. The final goal is to make NAA a definitive method for multi-trace element certification, a reliable method for homogeneity characterization, and a reproducible method for stability test. Examples are given to show preliminary results on the above aspects.

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Abstract  

The intake of leafy vegetables in daily diet is very important to meet our nutritional needs. Vegetables provide the essential elements which are necessary and recommended for human growth. However, due to rapid industrialization and urbanization our environment becomes polluted and this affects the normal growth of agricultural products and composition of environmental species. The elemental concentrations present in the environmental samples are good indicators to assess the toxicological levels due to pollution affects. In the present work we have analysed several vegetable plant samples by instrumental neutron activation analysis to determine the elemental concentrations at major, minor and trace levels. The leafy vegetables like spinach, red leafy veagetable, pui, gourd leaf, lettuce and katoua were chosen as these are extensively consumed by local peple in eastern part of India. We have determined 15 elements in the above mentioned vegetable samples and some of these are essential elements and some are toxic elements. It was found that Na and K were present as major elements, Fe and Zn as minor elements and As, Ce, Cr, Co, La, Mo, Rb, Sc, Sm, Sr as trace elements. The concentration level of Cr was found to be higher than that of recommended value certified by WHO and National environment quality control for human consumption. The validation of our analytical results have been performed by the Z-score tests through the determination of concentrations of the elements of interest in certified reference materials.

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Abstract  

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.

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Abstract  

The Portuguese Research Reactor (RPI) is a 1 MW swimming pool type reactor, operating since the early 1960s. The fuel is MTR type, with flat plates of U-Al alloy enriched to 93% in 235U. As the core configuration changed in April 2000, it became essential to characterise the neutron field in the most useful irradiation positions of RPI, in order to guarantee the accuracy in the application of k 0-neutron activation analysis (k 0-NAA). Experimental values of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from the 1/E shape (a) were determined using the Cd-ratio for multi-monitor method. The neutron temperature (T n) was obtained from co-irradiation of Lu with 1/v monitors. The results for several irradiation positions are presented and discussed in this work. Some element concentrations are determined based on the parameters obtained in this work, and compared with the certified reference material concentrations.

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Summary  

137Cs and to a lesser extent, 210Pb have been widely used for soil erosion and sedimentation studies. The accuracy of their quantification is greatly dependent on the proper handling of the sources of error that may affect the results. These include ambient background variation, attenuation for the 210Pb 45 keV gamma-photons in the sample, efficiency calibration and large statistical errors due to low levels of radioactivities and small sample quantities combined with Compton scattering of high energy photons during acquisition. In this study, we investigated the distribution of both 210Pb and 137Cs in three soil cores from Konza and Fort Riley, Kansas. Special attention was given to the analytical treatment of the spectra and the uncertainty budget. We show here that the ambient background is a major factor in the results. If it is not well monitored, errors of as high as 25& can result. We investigated the advantages of using Compton suppression with gamma-ray spectrometry for 137Cs and 210Pb quantification. Natural matrix certified reference materials (CRM) were used for efficiency calibration and quality assurance.

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Abstract  

The characterized concentrations of 24 impurity elements in New Brunswick Laboratory (NBL) Certified Reference Material (CRM) 124 were reevaluated. A provisional certificate of analysis was issued in September 1983 based upon the “as prepared” values (gravimetric mixing). The provisional certificate does not state uncertainties for the characterized values, or estimate the degree of homogeneity. Since release of the provisional certificate of analysis various laboratories have reported analytical results for CRM 124. Based upon the reported data a re-evaluation of the characterized values with an estimate of their uncertainties was performed in this work. An assessment of the degree of homogeneity was included. The overall difference between the re-evaluated values for the 24 impurity elements and the “as prepared” values from the provisional certificate of analysis is negligible compared to the uncertainties. Therefore, NBL will establish the “as prepared” values as the certified values and use the derived uncertainties from this work for the uncertainties of the certified values. The traceability of the “as prepared” values was established by the gravimetric mixing procedure employed during the preparation of the CRM. NBL further recommends a minimum sample size of 1 g of the CRM material to ensure homogeneity. Samples should be dried by heating up to 110 °C for one hour before use.

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The aim of this study was the comparison of different sample preparation methods for multielemental ICP-MS analysis of wine samples. All investigated methods were previously published for the same purpose, but the comprehensive comparison was carried out in the frame of this study for the first time. Five wine samples of different residual sugar content (2 dry, 2 sweet and one extra fine quality dessert wine) were used from Hungarian wine districts. Due to the lack of certified reference materials method validation and cross-checking was carried out by using two different types of inductively coupled plasma mass spectrometers (ICP-MS), namely a quadrupole based ICP-MS equipped with a collision cell (ICP-CC-MS) and a high resolution sector field ICP-MS (ICP-SF-MS). The measured elements were Li, Mg, B, Al, Cu, Rb, Sr, Zr, Cd, Ba, Tl, Pb, Bi, U, Cr, Fe, Mn, Co, Ni, Zn, As, Mo and Ga.Sample preparation procedures were based on sample dilution, microwave digestion using nitric acid (in combination with and without evaporation prior to ICP-MS analysis) and a mixture of nitric acid and hydrogen peroxide. The investigation resulted that the optimal digestion method for the above-mentioned purpose is microwave digestion using nitric acid without evaporation. The advantages and disadvantages of the investigated methods are critically discussed.

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