Comparative study of pertechnetate reduction by thiourea using spectrophotometric,solvent extraction and ion-exchange methods

The results of a comparative study of pertechnetate reduction by thiourea in mineral acid (HCl, HNO₃, HClO₄, H₂SO₄) media using spectrophotometric, solvent extraction and ion-exchange chromatographic methods are presented. Changes of spectral characteristics of redox systems and distribution characteristics of reduced technetium (cationic) forms on extraction with bis(1,2-dicarbollide)cobaltic acid and on ion exchange on Dowex 50WX8 were established as a function of time and either aqueous or organic phase composition. Thiourea was tested as a reagent for reduction back-extraction of technetium from organic phases containing the amines Aliquat 336 and trilaurylmethylammonium as convenient extraction reagents for pertechnetate.     

Electrochemical studies of technetium at a mercury electrode

The electrochemistry of technetium was studied by polarography, cyclic voltammetry and coulometry in chloride and sulfate media as a function of pH in the range 1.5–13. Compounds of Tc(III) and Tc(IV) are produced by reduction of pertechnetate, and the system Tc(III)/Tc(IV) was investigated in acidic media. The potential—acidity diagram of technetium is described for two total pertechnetate concentrations. Evidence for the dismutation of Tc(III) below pH 4 is discussed.     

A new method for the spectrophotometric determination of pertechnetate with tris(1,10-phenanthroline)iron(II) ion

A new spectrophotometric determination of technetium has been developed by means of the solvent extraction of tris(1,10-phenanthroline)iron(II) ([Fe(phen)₃ ²⁺]) with pertechnetate into nitrobenzene. The concentration of technetium can be determined by measuring the characteristic absorbance at 516 nm (=11,700M^–1·cm^–1) in the organic phase. An important feature of the proposed method is that the concentration of pertechnetate can be determined without complicated processes such as the reduction of pertechnetate and the subsequent formation of a colored chelate.     

Synthesis of tris(β-diketonato) technetium(III) and its adsorption behaviour on silica gel

Tris (benzoylacetonato) technetium(III) and tris (2-thenoyltrifluoroacetonato) technetium(III) were synthesized by the direct reduction of pertechnetate with dithionite in the presence of excess ligands. The geometrical isomers of the benzoylacetonate were further separated by means of a silica gel column chromatography. In the silica gel system, the adsorption distribution coefficient of the tris (-diketonato) technetium(III) decreases in the order of Tc(acac)₃>fac-Tc(bzac)₃>mer-Tc(bzac₃)>Tc(tta)₃.     

Preparation of technetium metal by thermal treatment under argon/H<Subscript>2</Subscript>O

A new method for the preparation of Tc metal from pertechnetate is described. Metallic technetium was prepared from TcO₄⁻ by initial reduction in dry argon atmosphere at 300 °C followed by a wet argon atmosphere in the presence of carbon between 700 and 910 °C. The higher temperature conditions in the presence of H₂O and carbon form H₂ and CO, which can drive the reduction of TcO₂. This method was applied to the recovery of pertechnetate sorbed on anion-exchange resins resulting in the formation of Tc metal microspheres. The resulting Tc was characterized by XRD analysis and SEM.     

Preparation of Tc-HA complex by displacement of thiourea from the hexakis(thiourea-S)technetium(III) complex

The complexation of technetium with humic acid is usually done by a reduction of pertechnetate by Sn²⁺ ions. A Tc-HA complex can be scavenged in a Sn-HA complex, if tin is present as reductant. The main aim of the study was a preparation of the Tc-HA complex without impurities of Sn ions or other metal reductant, which was performed by a ligand exchange with hexakis(thiourea-S)technetium(III) under nitrogen atmosphere at pH 5.5. The [Tc(tu)₆]³⁺ complex was prepared from TcO₄ ^- in acidic solution with thiourea as a reductant. Presence of the Tc-HA complex and other technetium species was determined by gel chromatography, paper chromatography and dialysis. Yield of Tc-HA complex was about 80% and reaction mixture contains about 20% of technetium dioxide, which is a side product of ligand-exchange.     

First evidence for the formation of technetium oxosulfide complexes: synthesis, structure and characterization

The reaction of tetrabutylammonium pertechnetate with bis(trimethylsilyl) sulfide in solution was studied by UV-Visible spectroscopy and mass spectrometry. Experimental results and density functional calculations provide the first evidence for the formation of a TcO(3)S(-) precursor. Larger scale synthesis afforded a solid that was characterized by EDX and XANES spectroscopy. XANES showed the presence of technetium in tetravalent state. EDX indicated the solid contained technetium, sulfur and oxygen.     

