Redox substoichiometric determination of arsenic in biological materials by neutron activation analysis

A redox substoichiometry is proposed for an accurate and precise determination of arsenic. This method is based on the substoichiometric oxidation of trivalent arsenic to pentavalent with potassium bromate or ceric sulfate followed by the separation of these species by thionalide extraction of trivalent arsenic. It was applied to neutron activation analysis of arsenic in the NBS SRM Orchard Leaves and the Shark Powder. The results were obtained with an excellent accuracy and precision.     

Determination of iodine in biological materials by neutron activation analysis

A method of determination of iodine (total and PBI) in serum, urine and other biological materials has been developed. The method consists in a gamma-spectrometric measurement of¹²⁸I activity after its radiochemical separation. The radiochemical separation procedure includes wet decomposition of the samples in a nitric acid medium followed by a few separation steps, the essential step being the substoichiometric extraction of iodide with a chloroform solution of tetraphenylarsonium chloride. Owing to the application of the substoichiometric separation, a high radiochemical purity of the separated iodine is achieved and the determination of the yield of radiochemical separation is not necessary.     

Neutron activation analysis of biological materials by the monostandard method

Instrumental neutron activation analysis by the monostandard method has been applied to the analyses of biological NBS standard reference materials; 1571 Orchard Leaves and 1577 Bovine Liver. Aluminum foils containing 0.100% gold or 2.00% cobalt were used as the monostandards. The gamma-ray spectral data were recorded on punched paper tape and were analyzed by a computer assisted data processing. The following 25 elements were determined: Al, Ca, Cl Cu, Mg, Mn, V (by short period irradiation), As, Ba, Br, Co, Cr, Cs, Eu, Fe, Hg, K, La, Na, Rb, Sb, Sc, Se, Sm and Zn (by long period irradiation). The results were compared with the certified values by NBS and the reported values in literatures to prove the reliability and accuracy of the monostandard method.     

Estimates of iodine in biological materials by epithermal neutron activation analysis

Iodine abundances in NBS biological SRMs and various organs of rats were evaluated by epithermal neutron activation analysis with a boron carbide filter. Detectability of iodine in different biological materials by this method is discussed.

     

Determination of silver in biological reference materials by neutron activation analysis

Silver in selected, predominantly biological, reference materials (NIST SRM 1515, 1547, 1549, 1566a, 1571, 1577b, 2704, CTA-OTL-1, and Bowen’s Kale) was determined using neutron activation analysis (NAA) in two different analytical modes: instrumental NAA with epithermal neutrons (ENAA), and NAA with radiochemical separation (RNAA). The ENAA mode was based on long-time 5-hour irradiation of samples in a special Cd lined box with counting after 8-month decay. The RNAA procedure consisted in 20-hour irradiation of samples, their decomposition/dissolution by alkaline-oxidative fusion, and precipitation of AgCl including several purification steps. Both methods provided Ag contents in the analyzed reference materials consistent with certified and/or literature values down to the ng·g⁻¹ level.     

Determination of Hg in biological samples by substoichiometric neutron activation analysis

The method described here involves the irradiation of biological samples and a g quantity of standard with thermal neutrons at the self-serve position in the CIRUS reactor, followed by dissolution of the sample and standard in the presence of milligram amounts of carrier. Both the sample and the standard are subjected to substoichiometric extraction under controlled experimental conditions with ethyl thioacetoacetate into chloroform. An aliquot of the organic phase is counted on a -spectrometer. The concentration of Hg in various biological samples and the accuracy, precision, and sensitivity of the method are discussed.     

Neutron activation analysis of iodine in soil

A simple pre-irradiation procedure for the separation of iodine from soil has been developed. A soil sample was heated in a quartz tube for 15 min at about 900 °C. The evaporated iodine was collected in activated charcoal, which was produced from phenol resin with low impurities. The charcoal, with sorbed iodine, was irradiated by neutrons and the¹²⁸I produced was measured. A successful elimination of the background radioactivity due to the matrix elements was possible with this separation procedure. The detection limit by this method for soil samples was about 0.1 mg/kg (dry). The method has been applied to analyze selected soil samples.     

Determination of copper in biological samples by substoichiometric neutron activation analysis

A method has been described for the determination of trace amounts of copper in biological samples by thermal neutron activation analysis, involving radiochemical separation of copper from irradiated matrix employing substoichiometric extraction of Cu/II/ with 2-mercaptobenzothiazole /2-HMBT/ into chloroform. 4.01 g of Cu/II/ can be determined with an accuracy of 3.13% and precision of 1.08%.     

Neutron activation analysis on ancient Greek silver coins and related materials

66 archaic Greek silver coins have been analyzed for the minor elements Cu, Au, Bi and Pb, and for the trace elements Na, Mn, Co, Ni, As, Sn, Sb and Ir. Instrumental neutron activation has been used for the determination of Cu and Au and atomic absorption spectroscopy for Pb and Bi. The trace elements could be detected only after a separation of the interfering matrix activities by an extraction with a diethyl-dithio-carbamate complex. The homogeneity of Au and Cu in the coins and the significance of the trace elements are discussed. The statistical evaluation of the analytical data reveals distinct groups for coins of some provenances.     

