Application of displacement reactions in flame photometry-II Emission flame photometric determination of alkaline earth metals in the presence of interfering anions

For the emission flame photometric determination of strontium and barium in the presence of interfering ions such as phosphate, sulphate, arsenate and oxalate, calibration or simple standard addition methods cannot be used. Greatly reduced errors can be achieved by dividing the sample solution into four equal parts and adding to each certain known amounts of two metal ions. One of these is identical to the determinand (e.g., strontium or barium) the other has similar characteristics to it (e.g., calcium). The amounts of these metals are chosen so that the total (molar) concentration of these should be identical in all solutions, but the ratio of the concentrations of the two metals should be different. The emission of the determinand metal must be measured, and a standard addition plot produced. The amount of determinand present in the sample can be obtained from the intersection of the emission vs. concentration line with the concentration axis.     

Substoichiometry in neutron activation analysis technique

Neutron activation analysis has become one of the most sensitive and selective analytical technique for the determination of trace elements in a wide variety of matrices. Neutron activation involves the irradiation of the test sample and a standard of the element to be determined with thermal neutrons in a reactor, followed by dissolution of the test sample in the presence of carrier of the element to be determined. The carrier and radioisotopes are separated from the bulk of other induced activities (employing precipitation, solvent extraction, ion exchange etc.) and then the activity induced in the sample is measured on a suitable detector. The standard is treated identically. From the ratios of the activity of the sample and standard and the weight of the standard irradiated, the concentration of element in the test sample is calculated. A rapid, selective and sensitive method of radiochemical separation is subtoichiometric extraction in which the same amount of carrier is added to the irradiated test sample and standard. Exactly the same amount of reagent is added to both the sample and standard but in substoichiometric amounts, followed by the separation of the species formed by extracting it with an organic solvent. The activities of the extracts are measured. The amount of element present in the sample is calculated with help of the ratio of the activities and the weight of the standard taken. The advantages of the method are discussed. Application of substoichiometry in neutron activation has been elucidated with reference to the determination of Au in various samples by substoichiometric neutron activation analysis.     

Simultaneous determination of iodine and selenium in biological samples by radiochemical neutron activation analysis

Summary Regarding the favourably sensitive nuclear characteristics of iodine and of selenium but the very different half lives of their induced nuclides ¹²⁸I and ⁷⁵Se, a radiochemical neutron activation analysis method for simultaneous determination of these elements in a single sample was developed. It is based on the double irradiation LICSIR technique — Long Irradiation for Se (40h), Cooling (a week or more), Short Irradiation for iodine (1–15 min) with following Radiochemistry. After the second short irradiation, the sample is ignited in an oxygen flask and iodine and selenium are sequentially and selectively extracted as elemental iodine and 5-nitro-2,1,3 benzoselena diazole chelate. With the described method biological samples were analysed and the reliability of the results was checked by the analyses of different standard reference materials. Good agreement with certified values and high radiochemical purity of the spectra show the applicability of the radiochemical separation developed.     

重量法配气的称量数学模型及其不确定度评定

对重量法制备气体标准物质中充入气体质量的计算方法进行了研究,建立了基于单盘电子天平的钢瓶称量方法,并建立了系统的数学模型和不确定度评价方法。为重量法制备气体标准物质提供一种简单、实用和精确的钢瓶称量方法和气体加入质量的计算方法。     

Loss of elements in the oxygen flask decomposition of biological materials: A study by neutron activation analysis

Partial loss of elements in the oxygen flask method for the decomposition of biological materials is described. The irradiated sample is placed in a platinum wire gauze or quartz cup and burnt in an oxygen atmosphere in the presence of carrier solutions. The results obtained by radiochemical neutron activation analysis for the elements like Mn, As, Cu, Sb and Zn in different standard reference materials are presented with a discussion of the possible causes for the lower values.     

Analysis of macro-constituents in steels by PGAA

The determinatin of the concentration of major steel forming elements in 2–5 g steel samples by PGAA and reference to synthetic standard or single comparator is presented. The relative standard deviation is approximately 5%. The analysis time is about 60 min per sample.     

Determination of hafnium and zirconium in geological materials by neutron activation analysis

In this work, neutron activation analysis was applied to analyze the geological standard materials: GSP-1 and W-1 from USGS, GB-1 and BB-1 from the University of Bahia, Brazil and a sample of uraniferous rock. Hf was determined by instrumental method and the obtained results was shown with relative standard deviations varying from 1.1 to 14%. In the case of Zr analyses, both instrumental and radiochemical neutron activation analyses were used. The interference of¹⁵⁴Eu radioisotope that emits -rays too close to those emitted by⁹⁵Zr was eliminated by retention of Zr in an anionic exchange resin column. The contribution of uranium fission product was considered in the Zr determination by using an interference factor. Results of Zr were presented with relative standard deviations varying from 2.0 to 25.7%. More precise results were obtained by using radiochemical separation. The concentration obtained for Hf and Zr in reference materials agreed well with respective certified values or information values.     

