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Abstract  

A selective liquid scintillation method is proposed for the determination of uranium in geological samples by -counting. This method permits the determination of uranium in presence of other radionuclides. The extraction of uranium with HDEHP into the scintillator is conducted in the presence of DTPA in the aqueous phase. The optimum conditions provide quantitative extraction of uranium while masking the other -emitters.

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Abstract  

The liquid-liquid extraction behaviour of mercury(II) as bromide, iodide and thiocyanate has been investigated in different oxygenated and non-oxygenated solvents. The effects of the molarity of acids, their sodium or potassium salts, the concentration of Hg(II) ions, the temperature and masking anions have been studied. The possibilities of separation of Hg(II) from Zn(II), Cd(II) Tl(I), Tl(II) and Au(III) in these extractions are discussed.

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Abstract  

A first derivative spectrophotometric method has been developed for the simultaneous determination of uranium(VI) and thorium(IV) when present in the same solution using 4-(2-tiazolylazo)resacetophenone oxime (TARPO) as analytical reagent without prior separation of any of the metals or using masking agents, etc. The method allows the determination of uranium and thorium in their mixtures in the range of 0–10 ppm each. Many common anions and cations even in large quantities do not interfere.

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Abstract  

The use of the antibiotic agent tetracycline for analytical purposes in solvent extraction procedures is presented. Individual extraction curves for the lanthanides, zinc, scandium, uranium, thorium, neptunium and protactinium were obtained. Separation of those elements one from another, and of uranium from selenium, bromine, antimony, barium, tantalum and tungsten was carried out. In all cases benzyl alcohol was the diluent used to dissolve tetracycline hydrochloride. Sodium chloride was used as supporting electrolyte for the lanthanide separations and sodium perchlorate for the other elements mentioned. Stability or formation constants for the lanthanide complexes as well as for thorium complex with tetracycline were determined by using the methods of average number of ligands, the limiting value (for thorium), the two parameters and the weighted least squares. For the lanthanides, the stability constants of the complexes Ln(TC)3 go from 9.35±0.22 for lanthanum up to 10.84±0.11 for lutetium. For the Th(TC)4 complex the formation constant is equal to 24.6±0.3. Radioisotopes of the respective elements were used for the determinations. When more than one radioelement was present in an experiment, a multichannel analyser coupled to Ge(Li) or NaI(Tl) detectors was used for counting the activities. When only one radioisotope was used, counting of the radioisotopes was made with a single-channel analyser (integral mode counting) coupled to a NaI(Tl) detector. Uranium was determined by activation analysis (epithermal neutrons). Radioisotopes of the elements were obtained by irradiation in the IPEN swimming-pool reactor. The natural radioisotope2 3 4Th was used as label in the thorium experiments. In some separation procedures such as in the case of the pair uranium-neptunium, and of the pair scandium-zinc, the separation was obtained by properly adjusting the pH value of the aqueous phases, before the extraction operation. In other cases, addition of masking agents to the extraction system was required in order to perform the separation between the elements under study. In this way ethylenediaminetetraacetic acid (EDTA) was used as masking agent for scandium and the lanthanides in order to allow separation of uranium from those elements. Diethylenetriaminepentaacetic acid (DTPA) was used as masking agent for thorium in order to extract uranium into the organic phase. Separations of protactinium from thorium, and of uranium from protactinium and thorium, were accomplished by using sodium fluoride as masking agent for protactinium and DPTA as masking agent for thorium and protactinium at the same time. In the case of the separation of the lanthanides one from another it is necessary to resort to a multi-stage extraction procedure since the stability constants for those elements are too close.

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, A.: Surgical masks: evidence, image, and art. Br. J. Anaesth., 2007, 99 , 918. Perel A. Surgical masks: evidence, image, and art Br. J. Anaesth

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fluctuations on parasites of California red scale, Aonidiella aurantii (Mask.) (Hom., Diaspididae) in Alexandria. J. Applied Entomology 106, 183–187. Population fluctuations on parasites of California red scale, Aonidiella aurantii

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Abstract  

The extraction of PAN chelates of the group IB, IIB and IIIA–VA elements from aqueous solutions of pH 1–10 into chloroform has been studied radiochemically. Re-extraction studies have been made to strip the metal ions from the organic phase into aqueous solutions of KCN, HClO4 and buffer solutions. The effects of certain masking agents on the extraction of these elements have also been studied. The extraction curves indicate the possibilities of devising group chemical separation procedures for use in activation analysis.

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Abstract  

Activation analysis and autoradiography were used to investigate the concentration distribution of contaminants in poly-Si−Si3N4−SiO2−Si substrate multilayer structures (SNOS) on sampling each technological product. Samples were irradiated for 36 hrs at a thermal neutron flux of 4·1013n·cm−2·sec−1. The thin films of the analysed sample were removed stepwise by selective chemical etching using appropriate masking techniques. Simultaneously autoradiographs were made of the surface of parallel samples activated under the same conditions. The concentration of the technological contaminants (e.g. Na, Cu, Au) increases in the junction interface of the layers as unambiguously shown by the results obtained.

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Abstract  

Extraction behaviour of the chelates of group VB–VIIB and VIII elements using 1-(2-pyridylazo)-2-naphthol (PAN) has been studied as a function of pH. Studies have been made to back-extract the metal ions from the organic phase into the aqueous solution containing the optimum concentration of KCN and HClO4 and buffers of appropriate pH. The masking agents such as citrate, cyanide, thiosulphate, fluoride and thiourea were used to achieve more specific separations. The studies indicate the potentiality of PAN as a useful solvent extracting reagent in devising group chemical separation procedures for activation analysis.

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Abstract  

A rapid analytical method, applicable for the selective separation and determination of90Sr and89Sr in river water, is described. Strontium is extracted from the water sample at pH 10.5 by TTA/TOPO in cyclohexane in the presence of Tiron as masking agent for interfering ß-emitters. Radiostrontium is measured by liquid scintillation after back-extraction into 1N nitric acid. The distribution coefficient of strontium is over 400 and the separation factors from other radionuclides are higher than 5.0×103.

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