Isotope Effects of Samarium and Ytterbium in the Acetate/Amalgam Separation System

The data on the fractionation of all stable isotopes of ytterbium and samarium in a Me(III) acetate/Me amalgam system were obtained. The light isotopes were preferentially fractionated into the amalgam phase. The single separation gains per mass difference were found to be in the range (4.90÷17.8)·10^–4 for ytterbium and (2.2÷3.8)·10^–4 for samarium. The divergence from the linear dependence between separation gains and isotope mass differences was observed and explained as the effect of nuclear field shift and nuclear spin effects. The maximum value of _u.m. was observed to be 17.8·10^–4 for the lightest, neutron deficit isotope of ytterbium, ¹⁶⁸Yb. The same value for the lightest isotope of samarium, ¹⁴⁴Sm, with a magic number of neutrons (82), was close to the mean for other isotopes.     

Ion exchange on resins with temperature-responsive selectivity III. Influence of complex formation stoichiometry on temperature dependence of resin selectivity

The influence of temperature (293308 K 1:1 IDA:Ni2+ complex is dominating. The Cu2+-Ni2+ exchange equilibrium from sulfate medium is characterized by the formation of nickel complexes of both stoichiometries within the whole temperature range studied. The dependence of alpha on T in Zn2+-Co2+ exchange system has been shown to be weaker than that in the Cu2+-Ni2+ system. This result is in a good agreement with the predictions made in the first communication of this series. The results of thermostripping experiments carried out for Cu2+-Co2+ exchange have shown that the efficiency of the thermostripping process depends on both the interval of working temperatures (deltaT) and its position on the temperature scale. The efficiency of thermostripping rises with an absolute deltaT value and also increases following the shift of temperature interval to the lower temperature range.     

Paper chromatography in the separation of ions

Summary A study has been made of the separation of alkali and alkaline earth metals. With mixtures of solvents, such as ethyl cellosolve, water and hydrochloric acid and acetone, water and hydrochloric acid in the ratio of 702010 and at different temperatures, a complete separation of alkaline earth metals was effected. Of the alkali metals only lithium, sodium and potassium could be separated from each other but rubidium and caesium always accompanied potassium.     

Isotopieeffekte bei der Bildung von Natriumkryptaten

The distribution of activity of²²Na⁺ and²⁴Na⁺ in the heterogeneous equilibrium of a cationic exchange resin and the aqueous or methanolic solution was measured in order to evaluate an isotope effect. Using Li⁺-charged ion exchanger in methanol, an enrichment of²⁴Na was observed. If bicyclic aminopolyethers (221, 222) are present in the solution, this effect is not seen. This means that the complexing agents above carry out an enrichment themselves, as could be shown by calculating the corresponding elementary separation factor. The enrichment of²⁴Na on the ion exchanger was measured directly by using Cs⁺-charged exchangers. The analytical method applied is described, and the limits of error are discussed.      

Ion Chromatographic Separation on Silica Grafted with Benzo-18-C-6 Crown Ether

Abstract

Benzo-18-C-6 crown ether has been grafted on silica gel modified with a spacer. By very carefull control of each step of the synthesis an exchanger for alkali and alkaline earth cations with high capacity and low equilibrium time has been prepared. The chromatographic behavior of alkali and alkaline earth metal halides on this benzo-18-C-6 crown ether modified silicas was investigated with water as the mobile phase. With alkali metal chlorides, very good separations are obtained in less than 30 minutes. With alkaline earth metal chlorides, very good separations are also obtained except for Ca²⁺/Mg²⁺. Separations are also observed with mixtures of alkali and alkaline earth cations. Moreover, a very efficient separation of anions is observed, partly as a result of the hydrophobic character of the exchanger.     

Amperometric titration of calcium,strontium and barium and their mixtures in presence of large amounts of alkali metal salts

Trace amounts of alkaline earth metals are titrated with triethylenetetraaminehexaacetic acid; lead(II) is added as indicator and the current is measured by square-wave polarography. At pH 13.3, calcium, strontium and barium give a common end-point corresponding to the total content of alkaline earth ions. Copper and cadmium interfere but small concentrations of Ni, Al, Mg, Zn, Mn(II) and Fe(III) are tolerated. The alkaline earth metals can be determined in the presence of 1000-fold amounts of lithium and 10⁵- fold amounts of sodium or potassium ions.     

