Isotope Exchange Method Research Articles

Surface area of cesium perchlorate

Specific surface area of cesium perchlorate has been determined by isotopic surface exchange, air-permeability, and microscopic methods. There is agreement between the values of specific surface area evaluated by air-permeability and microscopic methods. The results obtained by the isotopic surface exchange method are reproducible but are significantly greater than those obtained by the other methods, and the difference is attributed to the fact that while air-permeability and microscopic methods measure the external surface area, the surface exchange method measures the total surface area (external as well as internal) of solids.

Water diffusion and water permeation in eggs from three Anuran species.

AbstractWater exchange has been studied in ovarian and body cavity eggs of three Anuran species (Rana esculenta, R. pipiens and R. temporaria) with the isotope exchange method using the automatically recording diver balance. In order to estimate the rate of water diffusion in egg cytoplasm (D), a factor required to determine the rate of water permeation (= the exchange coefficient, E), three different chemical treatments (digitonin, ethanol and formaldehyde) have been used to remove the surface barrier to water flow. The obtained mean value of D, 5 × 10−6 cm2 sec−1, has been accepted as a close approximation of water diffusion in the egg cytoplasm. This value has been used to determine the exchange coefficients in the egg types of the above mentioned species. Comparisons have been made between the calculated values of E both within and between species, and some suggestions have been made concerning the influence of microvilli on the rate of water exchange. Although, on the average, water exchange proceeds at a greater rate in ovarian than in body cavity eggs, a measurable diffusion barrier at the surface can be demonstrated.

The porous structure of self-supporting pressed silica discs: I. Infrared spectroscopic studies

Infrared Spectroscopic studies of a range of silicas prepared from an Aerosil show that the 3650-cm −1 absorption band present in the spectrum of silica gels corresponds to the regions of interparticle contact within the gel matrix. A comparison of the spectra of powder silicas and the corresponding self-supporting pressed discs suggests that the latter possesses a microporous gel structure. The reactions of the silicas with heavy water and boron trichloride vapor show that it is not possible to differentiate at all accurately between bulk or internal hydroxyls and surface hydroxyls in silica gel structures by hydrogen/deuterium isotopic exchange methods using heavy-water vapor as the exchanging agent.

Investigation of the content of hydroxyl groups on the surface and in the volume of particles of aerosils (by the method of deutero-exchange)

1. The concentration of hydroxyl groupsαOH on the surface of seven samples of aerosils possessing different values of the specific surfaces, as a function of the temperature of treatment under vacuum, was measured by the method of isotopic exchange with D2O. 2. The values ofαOH at a definite temperature of vacuum treatment of aerosils are close, regardless of their specific surface. In the maximally hydroxylated state, they are an average of ∼7.8μ moles of OH/m2 or 4.7 OH groups/100 A2. The decrease inαOH when the aerosils are heated under vacuum occurs rapidly (by approximately half in the interval from 200 to 400°), while above 400° it slows down, which is due to the different nature of the predominant processes of dehydroxylation of the surface. The hydroxyl groups are found only on the surface of the investigated aerosils.

Study on the Behavior of Sulfur between H25 and ZnS by an Isotopic Exchange Method

焼成雰囲気に35S-硫化水素を用い,同位体交換法により,硫化亜鉛ケイ光体生成過程における固一気相間のイオウの挙動を追跡し,焼成雰囲気の作用機構を検討した。静置式ガス反応装置を用い,硫化亜鉛粉末試料0.59を300～ll50℃,硫化水素1atm下で焼成したのち,気相(硫化水素),固相(硫化亜鉛)および反応管冷却部に沈着する遊離イオウの各比放射能を測定し,これら各物質間のイオウの移行量を算出した。その結果,固-気相間の同位体交換反応はかなり容易に進行し,固相に移行したイオウは500℃ 以上でその内部に均一に分布すること,またその交換量は500～8000℃ 近辺で極大値を示すことなどを見いだした。遊離イオウの沈着量は気相からよりも固相からの方が圧倒的に多量であることを示した。また,示差熱テンピンにより硫化亜鉛の熱分解を調査した結果,500℃ 以下ではおもにイオウが蒸発し,それ以上で亜鉛の蒸発が起こり,さらに1050℃ 以上で硫化亜鉛の昇華も認められた。これらの結果から,焼成過程における硫化亜鉛粒子の焼結および相転移にともなう格子欠陥の発生と交換反応との関係を検討し,焼成雰囲気の作用機構を考察した。