Iodine concentration in different human brain parts

Iodine is one of the most important essential elements as demonstrated by the fact that its deficiency can cause goitre. Nevertheless, quantitative data on its concentration in biological materials, especially in the human brain, are scarce. There is therefore a demand for accurate and reliable information on iodine in these types of samples. The purpose of the present work was to determine the concentration of total iodine in some control human brain parts by rapid radiochemical neutron activation analysis. Our second goal was to determine I distribution between lipid fraction and in brain tissue without lipid by applying two types of solvent extraction methods. The results were checked by the analysis of biological standard reference materials with certified or literature values for iodine and good agreement was found.     

Determination of radiocesium in environmental water samples using copper ferro(II)cyanide and sodium tetraphenylborate

Summary A procedure for the radiochemical separation and radiochemical purification of radiocesium (¹³⁴Cs and ¹³⁷Cs) in bulk environmental water samples is proposed. Radiocesium was removed from the water by cation-exchange with copper ferro(II)cyanide and was purified by precipitation with sodium tetraphenylborate. The influence of the concentration of potassium in the water sample on the chemical yield was investigated. The validation of the proposed method was carried out by analyzing reference materials. The application of the method was demonstrated with the determination of the concentration of radiocesium in water samples from rivers around NPP “Kozloduy”, Bulgaria, Danube and Ogosta.     

XRF induced by PIXE: Comparison with PIXE

Two different modes of sample excitation have been used for elemental analysis of thin standard reference materials and of chemical standards with known composition. PIXE /2.5 MeV protons/ and XRF induced by PIXE, will be called XRF-PIXE /2.5 MeV protons on Mo primary target/. The same samples were alternatively exposed to protons and X-ray beams. The sensitivities under standard running conditions are determined for both an XRF-PIXE and a PIXE analysis system. It is shown that the sensitivity of the PIXE spectrometer depends strongly on the sample matrix, whereas the XRF-PIXE sensitivity is rather constant with respect to different kinds of samples. In addition, the advantages of one mode of excitation on the other are discussed. It is shown that XRF-PIXE can be a useful complement to PIXE analysis.     

A comparison of the external standard and standard addition methods for the quantitative chromatographic determination of pesticide concentrations in plant samples

Model samples containing known amounts of pesticides in various plant materials were analyzed, and the accuracies of the external standard and standard addition methods were compared based on a criterion such as the relative analyte concentration. It was found that traditionally recommended procedures for the solvent extraction of pesticides from samples of this kind in combination with quantitative analysis by the external standard method determine only 10–70% of the true concentrations of analytes. This is most likely due to analyte adsorption on matrices and/or incomplete extraction. In almost all cases, the use of the standard addition method compensates pesticide losses at the stages of sample preparation and thereby considerably decreases the systematic error of determination. The extrapolation of analyte concentration to the zero amount of the added reference sample was proposed to additionally control the accuracy of results obtained by the standard addition method. Moreover, it was found that solid-phase extraction as the second stage of sample preparation has no considerable advantages over back solvent extraction in terms of the above criterion. This is because the main analyte losses were observed at the first stage of extraction from test samples.     

Radiochemical neutron activation analysis of traces of vanadium in biological samples: A comparison of prior dry ashing with post-irradiation wet ashing

Summary A radiochemical neutron activation technique for nanogram and subnanogram levels of vanadium in biological samples was developed, based on dry ashing of the sample prior to irradiation, but without any chemical treatment. It was compared to and validated by parallel analyses of low-level reference materials and human blood using a previously developed totally post-irradiation technique based on rapid wet ashing of the irradiated sample. The irradiated ash was also wet ashed after neutron bombardment to ensure complete dissolution, equilibration with carrier and removal of ³⁸Cl. Results for reference materials, including Versieck's Second Generation Human Serum Reference Material and IAEA Animal Blood, were in excellent agreement by the two techniques, and with reference to literature values. Both methods give exceptionally good radiochemical decontamination of ⁵²V from other nuclides and have nearly quantitative yields. The dry ash mode is slightly quicker and easier to manipulate.     