Ion exchange and solvent extraction of the thiourea complex cation of technetium-99 from mineral acid solutions

Sorption of macroamounts of the technetium thiourea complex cation by a cation exchange resin was studied in HNO₃ and HClO₄ solutions as a function of the concentration and reaction time for pertechnetate with thiourea. The distribution ratio reaches the value of 10³ and may be even higher (>10⁴) when sorption proceeds from a solution of the solid complex in dilute perchloric acid. The complex cation is extracted from 0.25–1M HNO₃ with solutions of the bis(1,2-dicarbollyl)cobalt(III) anion in nitrobenzene—chloroform (1:1), log D=2.75−2.95 being obtained. The preconcentration and separation of technetium on cation exchangers from dilute mineral acids would seem to be one field of application.     

Determination of technetium-99 from complex matrix

This paper reports an approach that can be used for efficient separation and determination of ⁹⁹Tc (as pertechnetate) after contamination of the environment by nuclear materials. The samples were decomposed by fusion in a mixture of potassium hydroxide and potassium nitrate. After fusion, technetium remains as the pertechnetate anion (TcO₄ ^?). The technetium was isolated from the sample by technique combining solvent extraction, anion exchange, then, again, solvent extraction. After separation, ⁹⁹Tc was measured by isotope-dilution mass spectrometry with ⁹⁷Tc as spike. This method yielded nanogram detection limits for ⁹⁹Tc.     

Neutron activation analysis of radiopharmaceuticals

In order to understand the chemical form of soluble technetium in paddy soil and its availability to a rice plant, soil incubation and uptake experiments have been carried out using^95mTc as a tracer. The chemical form of the soluble Tc was observed by gel chromatography and found not to be pertechnetate, but rather to be associated with soluble organic matter. An uptake experiment with rice seedlings using nutrient solution showed that this Tc-organic matter complex was less available than pertechnetate.     

Chromatographic characterization of electrochemically generated technetium-HEDP skeletal imaging agents

Reduction of pertechnetate [(99m)TcO(-)(4)] by controlled-potential coulometry in the presence of 1-hydroxy-1,1-ethanediphosphonate (HEDP) leads to the formation of (99m) Tc complexes which are suitable for bone imaging. The complex radiopharmaceutical mixtures can be separated into their respective components by anion-exchange high-performance liquid chromatography. The distribution of the complexes in the mixtures is dependent on the cell potential, pH, technetium concentration, and presence or absence of air. A single component formed in high yield and isolated from the mixture by HPLC was investigated as a potential bone-imaging agent. This particular complex is produced only in low yields when prepared by chemical reduction of (99m) TcO(-)(4). Thus electrochemistry shows promise in aiding in the development of a more efficacious bone-imaging agent by allowing selective generation of individual (99m) Tc-HEDP complexes.     

Extraction of pertechnetate by triphenyltin chloride and trioctyltin chloride

The extraction of pertechnetate in form of ionogene associates with triphenyltin and trioctyltin cations into chloroform, benzene, toluene and nitrobenzene was studied. As aqucous phases solutions of^99mTcO ₄ ^? in deionized water and in diluted solutions of NaCl, HCl, NaNO₃, HNO₃ NaClO₄, HClO₄ and NaOH were used. Concerning the organic phases, at the use of triphenyltin chloride the extractibility of pertechnetate increases in the sequence: toluene «chloroform, benzene nitrobenzene and approximately in the sequence: NaOH<NaCl, HCl<NaNO₃<H₂O<NaClO₄ concerning aqueous phases. For trioctyltin chloride in chloroform the extractibility of TcO ₄ ^? increases approximately in the sequence of aqueous phases: NaOH<HCl, NaNO₃, NaClO₄, NaCl«H₂O and in nitobenzene in the sequence NaOH<NaClO₄<HCl<NaNO₃, NaCl«H₂O. The extractibility for trioctyltin chloride is in general slightly lower as compared with triphenyltin chloride. The results of the extraction are presented in the form of graphical plots of technetium distribution ratio (D _Te′ logD _Tc) or extraction yield (E _Tc, %) against concentration of the investigated component in aqueous or organic phase. In some of the systems of the systems studied practically quantitative extraction of pertechnetate into organic phase has been achieved.     

Transfer of Technetium from Paddy Soil to Rice Seedling

Tracer experiments on the chemical transformation of technetium in paddy soil and the transfer to rice seedlings have been carried out using ^95mTc as a tracer. Two common Japanese soils, Andosol and Gray lowland soil were used in the soil incubation experiments. The chemical form of soluble Tc in soil water was a mixture of Tc-organic matter complex, Tc-iron complex and pertechnetate. An uptake experiment with rice seedlings using nutrient solution showed that the Tc-organic matter complex was less available than pertechnetate or the Tc-iron complex. These chemical forms of Tc were also observed in the root bleeding sap of rice seedlings when introduced to the nutrient solution containing soluble Tc. These results suggested that the transfer of technetium from soil to rice would depend on the chemical form of Tc and they would transport from the root to the leaf without chemical transformation.     