Studies on the mechanism of methanolysis of some methyl D-glycopyranosides by the method of isotope exchange

Methyl α- and β- D-hexopyranosides, as well as methyl 2,3,4,6-tetra- O-acetyl-α- and -β- D-glucopyranosides and the D-galactose and D-mannose analogues, were heated in 14C-labelled methanol containing 1% of hydrogen chloride. Exchange of the methoxyl group occurred under these conditions; the acetates were also deacetylated. According to chromatographic analysis and the extent of isotope exchange, the glycosides investigated were divided into two groups. The first group included methyl α- D-glucopyranoside and methyl α- D-mannopyranoside, for which exchange proceeds probably by way of a cyclic carbonium ion. The second group includes methyl β- D-glucopyranoside, methyl α- and β- D-galactopyranosides, and methyl β- D-mannopyranoside, for which the exchange mechanism probably involves an acyclic ion.

Applicability of an Isotope Exchange Method for the Determination of Milligram and Microgram Quantities of Organic Mercurials. I. Pharmaceutical and Agricultural Mercurials

Abstract The isotope exchange technique was applied to the analysis of milligram and microgram quantities of organic mercurials, with emphasis on pharmaceuticals and fungicides of an agricultural nature. Average recovery was 98.48 ± 1.12% for Hg-203 in equilibrium with chemical mercury. In comparison studies, the isotope exchange procedure showed essential agreement with standard techniques for mercury determination. At low levels, traces of mercury via glassware contamination were observed to interfere. The digestion system was found to be applicable to most organic mercurials studied except ethyl mercuric phosphate and three commercial fungicides.

Anion Diffusion in Crystals of NaCl

Diffusion coefficients of the chloride ion in NaCl have been measured between 300° and 700°C using an isotopic exchange method. The concentrations of cation impurities were deduced from electrical conductivity measurements over the same temperature range. In the extrinsic region, the diffusion coefficients do not decrease with increasing amounts of cation impurity to the extent required for diffusion by single vacancies. The general conclusion that diffusion occurs both by single vacancies and by vacancy pairs agrees with that reached earlier by Laurance. Analyses of the experimental results in the intrinsic region yield for single vacancy anion diffusion Da=1.1×e−1.92/kT cm2 sec−1 and for vacancy pair diffusion Dp=363×e−2.37/kT cm2 sec−1, and the activation energies, which are given in electron volts, agree well with theoretical estimates. Large variations were observed in the anion diffusion coefficients for crystals doped with Ca++; the cause cannot be established definitely.

A determinação da capacidade de troca de cátions do solo e de argilas por meio da troca isotópica com cálcio radioativo

O presente trabalho descreve a determinação da capacidade de troca de cátions (CTC) do solo e de argilas, através da troca isotópica com cálcio radioativo, 20Ca45. Foi determinada a CTC de oito amostras de solo e de quatro de argilas, tendo sido feitas 5 pesagens de cada amostra de cada um dos materiais, a fim de se avaliar a precisão do método. O cálculo da CTC foi feito mediante a expressão: X = a1/a2 c - c a1 = atividade específica do cálcio da solução de equilíbrio antes de entrar em contato com o solo. a2 = atividade específica do cálcio da solução de equilíbrio após o contato com o solo. c = número de e.mg de cálcio da solução de equilíbrio e calculado para 100g de solo. X = capacidade de troca de cations em e.mg por 100g de solo.

