RNAA Procedure Research Articles

Selenium determination in cereal plants and cultivation soils by radiochemical neutron activation analysis

Selenium (Se) is an essential micronutrient for human health but it is deficient in at least 1 billion people around the globe. Cereals are by far the most significant agricultural crops, not only on a gross tonnage basis, but also by what they represent in terms of energy supply and dietary intake for human nutrition worldwide. Portugal is no exception to such pattern. The Portuguese situation is difficult to assess though, due to scarce information and lack of consistent studies on the subject. In these terms, the Se status of major cereals and their cultivation soils are dealt with herein. Two species of wheat–bread and durum wheat–were sown at the end of November 2009, and then sampled in different growth stages. Rye was collected during harvest season, and cultivation soils were analyzed as well. Se results were within the range of: 100–225 ng g−1 for soils; 3–55 ng g−1 for durum wheat; 6–80 ng g−1 for bread wheat; and 4–30 ng g−1 for rye. Accuracy of the RNAA procedure was proved by analysis of reference materials NIST-SRM 1515 and NIST-SRM 8433.

Neutron activation analysis in geochemical characterization of Jurassic–Cretaceous sedimentary rocks from the Nordvik Peninsula

As a part of geophysical, stratigraphical and paleontological study aimed at precise correlation of the Jurassic-Cretaceous (J/K) boundary interval in the Tethyan and Boreal Realms, detailed magnetostratigraphic and biostratigraphic profiles with well-calibrated J/K boundary have been selected from several localities for geochemical characterization. Instrumental and radiochemical neutron activation analyses (INAA and RNAA, respectively) were employed in the characterization of a vertical profile around the supposed J/K boundary in the Boreal Realm situated on the Nordvik Peninsula, Northern coast of Middle Siberia (Laptev Sea), Russia, for which an iridium anomaly has been reported in literature. INAA enabled determination of about forty major and trace elements. An RNAA procedure for assaying platinum group elements (PGE) has been tested consisting in sample decomposition by alkaline-oxidative fusion, reduction of PGE, and pre- cipitation of their sulphides. Despite several difficulties, the procedure enabled to found Pt and Ir at ppb and sub-ppb levels, respectively, in several samples, namely in pyrite aggregates originated probably in diagenetic reductive processes following decomposition of burried organic matter. However, the existence of a pronounced PGE spike reported previously for the J/K boundary on the Nordvik Peninsula has not been confirmed.

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 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.

Simultaneous low-level determination of iodine and manganese in biological materials by radiochemical neutron activation analysis

A new RNAA procedure was developed for simultaneous determination of low levels of I and Mn in biological materials. The procedure is based on sample decomposition by alkaline-oxidative fusion in a mixture of Na2O2 + NaOH at 900°C followed by extraction of elementary iodine by chloroform. Subsequently, Mn is separated either by precipitation of hydrated MnO2 or by extraction of the Mn-diethyldithiocarbamate complex in chloroform. The accuracy of the RNAA procedure developed was proven by analysis of several low-level biological reference materials. Detection limits of I and Mn achievable in both institutes and the degree of interference for the Mn determination due to 56Fe(n,p)56Mn reaction with fast neutrons are discussed.

Determination of iodine in Asian diets by epithermal and radiochemical neutron activation analysis

Abstract Samples of diets from China, Japan, Korea, India, Pakistan and Philippines were analyzed using epithermal and radiochemical neutron activation analysis (ENAA and RNAA, respectively) within the framework of the IAEA project “Reference Asian Man”. The RNAA procedure was based on alkaline-oxidative fusion followed by extraction of elemental iodine in chloroform. The analytical methods employed are discussed in terms of detection limits and uncertainties of the results obtained. For quality control purposes a number of NIST biological reference materials, namely diets and foods were analyzed. Results for the diet samples indicate that achieving the WHO recommended daily allowance for iodine may be a problem in most of the above given countries.

Comparison of RNAA and ICP-MS for the determination of ultra-traces of Th and U in geological and cosmochemical samples

In order to determine thorium and uranium traces in geochemical and cosmochemical samples, we developed an ICP-MS procedure, in which an anion-exchange step was introduced after sample digestion to separate major matrix elements, leading to decrease the dilution factor and increase the sensitivity for Th and U. The ICP-MS procedure was compared to the RNAA procedure which we recently developed for the same purpose. Both ICP-MS and RNAA procedures developed were found to yield similar detection limits (sub ppb) for Th and U.

Measurement of Phosphorus in Metals by RNAA

An RNAA procedure has been developed for measurement of low-level phosphorus in metals. Samples are irradiated at a neutron flux of 2.7·1013 n·cm−2·s−1 then mixed with carrier and dissolved in acid. After chemical separation and purification of the phosphorus and gravimetric determination of carrier yield, 32P is determined using a beta proportional counter. The detection limit for a 0.1 g sample irradiated for 30 minutes is 5 μg/kg. The method has been used to determine 6.4±0.6 mg/kg phosphorus in SRM 2175 refractory alloy.

