Volume 100, Issue 6 -

A new ratio primary reference measurement procedure (RPRMP), i.e. a definitive method for the determination of iron in biological materials, was devised. It is based on a combination of neutron activation with selective and quantitative post-irradiation separation of 59 Fe from all accompanying radionuclides followed by γ -ray spectrometric measurement. The novel separation scheme, involving the use of column chromatography on two (anion and cation) exchange columns, was extensively checked using radioactive tracers and was shown to be very selective and truly quantitative. High selectivity of the separation scheme was achieved by exploiting the “anomalous” sorption of Fe(III) on medium cross-linked sulfonic cation exchanger from concentrated hydrobromic acid solution. The accuracy of the RPRMP was demonstrated by the analysis of several certified reference materials. The method was used for the analysis of the three INCT CRMs based on tobacco leaves in which Fe was originally not certified, because widely discordant results by different analytical techniques were obtained in world-wide intercomparisons. The results by RPRMP in those materials were in a very good agreement with our own results by INAA. Tentative certified values (TCV) for Fe were proposed as a combination of RPRMP and INAA results. Some possible sources of systematic errors in other analytical methods were discussed.

Stability constants were determined for the complexes formed from two stereognostically designed ligands and the f -block elements Nd(III), Np(V), and Pu(VI). The ligands investigated were tris [3-(2-carboxyphenoxy)propyl]amine (NPB) and tris - N , N ´, N ´´-[2-(2-carboxy-4-ethyl-phenoxy)ethyl]-1,4,7-triazacyclononane (EETAC). A stereognostically blind ligand, nitrilotriacetic acid (NTA), was also investigated for comparison. The results suggest that there is no significant stereognostic effect for complexation of NPB or EETAC to Np(V). On the other hand, a modest stereognostic effect is seen for the NPB ligand when complexed to Pu(VI), leading to an approximately 8-fold increase in the binding strength. A more significant effect is observed for the EETAC system in which a 250-fold increase in binding is observed for Pu(VI) vs. Nd(III).

The current interest in functionalized calixarenes with phosphorylated pendant arms resides in their coordination ability towards f elements and capability towards actinide/rare earth separation. Uranyl cation forms 1:1 and 1:2 (M:L) complexes with a tetra-phosphinoylated p-tert -butylcalix[4]arene, B 4 bL 4 : UO 2 (NO 3 ) 2 (B 4 bL 4 ) n · x H 2 O ( n = 1, x = 2, 1 ; n = 2, x = 6, 2 ). Spectroscopic data point to the inner coordination sphere of 1 containing one monodentate nitrate anion, one water molecule and the four phosphinoylated arms bound to UO 2 2+ while in 2 , uranyl is only coordinated to calixarene ligands. In both cases the U(VI) ion is 8-coordinate. Uranyl complexes display enhanced metal-centred luminescence due to energy transfer from the calixarene ligands; the luminescence decays are bi-exponential with associated lifetimes in the ranges 220 μs < τ s <250 μs and 630 μs < τ L < 640 μs, pointing to the presence of two species with differently coordinated calixarene, as substantiated by a XPS study of U(4 f 5/2,7/2 ), O(1 s ) and P(2 p ) levels on solid state samples. The extraction study of UO 2 2+ cation and trivalent rare-earth (Y, La, Eu) ions from acidic nitrate media by B 4 bL 4 in chloroform shows the uranyl cation being much more extracted than rare earths.

This study investigates multiple equilibria related to the formation of the U(VI)-salicylate complex in a pH range of 3.0–5.5 using UV-Vis absorption and fluorescence measurement techniques. The absorbance changes at the characteristic charge-transfer bands of the complex were monitored, and the results indicated the presence of multiple equilibria and the formation of both 1:1 and 1:2 (U(VI):salicylate) complexes possessing bi-dentate chelate structures. The determined step-wise formation constants (log  K 1:1 and log  K 1:2 ) are as follows: 12.5 ± 0.1 and 11.4 ± 0.2 for salicylate, 11.2 ± 0.1 and 10.1 ± 0.2 for 5-sulfosalicylate, and 12.4 ± 0.1 and 11.4 ± 0.1 for 2,6-dihydroxybenzoate, respectively. The molar absorptivities of the complexes are also provided. Furthermore, time-resolved laser-induced luminescence spectra of U(VI) species demonstrate the presence of both a dynamic and static quenching process upon the addition of a salicylate ligand. Particularly for the luminescent hydroxouranyl species, a strong static quenching effect is observed. The results suggest that both the UO 2 (HSal) + and the U(VI)–Sal chelate complexes serve as ground-state complexes that induce static quenching. The Stern–Volmer parameters were derived based on the measured luminescent intensity and lifetime data. The static quenching constants (log  K S ) obtained are 3.3 ± 0.1, 4.9 ± 0.1, and 4.4 ± 0.1 for UO 2 2+ , (UO 2 ) 2 (OH) 2 2+ and (UO 2 ) 3 (OH) 5 + , respectively.