Feed Adjustment Chemistry for Hanford 101-SY and 103-SY Tank Waste: Attempts to Oxidize the Non-Pertechnetate Species

More than 50% of the technetium in Hanford 101-SY and 103-SY tank waste is not pertechnetate (TcO₄ ^–). These non-pertechnetate species (TcN) are stable, soluble, reduced complexes of technetium. In order to remediate these waste, it will be necessary to oxidize these species to TcO₄ ^–. For radioanalytical purposes, oxidation requires digestion in Ce(IV)/16M HNO₃. Many oxidants are ineffective. Sodium peroxydisulfate, sodium peroxydisulfate/silver(I), and ozone oxidize all of the technetium species to pertechnetate.     

On the mechanism of the electrochemical reduction of TcO 4 −1 ion on platinum cathode in sulphuric acid solutions

Electroreduction of oxygen-containing anions of the elements of VII group of periodic table, in particular, technetium is a very complicated process. The structure of electron shells of technetium 4d⁶ 5s¹ (s^9/2), allows some oxidation states from +7 to −1, and shows the tendency to hydrolysis, disproportionation and to complex formation. Heptavalent state with d⁰-electron configuration and low tendency to reduction is characteristic for technetium and rhenium. We have studied the products of electroreduction of ion TcO ₄ ⁻ from sulphurous acid solutions of pertechnetate on platinum cathode using electrophoresis, methods of classic preparation chemistry, electron and vibratory spectroscopy. As a result we have succeeded in the isolation of the products of electrochemical reactions, identification and explaining some features of the process connected with the formation of metalic technetium and intermediate complex forms of reduced technetium.     

Base hydrolysis of halobis/8-quinolinolato/ oxotechnetium/V/ complexes

Reaction mechanism of base hydrolysis of halobis/8-quinolinolato/oxotechnetium (V) /TcOX (ox)₂ X=Cl and Br/ was investigated by means of solvent extraction and spectrophotometric methods. Furthermore, distribution coefficients of tris/acetylacetonato/technetium/III/, dichlorobis/8-quinolinolato/technetium/IV/ and TcOX/ox/₂ between chloroform and aqueous solutions were determined. In an alkaline solution, TcOX/ox/₂ decomposed to pertechnetate as a final product. On the basis of the established base hydrolysis, the respective rate constants were determined.     

A method for the determination of technetium in environmental waters

A method is described which can be used to determine technetium-99 levels in a range of water types. Ruthenium isotopes which may interfere in the analysis are removed from the sample by precipitation before concentration of pertechnetate onto an ion-exchange column. Other nuclides can be removed from the column using NaOH before elution of the technetium using NaSCN. The technetium in the NaSCN eluent can then be extracted into butan-2-one which can be evaporated onto a planchette. Technetium-99m is used as a yield tracer and after this has decayed away to negligible levles the amount of technetium on the planchette can be determined by measuring the rate of beta radiation emission from the final concentrate.     

Technetium complexes with triazacyclononane

[NBu4][TcOCl4] reacts with ethylene glycol and 1,4,7-triazacyclononane (tacn) in MeOH under the formation of the deep-blue oxotechnetium(V) cation [TcO(OC2H4O)(tacn)]+, which can readily be oxidized by air to give the stable technetium(VII) compound [TcO3(tacn)]+. The reaction with aqueous HCl results in reduction and the formation of the cationic technetium(III) complex [TcCl2(OH2)(tacn)]Cl. The products were isolated in crystalline form and studied spectroscopically and by X-ray diffraction.     

Examination of a portable99Mo/99mTc isotope generator /SUBLITECHR/

Three SUBLITECH^R technetium generators were milked and generator products were tested for 5 d. Radionuclidic and radiochemical purity, pH of sodium pertechnetate solutions were -emitting impurities and pirogenity were not carried out. We can summarize that generators were running efficiently during our test period and in all cases the pertechnetate produced met the requirements of the European Pharmacopoeia.     

Reactions between technetium(VII) and some hydrazones and the spectrofluorimetric determination of technetium(VII) with 2,2′-dipyridylketone hydrazone

The reactions between pertechnetate and five hydrazones are described. Of these, the technetium(VII)/2,2′-dipyridylketone hydrazone system was found to be most sensitive, and is studied in detail. Spectrofluorimetric procedures for the determination of technetium(VII) over the range 0.01–12 mg l^?1 are reported. The reaction proceeds most favourably under acidic conditions (1.4 M hydrochloric acid). For 1 mg l^?1 technetium(VII), 100 mg l^?1 levels of U(VI), Re(VII), Mo(VI) or W(VI) do not interfere when the reaction proceeds at room temperature. Sensitivity improves at higher temperatures.