Low level determination of thallium in biological and environmental reference materials by RNAA using several counting methods

A new RNAA procedure was developed capable of low level determination of thallium in biological and environmental samples. After high fluence neutron irradiation in a nuclear reactor, wet ashing of samples and T1(I) separation by solvent extraction with sodium diethyldithiocarbamate at pH 13, several types of counting were employed to compare their detection limits and to utilize the self-validation principle of NAA. The following measurement modes were used: High efficiency counting of γ-rays of202T1 and Hg X-rays produced on decay of204T1 using a well-type HPGe detector, combined γ− ray and β−-counting of204T1 with the aid of a HPGe planar detector, and liquid scintillation counting and counting of Cerenkov radiation of β−-particles of204T1. The lowest detection limit of 0.034 ng of T1 was achieved on liquid scintillation counting of204T1. The method was applied for the analysis of biological NIST SRMs 1515, 1573a, 1577b and environmental NIST SRM 1633a. Good agreement was found between the thallium certified value in SRM 1633a and values determined in this work by all counting modes. For SRM 1573a, results in agreement were obtained by two counting modes, while counting of Hg X-rays of204T1 was only used for SRMs 1515 and 1577b.

RNAA for arsenic, cadmium, copper, and molybdenum in CNS tissues from subjects with age-related neurodegenerative diseases

Reactor thermal neutron irradiation of biological matrices induces high levels of intense gamma-ray or bremsstrahlung radiation from82Br,42K,24Na, and32P, that interfere with the determination of As, Cd, Cu, and Mo by INAA. Central nervous system (CNS) issue samples from subjects with Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and controls were analyzed using a simple RNAA procedure involving a rapid two-step solvent extraction procedure to determine these four elements. Significant increases (p≤0.05) in concentrations of Cd and Mo were observed for brain of AD subjects compared to controls, but significant imbalances were not observed for ALS subjects. Concentration data for these elements in selected international reference standards are also presented.

RNAA of trace iridium in Precambrian-Cambrian boundary samples by thiourea type chelate resin separation

A RNAA procedure is described for the determination of trace Ir in Precambrian-Cambrian boundary samples. After irradiation, the powdered sample is transferred to a graphite crucible to expel the massive silicon with mixed acid (HF−HCl−HNO3) by heating. The residue is then fused with mixed fusion (Na2O2−NaOH) in a muffle furnace at 700°C for 15 minutes. After cooling, the fused mixture is leached with hot water. The final solution is adjusted to pH 1.5–2.0 and then passed through a column filled with thiourea type chelate resin. The resin absorbed with192Ir is measured for 4000–10 000 s by means of SCORPIO-3000 multi-channel computer — Ge(Li) detector system. Experiments with radioactive tracer are carried aout for checking radiochemical separation yield. The accuracy and precision of the method are evaluated by the analysis of U.S. geological SRMs DTS-1 and AG-Bohor-1. The method is used for the determination of trace Ir in several sets of Precambrian-Cambrian boundary samples collected from Yunnan province in China and the Ir anomaly is observed.

Iodine in mineral waters: A comparison of results from two analytical techniques

A comparative study of the determination of iodine in mineral waters is presented. Iodine was first determined by a standard titrimetric method and the results obtained were compared with those obtained by the faster and more sensitive radiochemical neutron activation method. For a series of waters, the results obtained by the two techniques were in fair agreement for the higher concentration levels of iodine, but for very low iodine levels the titrimetric method was insufficiently sensitive. The RNAA procedure was checked by standard addition experiments, and shown to be also valid when iodine was present as iodate.

Radiochemical neutron activation analysis of rare earth elements in peridotitic rocks

The understanding of the geochemistry of basalt petrogenesis and the nature of the upper mantle requires the examination of such rocks as peridotites which in many cases are thought to represent upper mantle material. The mineralogical composition of peridotitic rocks in such that they accommodate large proportions of such trace elements as the transition elements but very small amounts of the rare earths and hygromagmaphile elements. The last two groups are often able to provide a large amount of information leading to petrogenetic models. Owing to the extremely low concentrations of the REE in peridotitic rocks it is necessary to separate them from other elements which will interfere with their precise determination. We have used a radiochemical neutron activation analytical method which is adapted from various published methods. It involves a post-irradiation sample fusion, two separate ion-exchange chromatographic stages and finally a fluoride precipitation. The RNAA procedure is capable of providing very precise REE data for perioditic samples and we have used it for the analysis of such rocks from several geodynamic environments.