Four pillared metal(IV) phosphate-phosphonate ion exchange materials were synthesized and characterized. Studies were conducted to determine their affinity for the lanthanides (Ln´s) and actinides (An´s). It was determined that by simply manipulating the metal source (Zr or Sn) and the phosphate source (H 3 PO 4 or Na 3 PO 4 ) large differences were seen in the extraction of the Ln and An species. K d values higher than 4×10 5 were observed for the AnO 2 2+ species in nitric acid at pH 2. These basic uptake experiments are important, as the data they provide may indicate the possibility of a separation of Ln´s from An´s or even more notably americium from curium and Ln´s.

The distribution behaviour of the trivalent europium ion at a micro-component scale, between barium sulphate and aqueous solution, was studied at ambient temperature. Experiments were carried out using radioactive tracers. Results indicate an enrichment of the micro component in the solid phase relative to the solution. The effects of the concentrations of the micro and macro-elements on the coprecipitation have been examined. Europium distribution coefficient D Eu increases from 1.1 ± 0.2 to 3.2 ± 0.4 when initial europium concentration decreases from more than 17 × 10 −5 to 1.4 × 10 −5  M, in sulphuric media with SO 4 2− in excess or C Ba 2+ / C SO 4 2− < 1. The excess of barium in opposite, results in a decreasing D Eu . The coprecipitation of europium with barium sulphate as a heterovalent solid-solution is described by heterogeneous model obeying the Doerner and Hoskins logarithmic partition law. The weaker partition coefficients lower than unity ( λ = 0.25 when C Eu(III) ≈ 1.4 × 10 −5  M and λ = 0.13 when C Ba 2+ /C SO 4 2− < 1 and 17.8 × 10 −5 ≤ C Eu(III) ≤ 153.5 × 10 −5  M) lead to crystals increasingly enriched in the trace element.

To enable laboratory work with larger amounts of 226 Ra and its decay products, e.g. , 222 Rn and its daughters, these need to be captured in order to avoid unnecessary alpha contamination of the laboratory work space and ventilation systems. In this study, radon gas was pumped through a column filled with the silver exchanged zeolite called “silver exchanged molecular sieves 13X” (Ag 84 Na 2 [(AlO 2 ) 86 (SiO 2 ) 106 ]· x H 2 O). After exposure to radon, the radioactivity of the zeolite was measured repeatedly using high resolution gamma spectrometry. It was shown that radon was captured and retained in the silver exchanged zeolite. The zeolites´ ability to retain radon was decreased by formation of metallic silver, caused by ionizing radiation. However, the zeolite was regenerated by heating and its radon capture ability was restored. The daughters of radon are not in gas phase and will hence stay on the column.

A method of tritium introduction into different types of organic molecules that is based on the interaction of atomic tritium with solid organic target is described. Tritium atoms are formed on the hot W-wire, which is heated by the electric current. Such an approach is called “tritium thermal activation method”. Here we summarize the results of labeling globular proteins (lysozyme, human and bovine serum albumins); derivatives of pantothenic acid and amino acids; ionic surfactants (sodium dodecylsulfate and alkyltrimethylammonium bromides) and nonionic high-molecular weight surfactants – pluronics. For the first time it is observed that if the target-compound is fixed and its radicals are stable the specific radioactivity of the labeled product can be drastically increased (up to 400 times) when the target temperature is ca . 295 K compared with the results obtained at 77 K. The influence of labeling parameters as tritium gas pressure, exposure time and W-wire temperature was tested for each target temperature that results in the optimum labeling conditions with high specific radioactivity and chemical yield of the resulting compound.