On the rate of water exchange across the surface of animal cells

The two methods for determination of water permeability, the osmometric method, and the isotope exchange method are discussed, particularly with respect to the sources of error. In the latter method the exchange across the surface barrier is generally so fast that correction for the diffusion in the cytoplasm is required. The presence of cortical layers of considerable mechanical strength may often invalidate results obtained with the former method. In agreement with views advanced previously in the literature, it is concluded that the permeability coefficients obtained by the two different methods only under very special conditions are identical. However, the ratio cannot be expected to deviate much from unity, and it is shown that the large ratios reported in some cases do not represent the ratio between two permeability coefficients.

A study of reactions of electrophillic substitution at a saturated carbon atom by the method of isotopic exchange

1. The kinetics of the isotopic exchange in pyridine solution between the ethyl ester of α-bromomercuryphenylacetic acid and Hg* Br2 at 50, 60, 70 and 80° were studied. 2. The reaction is bimolecular-first order for each component. The parameters of the Arrhenius equation were determined.

A study of reactions of electrophillic substitution at a saturated carbon atom by the method of isotopic exchange

A study of reactions of electrophillic substitution at a saturated carbon atom by the method of isotopic exchange

Separation of Radioactive Zinc from Reactor Cooling Water by an Isotope Exchange Method

A method was developed to separate radioactive zinc from reactor cooling water by isotope exchange with inert zinc in the form of zinc amalgam. The radioactive zinc was recovered in high yield and free from all other activities except Cu/sup 64/and traces of Mn/sup 56/ by a single contact with zinc amalgam. The Cu/sup 64/ interference could be removed quantitatively by a pre-extraction into cadmium amalgam. The procedure is rapid and simple enough to warrant application to an automatic analyzer for continuous measurement of radioactive zinc in waste streams. (auth)

The use of radioactive isotopes for determining saturated vapour pressure

A brief survey is given of methods, techniques and experimental arrangements for measuring vapour pressure using radioactive isotopes. Determination of the vapour pressure by a static method from a direct measurement of the radioactivity of the vapour with a counter, from the activity determined by a photographic method or by radio-chemical methods, is described. Papers concerned with the measurement of the vapour pressure by the boiling point and the jet-method are discussed. The variations in Langmuir's method depending on the evaporation of material from a filament and from a crucible are analysed. The vapour pressure of liquid metals and liquid alloy components is calculated from the activity of the condensate. A variation of the method is described in which the vapour pressure is determined from the radioactivity of part of the condensate. The integral and differential variations (integral with collection of all the vapour and differential with collection only of part of the vapour phase) of Knudsen's method are discussed, together with results of vapour pressure measurements of elements and alloy components by radiometric analysis of the condensate. The last section describes measurements of vapour pressure by the isotope exchange method. A table is given showing the comparative sensitivity of the different methods of measuring vapour pressure.

Investigation of electrophilic and homolytic substitutions at a carbon atom by the method of isotopic exchange

1. Diarylmercurys and arylmercury chlorides undergo isotopic exchange with mercury labeled with Hg under very mild conditions. Electropositive substituents in the para position of the benzene ring facilitate reaction, and electronegative substituents make it more difficult. 2. The homolytic reactions examined are not free-radical reactions, but proceed directly between organo-mercury molecules and mercury. 3. A study was made of the dependence of the rates of isotopic exchange of acyclic and alicyclic organo-mercury salts with mercury and with mercury chloride on structural factors and on additions of acids and bases. 4. The homolytic (with\(\mathop {Hg}\limits^* \))and electrophilic (with\(\mathop {HgX_2 }\limits^* \)) isotopic-exchange reactions of organomercury salts proceed with preservation of the configuration at the saturated carbon atom. 5. By study of the isotopic exchange of 2-chlorovinylmercury compounds with\(\mathop {Hg}\limits^* \) and\(\mathop {HgCl_2 }\limits^* \), direct proof was obtained of the correctness of Nesmeianov and Borisov's rule concerning the preservation of stereochemical configuration in electrophilic and homolytic substitutions at an olefinic carbon atom.