The elimination of matrix effects in the determination of fluorine by proton induced prompt gamma-spectrometry

By measuring the yield of prompt gamma-rays, induced by energetic protons, the ratio of the ranges in sample and standard was used in the average cross-section method to determine fluorine. By spiking the sample with known amounts of a lithium compound, a nonanalyte element (absent from the sample), the appropriate ranges in the samples were determined by measuring the prompt gamma-rays induced in the non-analyte spike. Fluorine was determined in ores and ivory and the method was tested by analyzing the standard reference materials SRM 91, SRM 120c and SRM 694.     

Neutron activation analysis of scandium

A neutron activation method is proposed for the determination of trace quantities of scandium, down to submicrogram level, in rocks, ores and meteorites. The sample and standard are irradiated intermittently for a total of 30 h, at a neutron flux of 5·10¹¹ n/cm²/sec; the radiochemical separation consists essentially of a one-step anion exchange. The induced γ-activity of ⁴⁰Sc, 85 days, isolated from the sample is measured and compared with that of a standard. The chemical yield averages 85% and there is a considerable saving of time in the radiochemical work. Results are quoted for the scandium contents of 2 standard rocks, cassiterite and several stony meteorites. Details of conflicting nuclear reactions are also given.     

Highly accurate radiochemical neutron activation analysis of arsenic in biological materials involving selective isolation of arsenic by hybrid and conventional ion exchange

A highly accurate (definitive) radiochemical neutron activation analysis (RNAA) method was developed for the determination of traces of arsenic (As) in biological materials. It consists of the following steps: (a) irradiation in the nuclear reactor; (b) microwave-assisted sample digestion; (c) quantitative and selective radiochemical separation of arsenates on hydrated ferric oxide nanoparticles dispersed in a macroporous cation exchanger, preceded by a conventional strongly acidic cation exchanger column, and (d) gamma-ray spectrometric measurement of ⁷⁶As. The suitability and accuracy of the method was demonstrated by analysing several certified reference materials. The detection limit is 8 ng g^?1. The standard uncertainty in the determination of As in oriental tobacco leaves is around 3.4%. This, together with its compliance with several other formal requirements, makes the method comparable to primary methods based on isotope dilution mass spectrometry.     

Study on the comparator method using substoichiometry

The comparator method using substoichiometry is developed. In the method, the contents of the elements can be determined simultaneously by the measurement of radioactivities of the comparator elements and of simultaneously separated parts of the elements in question. The method is applied to the simultaneous determination of rare earth elements, such as lanthanum, europium and terbium in NBS botanical standard reference materials. It is confirmed that the method is reliable for simultaneous multielement determination.     

Determination of iodine in human brain by epithermal and radiochemical neutron activation analysis

Despite the role of iodine for proper development of the brain and the functions of the element, the accurate data on its concentration in brain tissue are largely lacking, the main reason being analytical difficulties associated with determination of the element especially at low levels. In this work, samples from human brain regions from Hungarian patients were analyzed using epithermal and radiochemical neutron activation analysis (ENAA and RNAA, respectively). The RNAA procedure is based on alkaline-oxidative fusion followed by extraction of elemental iodine in chloroform. The results were checked by the analysis of biological standard reference materials, namely bovine liver, bone meal and diet, and by comparison with previous results obtained by a different RNAA procedure.     

Study on the comparator method using substoichiometry I. Principle

A new comparator method using substoichiometry was developed. In this method, the content of the element can be determined by the measurement of both radioactivities of an isolated part of the element in question and of the comparator. The method was applied to the determination of lanthanum in NBS botanical standard reference materials, and availability of the method was shown.     

XRF检验标准物质中痕量元素的匀性

本文讨论了用Ｘ射线荧光光谱检验标准物质中痕量元素的均匀性时，可根据峰和背景强度确定能否用ＸＲＦ进行检验，以及相应于一定精度度要求的浓度下限（可检浓度），并以大米和岩石标准物质为例，计算了Ｃ－的可检浓度。还指出，作为均匀性检验量应采用浓度或净强度，尤其是对于痕量元素，最后说明了样品基体对可检浓度和最小样品量的影响。     

Average stopping powers and the use of non-analyte spiking for the determination of phosphorus and sodium by PIPPS

Using particle induced prompt photon spectrometry, PIPPS, the ratos of the average stopping powers in samples and standards can be used to determine elemental compositions. Spiking the sample with a known amount of a non-analyte (lithium) compound with known stopping power, appropriate stopping powers in the samples can be determined by measuring the prompt gamma-ray yields induced in the spike. Using 5 MeV protons sodium and phosphorus were determined in ivory, while sodium was determined in geological samples. The method was tested by analyzing the standard reference materials SRM 91, 120c and 694.