[en] Low concentrations of pertechnetate (10^-7 M . L^-1 or less) can be quantitatively determined by chronopotentiometric reoxidation of the element previously enriched on a glassy carbon electrode from a 0.01 n acid solution at -700 mV (vs. Ag/AgCl). Reoxidation, during which an electrode potential of about 560 mV is dominating, may be performed either galvanostatically or without any current flow, if Ce(IV) is used as the oxidant. If, instead of Tc(VII), Tc(IV) is present, the potential-time-curve characteristic for Tc(VII) is not obtained. This fact allows the analytical distinction of both oxidation states. (orig.)

No abstract available

[en] A systematic study was carried out on the adsorption of Na, Cs and Ba on Dowex 1x8 from various concentrations of hydrochloric and nitric acid solutions. The addition of water-miscible organic solvents to the acidic solutions was found to increase the Ksub(d) values for these elements to different extents which elaborates useful methods for the separation of carrier free Ba from macro-quantities of Cs. The effect of kind and content of the different alcohols on the adsorption of Ba was also investigated. It was found that Ksub(d) increases with the increase of the alcohol content as well as with the increase of both dielectric constant and the chain length of the alcohol. This phenomenon is found to be more pronounced in case of nitric acid media. (orig.)

[en] Submicrogram-amounts of Np-237 in process-solutions of the MILLI-plant are determined by neutron activation analysis after chemical separation from nuclear fuel elements and fission products by extraction with thenoyl-trifluoro-acetone. Chemical yield controls are established by adding and measuring of Np-239 spike activity. (orig.)

[en] Low concentrations of technetium have been measured DP-stripping-voltammetrically using a carbon paste electrode modified with tri-n-octylamine (TOA-CPE). Preconcentration of the metal ion on the electrode surface accomplished by dipping of the latter in the sample solution which is 2M in HCl, relies on the chemical reaction with the amine acting as a liquid anion exchanger. Both, Tc-IV occurring as the TcCl₆^2- ion in chloride solutions as well as Tc-VII hereby are deposited. Measurements following deposition yield voltammograms of essentially different shapes for the two Tc species. With Tc-IV a characteristic curve with a prominent current signal at -280 mV (vs. Ag/AgCl) is obtained which can be evaluated for Tc quantitation. However, starting from Tc-VII, complex voltammograms are registered not allowing direct technetium assays. Nevertheless, after reduction to Tc-IV, e.g. by means of ascorbic acid, also Tc-VII can be quantified reliably by the method described, the lower detection limit for both oxidation states being about 4x10^-8 M. (orig.)

[en] The polarographic behavior of tri-n-butylphosphate (TBP) in nitric acid media in general and its influence on the height of the polarographic wave of uranium in particular are discussed. After the presentation of a short review of the literature concerning this subject, results of own investigations in this field are presented. Trials undertaken with the aim of indirect polarographic determinations of TBP by means of its diminishing effect on the polarographic wave of uranium were without success, which, in view of known facts, is not surprising. (orig.)

[en] It is known that in sulfuric acid solution pertechnetate is reduced by thiocyanate to form thiocyanate complexes. After this reaction the technetium acquires the capability of being adsorbed at the hanging mercury drop electrode (HMDE) provided that a potential of -0,40 V (vs. Ag/AgCl) has been applied to the electrode. If, by application of the differential pulse voltammetry after the phase of deposition the potential at the electrode is scanned cathodically, traces of technetium can be determined very sensitively by evaluation of the peak current recorded at minus 1,27 V (Ag/AgCl). The effect is still being enhanced by the presence of not interfering small perrhenate amounts. The reproducibility of the measured values is excellent. (orig.)

[en] The possibility of enrichment as well as the stripping voltammetric behavior of technetium traces at a carbon paste electrode modified with thenoyltrifluoroacetone (TTA) was studied. Accumulation of Tc(IV) on the electrode surface occurs without application of a deposition voltage due to complex formation with TTA, probably resulting Tc(TTA)₄. During the following cathodic potential scan made with the differential pulse mode a characteristic current peak is obtained at -40 mV (vs. Ag/AgCl) which increases with Tc concentration and deposition time. However, Tc(IV) gives much more sensitive stripping current signals if a reductive deposition potential of -0.4 V is applied, presumably on account of the formation of Tc(TTA)₃. In this case an anodic voltammetric scan was applied resulting a stripping peak at about +30 mV, the height of which is related to the concentration of Tc in solution as well as to the time of deposition. Calibration graphs revealed good reproducibility for analytical application. The lower detection limit for Tc(IV) achieved for 1 M sodium chloride solutions 4.6 x 10^-9M. Tc(VII) is not enriched in the absence of reduction which takes place only from about -0.6 V on with the pH optimally set at 3.5. Therefore it is basically possible to discriminate Tc(IV) from Tc(VII). (orig.)

No abstract available

[en] Tetraphenylarsonium chloride (TPAC) as a specifically complexing reagent for pertechnetate ions has been immobilized on the surface of a glassy carbon disk electrode (GCE) by means of a copolymer film prepared from vinylpyridine and vinylferrocene. Immobilization was obtained by anionic exchange reaction between TPAC carrying a negatively charged sulfo group and the pyridine groups quaternized with methyl iodide on the copolymer electrodeposited at the electrode material. This procedure permitted chemical preconcentration of technetium on the electrode surface. After the enrichment step a cathodic stripping voltammetric scan in the DP mode was applied, during which a current peak at -750 mV (vs. Ag/AgCl) was registered, likely due to the reduction of Tc(VII). The influence of different electrode modification procedures on the height of the stripping peak was examined. The dependence of the signal height on the electrode coverage with the quaternized copolymer, the reaction time for incorporation of the sulfonated ligand, the enrichment time of technetium, and the pH and composition of the measurement solution are shown. A detection limit of 1x10^-8 M Tc(VII) could be reached in an alkaline and rather dilute NaCl solution after 5 min enrichment time. (orig.)