Thin-layer chromatographic behavior of rare earths on silica gel with aqueous alkaline earth metal nitrate solutions as mobile phases

The TLC behavior of all the rare earths except Pm has been surveyed on silica gel (pH 7.0) pretreated with 0.1 mol L^–1 tris(hydroxymethyl)aminomethane and 0.1 mol L^–1 HCl with aqueous nitrate solutions of alkaline earth metals as mobile phases. The R_F values of the lanthanides varied in a regular and characteristic way accompanied by the tetrad effect with increasing atomic number, and when the mobile phases were changed the R_F values of each metal decreased in the order Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺, as the crystal ionic radii of the alkaline earth metals increased. This adsorption sequence was not observed with alkali metal nitrate and alkali metal chloride mobile phases. A brief discussion concerning the effect on R_F values of the solvent cations and the adsorption mechanism is included; also presented are typical chromatograms for the separation of multi-component mixtures containing adjacent lanthanides. Received: 9 October 2000 / Revised: 20 February 2001 / Accepted: 26 February 2001     

Fractionation of Sulfur Isotopes in the Course of High-Temperature Roasting of Copper-Nickel Sulfide Ores and Concentrates

The fractionation of sulfur isotopes, namely, enrichment of the cinder with the heavy isotope ³⁴S in the course of roasting of various sulfide ores and concentrates in neutral and oxidative atmospheres at 773-973 K was studied.     

Nuclear field shift effect in isotope fractionation of thallium

Environmental transport of Tl is affected by redox reaction between Tl(I) and Tl(III) and ligand exchange reactions of them. In order to deepen the knowledge of Tl chemistry, we investigated fractionation of Tl stable isotopes (²⁰³Tl and ²⁰⁵Tl) in a chemical exchange system. Tl isotopes were fractionated in a liquid–liquid extraction system, in which aqueous and organic phases are hydrochloric acid solution and dichloroethane including a crown ether, respectively. After purification by ion-exchange chemistry, the isotope ratio of ²⁰⁵Tl/²⁰³Tl in equilibrated aqueous phase was measured precisely by multiple-collector–inductively-coupled-plasma–mass-spectrometry. A large isotope fractionation >1 ‰ was found. Electronic structures of possible Tl species (hydrated Tl⁺, Tl³⁺, and Tl chlorides) were calculated by ab initio methods, and the isotope fractionation factor was theoretically obtained. The isotope fractionation via intramolecular vibrations was calculated to be much smaller than the experimental result. The isotope fractionation via isotopic change in nuclear volume, named the nuclear field shift effect, was calculated to be >1 ‰ in Tl(I)–Tl(III) redox systems and/or ligand exchange systems of Tl(III). The nuclear field shift effect was found to be the major origin of Tl isotope fractionation.     

Temperature dependence of fractionation of hydrogen isotopes in aqueous sodium chloride solutions

The D/H ratios of hydrogen gas in equilibrium with aqueous sodium chloride solutions of 2, 4 and 6 molalities were determined within the range 10 to 95°C, using a hydrophobic platinum catalyst. With each of the different sodium chloride concentrations, the hydrogen isotope effect between the solution and pure water changes linearly with the square of the reciprocal temperature. On the basis of the results for hydrogen isotope fractionation observed in this study, and those of hydrogen isotope fractionation between pure water and vapor, it is concluded that the structure of the aqueous sodium chloride solution does not change significantly with temperature. The hydrogen isotope effect is evidently different from the results of vapor pressure isotope effects (VPIE) on sodium chloride solutions measured on separated isotopes. The difference between the present work and the VPIE studies is probably due to a non-ideal behavior in a mixture of isotopic water molecules and/or to a H₂O-D₂O disproportionation reaction in sodium chloride solutions. The distinction between the latter two mechanisms can not be differentiated at present.     

