Isotope Enrichment Using Chemical

The Synthesis of Deuterium Derivatives 1.5.7.2. by isotopic Enrichment Using Chemical Reactions... 

Formation of Bonds between Hydrogen and C, Si, Ge, Sn, Pb 123 1.6.7. The Synthesis of Deuterium Derivatives 1.6.7.2. by Isotopic Enrichment Using Chemical Reactions... 

Because of the very large enrichments required in heavy water production, cascades taper markedly. In the upper stages the relative advantage of chemical exchange over water distillation vanishes. Most heavy water plants carry out the last portion of the enrichment by distillation (from 20% or 30% D to 99.85%). Accordingly both exchange and distillation will be briefly treated below. First, however, to clarify the important distinction between chemical and thermal reflux we treat an example of isotope separation using chemical reflux. 

Various borate esters are chemostetilants for house flies (51). Tributyl borate, available from Eagle-Picher, Miami, Oklahoma, which is isotopically enriched in boron-10, is being used as a chemical precursor in the synthesis of pharmacologically active boron compounds suitable for boron neutron capture therapy. 

In 1971, Walcher [326] succeeded in observing a resonance effect of about 0.6% in as a function of the Doppler velocity using a TI2O3 source and an enriched (81% ° Hg) HgO absorber at 4.2 K. The half-width turned out to be Fexp = 76 (10) mm s corresponding to a lower limit of the half-life of fi/2 > 0.1 ns. It is clear that the properties of the ° Hg Mossbauer isotope do not render it an interesting isotope from a chemical point of view. 

Solid-phase peptide synthesis offers a fast and convenient route for many peptides when isotope-enriched compounds are not required. Classical synthesis additionally permits the use of non-natural amino acids and allows site-specific isotope labeling. Although Fmoc protected 15N-labeled amino adds are commercially available, the cost of such synthesis is usually prohibitive, and the peptides from chemical synthesis require perdeuterated detergents and unfortunately exclude investigation of internal dynamics through measurement of 15N relaxation. 

Availability of a sample isotopically enriched with 15N and 13C offers the NMR spectro-scopist additional tools for overcoming the problems encountered in homonuclear experiments. In an obvious extension of the homonuclear experiments, the carbon or nitrogen dimension can be used to improve the resolution in NOESY spectra. However, recent trends clearly favor the through-bond approach where the presence of a cross peak unambiguously proves the existence of a chemical bond between the nuclei involved. Let us review briefly the experiments available for labeled oligonucleotides. 

Deep state experiments measure carrier capture or emission rates, processes that are not sensitive to the microscopic structure (such as chemical composition, symmetry, or spin) of the defect. Therefore, the various techniques for analysis of deep states can at best only show a correlation with a particular impurity when used in conjunction with doping experiments. A definitive, unambiguous assignment is impossible without the aid of other experiments, such as high-resolution absorption or luminescence spectroscopy, or electron paramagnetic resonance (EPR). Unfortunately, these techniques are usually inapplicable to most deep levels. However, when absorption or luminescence lines are detectable and sharp, the symmetry of a defect can be deduced from Zeeman or stress experiments (see, for example, Ozeki et al. 1979b). In certain cases the energy of a transition is sensitive to the isotopic mass of an impurity, and use of isotopically enriched dopants can yield a positive chemical identification of a level. 

Since the level of tritium in the atmosphere is presently greater than 10 TU, it is possible to study many physical and chemical processes using this equipment for sample analysis. Since isotopic enrichment is unnecessary for most samples, direct rapid analysis is possible. The equipment is being used presently to analyze water samples from Nevada in a hydrology project. Table IV shows the analytic data. No attempt has yet been made to evaluate these data. What is apparent qualitatively... 

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