Spectral-isotopic method for the determination of hydrogen in metals

An isotopic exchange method of hydrogen determination is presented in which the hydrogen in the metal sample is allowed to come to equilibrium with deuterium introduced to the systems the isotopic composition of the gas is then determined by spectroscopic analysis. (J.R.D.)

The use of radioactive isotopes for determination of saturated vapor pressure

A short survey of methods and apparatus arrangements used for measurement of vapor pressure by means of radioactive isotopes is given here. A description is given of vapor pressure determination by the static method, through the direct measurement of radioactivity in the vapor by a counter, or through the determination of activity by radiographic and chemical means. Work on measurement of vapor pressure along the lines of the boiling point method and the jet method, is presented. On the basis of two works, the method of Langmuir in the variant of vaporization of matter from a thin wire and vaporization from a crucible, is discussed. The vapor ressure of liquid metals and of components of liquid alloys is derived from the activity of the condensate. A variation of this method is described, in which the vapor pressure is determined from the activity of part of the condensate. Integral (with collection of all vapor), and differential (with collection of only part of the vapor phase) variations of Knudsen's method are presented, as well as the results of measurement of vapor pressure of elements and components of alloys by means of radiometric analysis of ccndensate. In the last section a description is given of measurements of vapor pressure by the method of isotope exchange.

Preparation of Tritium-labelled Derivatives of Benzoic Acid

ISOTOPE exchange methods have long been employed for the study of the reactions of hydrogen atoms attached to aromatic ring-systems, and also, to a limited extent, for preparative purposes1,2. Most of the preparations described in the literature were carried out with water of a comparatively low deuterium content. While these methods are not suitable for the preparation of compounds having a high D : H ratio in the labelled groups, they are (apart from questions of economy in the use of tritium), in principle applicable to the preparation of tritium-labelled materials, since the tritium content of the starting material (water) is normally much less than 1 per cent. The present communication describes a simple, rapid and direct method for the labelling of p-nitro benzoic acid at very high specific activity, with considerable economy in the use of radioactive material. It is also suitable for use with deuterium at high abundance. The two isotopes can, with advantage, be combined in the same preparation: analytical procedures (for example, infra-red spectroscopy) are thereby considerably facilitated.

Isotopic exchanges and the existence of tricalcium phosphate in bone.

THE problem of the physico-chemical constitution of the skeleton has received considerable attention in recent years1–3. Tracer experiments indicate that phosphorus-32 and calcium-45 appear promptly and in considerable proportions in the bony tissues, whence they are removed slowly4–6. These observations have led to an assumption that deposition of phosphorus-32 and calcium-45 in bony tissues is an exchange between bone and blood inorganic phosphate or calcium. Phosphorus-32 and calcium-45 have been used to study phosphate or calcium exchange between powdered bone and aqueous disodium hydrogen phosphate and calcium chloride solutions7–9. Different authors8,10,11 have concluded that the principal bone component is not tricalcium phosphate but rather hydroxylapatite to which phosphoric ions are adsorbed in such a quantity that the ratio of calcium to phosphorus is equal to 1 .94, which is the characteristic value for tricalcium phosphate. On the other hand, the findings of some workers1,2 support the idea of the existence of tricalcium phosphate in bony tissues. The experiments reported here are an attempt to study the exchange mechanism of both phosphate and calcium between pure tricalcium phosphate and radioactive phosphate or calcium solutions. These experiments were also performed in order to show to what extent the isotopic exchange method can help to elucidate a particular problem of structural chemistry. (Calcium-45 was prepared by neutron bombardment in the pile at the Clinton Laboratories, Oak Ridge, Terin., and phosphorus-32 at the pile at Harwell, Berks.)