Carbon isotope fractionation of benzene and toluene by progressive evaporation

Evaporation is one of the key attenuation processes for near‐surface volatile organic compounds (VOCs) in the upper soil zone. Evaporation experiments were performed to investigate the carbon isotope fractionation of benzene and toluene during progressive and non‐equilibrium evaporation at room temperature. Considerable carbon isotope fractionation occurred during evaporative enrichment of benzene and toluene. The carbon isotope compositions of residual compounds increased exponentially with increasing evaporation. Thus, the remaining liquids become isotopically heavier, and the process follows a Rayleigh trend. This result is compatible with the direction of isotopic changes associated with both microbial degradation and volatilization of hydrocarbons previously observed in soil columns, but shows exactly the opposite behavior to previous equilibrium volatilization findings. Copyright © 2010 John Wiley & Sons, Ltd.     

Carbon-13 kinetic isotope effects in the decarbonylations of lactic acid containing13C at the natural abundance level

The¹³C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20–80°C. The¹³C₍₁₎ isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40°C. Below this temperature the¹³C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found inthe decarbonylation of lactic [1-¹⁴C] acid. The experimental values of k(¹²C)/k(¹³C) ratios of isotopic rate constants for¹²C and¹³C are close to, but slightly higher than theoretical¹³C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C₍₁₎-OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H₂O)/(H₂SO₄) ratio caused the increase of the¹³C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5°C to 1.0536±0.0008 (at 80.6°C). A discussion of the abnormally high temperature dependence of¹⁴C and¹³C isotope fractionation in this reaction and the discussion of the problem of relative¹⁴C/¹³C kinetic isotope effects is given.     

Activity ratios of natural uranium in surface waters

The enrichment of²³⁴U in ground waters is a well established experiments fact. In the course of measurements of uranium contamination in rivers of the Guadiana basin we have found the contamination near the uranium mines with the equilibrium isotope ratios of uranium. With distance from the mines we found not only the expected decrease in contamination but also an increasing enrichment of the lighter isotopes. For the²³⁵U isotope, this is the first observation with good separation and low interference between the most significant peaks of each isotope.     

Calciumisotopenseparation und Reaktionsenthalpie. Calciumisotopenseparation und Bestimmung der Reaktionsenthalpie beim Isotopenaustausch an einem stark sauren Kationenaustauscher

Calcium Isotope Separation and Reaction Enthalpy. Calcium Isotope Separation and Determination of Reaction Enthalpy in Ion Exchange Using a Strongly Acidic Cation Exchange Resin In the system of a strongly acidic cation exchanger/BaCl₂ solution the isotope separation between ⁴⁰Ca²⁺ and ⁴⁸Ca²⁺ is investigated using column experiments. ⁴⁸Ca²⁺ is enriched in the solution phase whereas ⁴⁰Ca²⁺ is enriched in the resin phase. A strong dependence of the isotope separation effect on the concentration of the BaCl₂ solution is found. The isotope separation increases with decreasing concentration. The isotope separation also depends on temperature: the isotope separation effect increases with decreasing temperature. A ΔH-value of —5.8 J/mol is determined for the calcium isotope exchange reaction.     

Study of the size-based environmental availability of metals associated to natural organic matter by stable isotope exchange and quadrupole inductively coupled plasma mass spectrometry coupled to asymmetrical flow field flow fractionation

The determination of the isotopically exchangeable fraction of metals in environmental solid samples (soils, composts, sediments, sludges, etc.) is used to know the amount of metal potentially available (E-value). Stable isotopes can be used for determination of E-values through the analysis of the aqueous phases from spiked suspensions. However, the presence of isotopically non-exchangeable metal forms in the aqueous phase led to overestimation of the E-values. In this paper, a method for monitoring the degree of isotopic exchange in function of the molecular mass and/or size of the metal form has been developed based on the direct coupling of asymmetrical flow field flow fractionation (AsFlFFF) with inductively coupled plasma mass spectrometry (ICP-MS) for on-line isotope ratio measurements. ICP-MS data acquisition parameters were stressed to avoid degradation of isotope ratio precision. Two sets of fractionation conditions were selected: a colloids separation, which allowed the separation of substances up to 1 μm, and a macromolecules separation, designed to resolve small size substances up to 50 kDa. The methodology was applied to study the environmental availability of copper and lead in compost samples, where metals are mainly associated to different forms of organic matter. No significant differences on isotopic exchange were observed over the size range studied, validating the E-values determined by direct analysis of the aqueous phases.     

