The determination of medium and long-lived nuclides can be combined with short-lived ones if a medium or long irradiation is made prior to the short irradiation and radiochemical processing. Thus, an RNAA method previously developed for determination of iodine based on the reaction127I(n,)128I (T1/2=25 m) using oxygen flask ignition of the irradiated sample, followed by solvent extraction with an iodine-iodide redox cycle, was combined with an overnight preirradiation to induce the235U fission product133I (T1/2=20.8 h). By reactivating the sample, cooled 1–2 days after the first irradiation, for few minutes both128I and133I could be quantified in the separated iodine fraction. Non-combustible inorganic materials (e.g., sediment, soil, etc.) can be successfully ignited after mixing with excess cellulose powder. Chemical yields for iodine were determined spectrophotometrically in the organic phase, while homogeneously spiked Whatman cellulose powder was used as uranium standard. Mercury is also released on ignition and collected in the absorbing solution, from where it was separated by toluene extraction. Its chemical yield was determined for each aliquot using203Hg tracer and counting on an LEPD. Results for some suitable SRMs are presented, and the general features of the double irradiation technique discussed.
A derivative form of NAA is proposed which is based on the use of an endogenous internal standard of already known concentration in the sample. If a comparator with a known ratio of the determinand and endogenous standard are co-irradiated with the sample, the determinand concentration is derived in terms of the endogenous standard concentration and the activity ratios of the two induced nuclides in the sample and comparator. As well as eliminating the sample mass and greatly reducing errors caused by pulse pile-up and geometrical differences, it was shown that in the radiochemical mode, if the endogenous standard is chosen so that the induced activity is radioisotopic with that from the determinand, the radiochemical yield is also eliminated and the risk of non-achievement of isotopic exchange greatly reduced. The method is demonstrated with good results on reference materials for the determination of I, Mn and Ni. The advantages and disadvantages of this approach are discussed. It is suggested that it may be of application in quality control and in extending the range of certified elements in reference materials.
Authors:A. Byrne, M. Dermelj, and M. Tušek-Žnidarič
The iodinated resin technique for separation of128I directly from neutron irradiated biological fluids is attractive due to its rapidity, simplicity and high degree of radiochemical purity; however, some doubts exist about the yields of iodine which can be recovered, particularly from organically bound iodine. In the present study, chemical yields on the resin column were studied for irradiated urine, serum and milk by standard additions of iodide and thyroxine. It was found that yields are not quantitative but lie in the range 80–95%, depending on the matrix, with a variability of up to 6% standard deviation. In addition it was shown that no significant adsorption of iodine occurs on polythene ampoules from irradiated biological fluids of natural pH. Some comparative experiments between the resin technique and the oxygen flask ignition method on fluids before or after drying, respectively, showed satisfactory agreement. It is concluded that the iodinated resin technique is suitable for routine analyses or large scale screening programs.
A versatile separation system based on the extraction of dithiocarbamates and applicable to the determination of copper, managanese,
zinc and indium in a wide selection of materials by activation analysis is described. After the dissolution of the sample
and a few simple operations which eliminate specific interferences, depending upon the material (e. g. sodium and gold in
the NBS Standard Reference Glasses), carbamates are extracted under specific conditions by addition of appropriate complexing
agents and selective stripping. Extreme separation factors permit interference-free counting using a sodium iodide detector.
For example, indium is separated from a hundred thousand fold excess of manganese in the determination of the two elements
in Orchard Leaves. Results are also presented for all four elements in Bowen's Kale, NBS Bovine Liver, and for Cu, In and
Mn in the 0.02 ppm and 1 ppm SRM glasses.
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
An activation method was used to determine the mercury content of typical laboratory reagents and materials, in particular,
filter paper and substances used in the analysis for mercury. Typical values for filtering materials are in the tens of nanogram
range but in some types they can be considerably higher. Results for some other reagents also show that a thorough checking
for background levels of substances used in analysis is essential. A minor modification of the volatilization method is also
described for the analysis of substances rich in sulfur or evolving large quantities of halogen acid.
A radiotracer method is described for measurement of the chemical yield in radiochemical neutron activation analysis of selenium using the75Se (120 d) induced nuclide. It is based on81mSe (57 min) radioisotopic tracer, prepared immediately before its use in the radiochemical separation procedure, by neutron irradiation of highly enriched80Se. The recovery of selenium is calculated from the 103 keV -peak of81mSe in the separated selenium fraction used for quantitation of75Se. The technique is illustrated by results for biological reference materials of good accuracy and reproducibility.
Inorganic arsenic, MMA, DMA and arsenobetaine (As) were separated by the use of cation and anion exchange chromatography combined with neutron activation. Two complementary approaches were used: firstly, authentic, non-irradiated arsenic compounds, either singly or in mixtures, were separated and NAA of the fractions used as an element specific detection method. Secondly, the arsenic compounds were neutron irradiated under different conditions and for different times and the products separated and quantified. The76As labeled species (mono-, di and trimethylated) were then additionally used to calibrate and improve the column separations. Using the separations developed, arsenic species in samples of shrimps and the standard reference material DORM-1 were determined, after an extraction step, using ion exchange chromatography followed by INAA of the fractions collected.
Quantitative data on trace elements in two tobacco leaf (candidate) reference materials OTL-1 and VTL-2 prepared by the Polish Academy of Sciences and the Institute of Nuclear Chemistry and Technology, Warsaw, Poland, are presented and compard to recommended values, where available. By instrumental neutron activation analysis (INAA), as well as by radiochemical technique (RNAA) 30 elements were quantitatively determined and fair agreement was found between the results and recommended values for the first material.
Authors:M. Dermelj, Z. Šlejkovec, M. Šorak-Pokrajac, and M. Rossbach
The concentration levels of total iodine obtained by RNAA in different sorts of tobacco, including the reference sample Kentucky Tobacco 2RI, two new candidate reference materials, Oriental Tobacco Leaves /CTA-OTL-1/ and Virginia Tobacco Leaves /CTA-VTL-2/ prepared in the Institute of Nuclear Chemistry and Technology, Warsaw, and some biological SRMs, are presented and discussed.