Deuteron activation analysis of carbon in gallium arsenide using substoichiometric precipitation

Ultra trace carbon in gallium arsenide has been determined by deuteron activation analysis. It consists of steam distillation of nitrogen as ammonia and successive substoichiometric precipitation as ammonium tetraphenylborate. It is confirmed that nitrogen is precipitated substoichiometrically as ammonium tetraphenylborate in spite of the various chemical species of¹³N. The procedure developed was applied to the deuteron activation analysis of carbon in carbon-doped and undoped gallium arsenides. It took 30 minutes from the end of irradiation to the start of the radioactivity measurement. The detection limit of carbon in gallium arsenide was as low as 1 ppb.     

Determination of oxygen in gallium arsenide by3He activation analysis using substoichiometric precipitation

Distillation of fluoride as fluorosilicic acid and substoichiometric precipitation as lanthanum fluoride was studied for the determination of oxygen in gallium arsenide by³He activation analysis. Fluoride could be separated substoichiometrically with a good reproducibility by two distillations and successive precipitation with lanthanum. The oxygen concentration in gallium arsenide prepared by the horizontal Bridgman technique was 10 to 36 ppb and increased a little along the front, middle and tail portions in the crystal.     

Epithermal instrumental neutron activation analysis of biological reference materials for iodine

Epithermal instrumental neutron activation analysis (EINAA) methods have been optimized and applied to several biological reference materials and selected food items for the determination of iodine. The method involves irradiation of the samples for different periods in epi-cadmium and/or epi-boron flux of the Dalhousie University SLOWPOKE-2 reactor and direct counting without any pre-treatment on a 25-cm³ hyperpure Ge detector. The 443 keV photopeak of ¹²⁸I is used for assaying the iodine content. Precision of measurements, expressed as the relative standard deviation, is 10–15% at 200–500 ppb and 3–12% at 500–6000 ppb levels of iodine. Accuracy of iodine measurements is within 5%. The detection limits for iodine in several biological materials with cadmium and boron, either alone or a combination of the two, as thermal neutron shields have been found to vary between 0.1 and 0.4 mg · kg^–1 for different periods of irradiation, decay and counting. The results suggest that the EINAA methods can be successfully applied to biological materials for routine analysis of iodine at levels higher than 200 ppb.     

Determination of iodine in reference materials by activation analysis

A rapid radiochemical procedure for the separation of iodine has been devised, which is characterized by extremely high decontamination factors so as to give pure¹²⁸I spectra with biological materials containing large concentrations of interferring elements such as sodium, bromine and chlorine. The method is based on ignition in oxygen followed by an oxidation-reduction and extraction-stripping cycle involving nitrite, sulfite and carbon tetrachloride. Results are presented for ten NBS and IAEA reference materials, frequently referred to in the literature. This work was done in partial fulfilment of the requirements for an M.Sc. degree (I. Gvardjančič).     

Testing the accuracy of neutron activation analysis of silver in biological materials

While silver can be efficiently collected from biological materials into lead beads by conventional fire assay, reagent blanks make this method unsuitable for determining the metal at concentrations less than 1 ppm. A radiochemical neutron activation analysis method is described which avoids this problem and can give reliable results down to 1 ng g^–1. The method has been tested using various reference materials /RM/, and it is concluded that NIES Mussel and Pepperbush are the best characterised RMs for determining traces of silver.     

Neutron activation analysis of semiconductor materials

Two examples of the use of neutron activation analysis for the characterization of semiconductor materials are given. 23 elements were determined in ASTM silicon intercomparison samples. Most elements are below the detection limits, which vary between 0.009–300 ng/g. CdS/CdTe thin films have been characterized by determining the Cd, Te, Cl, I and In concentrations of dissolved films. Parallel determinations in different samples of films prepared under identical conditions agreed within 0–53% (average deviation 21%) for Cl, Cd, In and I in CdS and 1.6–22% (average 8.7%) for Cd and Te in CdS/CdTe, respectively. It was determined both by NAA and resonance ionization spectrometry (RIS). The order of magnitude of the results was 1 ng/g and they agree within the range 7–64% (average difference 25%). The analytical procedures are described and discussed.     

Determination of iodine in milk products and biological standard reference materials by epithermal neutron activation analysis

The biologically essential trace element, iodine, has been determined in various milk products by epithermal neutron activation analysis /ENAA/ after sealing in quartz and irradiating under cadmium cover. The method was extended to several IAEA and NBS biological reference materials.     

Semi-automated determination of iodine in biological fluids by activation analysis

A simple automated system has been built that permits the selective separation of radioiodine by ion-exchange in eight samples simultaneously and the regeneration of the resin columns in fifteen minutes. Iodine is subsequently determined by γ-spectrometry.     

Neutron activation analysis of manganese in biological samples

The ordinary histopathological technique utilizing an automatic tissue processor was studied to remove interfering elements of sodium and chlorine so that nondestructive neutron activation analysis of tissue could be accomplished. The manganese values obtained by this method were found to compare favorably with other methods. Deceased.