Precise and accurate compound-specific carbon and nitrogen isotope analysis of RDX by GC-IRMS

A new analytical method is presented for the compound-specific carbon and nitrogen isotope ratio analysis of a thermo-labile nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by gas chromatograph coupled to an isotope ratio mass spectrometer (GC-IRMS). Two main approaches were used to minimise thermal decomposition of the compound during gas chromatographic separation: programmed temperature vaporisation (PTV) as an injection technique and a high-temperature ramp rate during the GC run. δ¹⁵N and δ¹³C values of RDX measured by GC-IRMS and elemental analyser (EA)-IRMS were in good agreement within a standard deviation of 0.3‰ and 0.4‰ for nitrogen and carbon, respectively. Application of the method for the isotope analysis of RDX during alkaline hydrolysis at 50°C revealed isotope fractionation factors ε _carbon?=??7.8‰ and ε _nitrogen?=??5.3‰.     

Evaluation of column temperature as a means to alter selectivity in the cation exchange separation of alkali metals, alkaline earth metals and amines

The merits of varying column temperature in a cation exchange separation of alkali metals, alkaline earth metals and amines are considered. Increasing the column temperature (up to 60 degrees C) reduced the retention of all cations, but by varying extents. Consequently, selectivity changes were seen, with reversals in elution order in some cases. To ascertain when temperature is most useful as a separation aid, analytes were classed into three groups according to their temperature behaviour: alkali metals; alkaline earth metals; and amines. Adjusting the column temperature caused selectivity changes between analytes in different groups, but no selectivity changes occurred between analytes in the same group. Further, temperature was compared to the addition of modest amounts of acetonitrile as another means to alter selectivity. The benefits of elevated temperature were not just limited to selectivity changes. Improvements in the efficiencies of all analytes were noted at 60 degrees C. This was especially true for the amines which are severely tailed at ambient temperatures.     

Isotope exchange between alkaline earth metal hydroxide and HTO water in the equilibrium state

In order to reveal to what extent tritium (³H or T) can be incorporated into hydroxides, the isotope exchange reaction (OT-for-OH exchange reaction) between each alkaline earth metal hydroxide (M(OH)₂), where M means alkaline earth metal (M=Ca, Sr or Ba) and HTO water was observed homogeneously at 30 °C under equilibrium after mixing. Consequently, the followings were obtained: (1) a quantitative relation between the electronegativity of each M ion and the ability (of the M ion) incorporating OT^– into the M hydroxide can be found and the ability is small when the temperature is high, (2) the exchange rate for the OT-for-OH exchange reaction is small when the electronegativity of the M ion in the M hydroxide in great, (3) as for the dissociation of HTO water, it seems that fomula (HTOT⁺+OH^–) is more predominant than the fomula (HTOH⁺+OT^–) when the temperature is high and (4) the method used in this work is useful to estimate the reactivity of a certain alkaline material.     

Thin-layer chromatographic behavior and separation of alkaline earth metals on silica gel in aqueous sodium perchlorate solution

The thin-layer chromatographic behavior of alkaline earth metal ions (Mg2+, Ca2+, Sr2+, and Ba2+) in aqueous sodium perchlorate solutions on silica gel thin-layers impregnated with sodium hydroxide has been surveyed as a function of salt concentration. At salt concentrations above 2 mol 1(-1), the selectivity of the metals increased with a decrease in the crystal ionic radii; with further increases in salt concentration, the selectivity differences among the metals expanded remarkably. In the present systems, it was supposed that the cation exchange, the surface complexation, and the salting-out effect participate simultaneously in the adsorption of the metals on silica gel. Typical chromatograms for the mutual separation of the alkaline earth metals are presented.     

Isolation and ion exchanging behaviour of mendelevium/II/

Mendelevium-256 was obtained by irradiating of Bk-249 with Ne-22 ions in the external beam of U-300 cyclotron. An efficient ionexchanging method of medelevium isolation and separation from nuclear reaction products have been developed in which a column with cation exchanger and zinc amalgam and 1M HCl solutions as eluents were used. Under these conditions mendelevium has been shown to be reduced and washed out as an alkaline earth element. The ionic radius of Md²⁺ has been estimated from a correlation of the elution peak positions with ionic radius of several divalent elements. This value was used to calculate the heat of hydration of Md²⁺ ion.