An overview is presented of the characteristic features of RNAA (radiochemical neutron activation analysis). Criteria are given for comparison of RNAA with other trace-element analytical techniques. Appropriate fields of application of RNAA are indicated as well as approaches to secure the future position of the technique. Finally, some trends for further development of chemical separations in RNAA are outlined.
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 g/kg. The method has been used to determine 6.4±0.6 mg/kg phosphorus in SRM 2175 refractory alloy.
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 precipitation 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.
A RNAA method has been developed for the simultaneous determination of Rb and Cs in geological samples. The method is based on precipitation with sodium tetraphenylborate followed by NaI(Tl) gamma spectrometry. Three mica dust particulate samples and two USGS standard rocks, BCR-1 and W-1 were analyzed. Dipicrylamine (DPA) and 2-thenoyl-trifluoroacetone (TTA) in nitrobenzene were also used for solvent extraction. The precipitation method is better than solvent extraction.
Authors:C. Galinha, M. Freitas, A. Pacheco, J. Kameník, J. Kučera, H. Anawar, J. Coutinho, B. Maçãs, and A. Almeida
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.
Authors:J. Woittiez, S. Subramanian, K. Volkers, and J. De Goeij
The idea to use high performance liquid chromatography with continuous UV detection for multi-element radiochemical separation and simultaneous multi-element on-line yield determination is introduced. The validity of the concept was evaluated by demonstrating the constancy of the ratio of the signals for a main isotope (60Co) and a carrier (59Co) as a function of the elemental mass processed in the separation. The suitability of the method for practical purposes is demonstrated by its application to the RNAA determination of cobalt in biological materials. It is concluded that the method, although not yet completely developed, bears the potential of improving both accuracy and precision of multi-element RNAA.
A radiochemical neutron activation analysis (RNAA) combustion method coupled with a neutron exposure normalization technique was used to determine low g/kg mercury levels in three National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs). Two coals (sub-bituminous and bituminous) and a diet material were analyzed. The results obtained provided recommended values of approximately 5 g/kg for SRM 1548a Typical Diet, 24 g/kg for SRM 1635 Trace Elements in Coal (sub-bituminous), and 100 g/kg for SRM 1632b Trace Elements in Coal (bituminous).
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.
Authors:S. Heller-Zeisler, P. Borgoul, R. Moore, M. Smoliar, A. Suarez, and J. Ondov
The sensitivity and precision of instrumental neutron activation analysis (NAA), radiochemical neutron activation analysis (RNAA), and thermal ionization mass spectrometry (TIMS) are compared for the determination of Ir in ambient size-fractionated aerosol particulate samples. The results of the TIMS analyses indicated high analytical precision (0.2% at >50 pg Ir), but the sensitivity of detection was limited by blank values (300–500 fg). The sensitivities for INAA and RNAA were comparable, i.e., 60 to 90 fg in size-segregated particulate samples.
The concentrations of 8 REE (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in wheat and rice samples have been determined by RNAA. The contents and distributions of REE in each part of the plants (i.e. root, leaf, stem, husk and seed) and their host soils were studied, which included samples applied with rare earch elements in farming and control samples. The effects of applying rare earths on the uptake of REE by the plants and the REE accumulation in the grains on human health were also discussed in this paper.