Hydrogen isotopes preparation

Gehre, M., Hoefling, R., Kowski, P. and Strauch, G. (1996) Sample preparation device for quantitative hydrogen isotope analysis using chromium metal. Analytical Chemistry 68, 4414 4417. 

Hydrogen-deuterium exchange Preparative separation of hydrogen isotopes. 

Analytical nncertainty for hydrogen isotope measnrements is nsually in the range 0.5 to 5%c depending on different sample materials, preparation techniques and laboratories. 

Stereochemically defined, isotopically prepared methyl groups used to determine the stereochemical course of methyltransferases . One typically utilizes [(S)-or [(i )- H,2H,iH]CH3X where X is the remaining part of the substrate. This process cannot be observed when all three hydrogen atoms are H, because they are equivalent and stereochemically indistinguishable. 

Among the classic methods for the extension of the aldose chain by one carbon atom from the reducing end [9J, the Kiliani-Fischer cyanohydrin synthesis [10] is a milestone in carbohydrate chemistry. However after 110 years from discovery and numerous applications [11], including the preparation of carbon and hydrogen isotopically labeled compounds for mechanistic and structural studies [12], there are still several drawbacks that make the method impractical. These are the low and variable degree of selectivity and the harsh reaction conditions that are required to reveal the aldose from either the aldonic acid or directly from the cyanohydrin. Synthetic applications that have appeared in recent times confirmed these limitations. For instance, a quite low selectivity was registered [13] in the addition of the cyanide ion to the D-ga/acfo-hexodialdo-l,5-pyranose derivative 1... 

Hydrogen isotope exchange reactions have long been used to prepare deuterated organic compounds (Miklukhin, 1961). The extension of the range of substances which can take part in hydrogen exchange reactions, which has been the result of the use of liquid deuterio-ammonia as the reactive medium, has opened new possibilities as far as such preparations are concerned (Shatenshtein and Izrailevich, 1957 Bardasova et al., 1960). 

Fig. 3. (a) Schematic of the thin film target for the d/xt formation measurements consisting of the emission, the moderation and the reaction layers, which are prepared by rapidly freezing hydrogen isotopes on the gold foils (not shown) held in vacuum at 3.5 K. [13] The layer thickness (3.43 mg-cm-2, 96 pg-cm-2, and 21 pg-cm-2, respectively) were measured off-line via a particle energy loss (see Fig. 5) (b) Measured Si energy spectra with prompt (I t > 0.02 ps) and delayed (II t > 1.5 ps) time cuts. Fusion in DS reaction layer is separated from that in US D2 due to the pf TOF across the vacuum... 

This technique played a big role in the synthesis of all possible isomeric forms of lactic acid in which the methyl contains all three hydrogen isotopes and the hydrogen at C-2 can be either H, 2H or 3H. Each of the three structures, CH3CHOHCOOH, CH3C2HOHCOOH and CH3C3HOHCOOH, contains two chiral centers when the methyl is CH2H3H. Each structure thus exists in four forms, for a total of 12 isomers. They can all be prepared in substantial amounts and with high optical purity [133]. 

Table 6.12 Site-specific stable hydrogen isotope ratios ofR(-)-linalool extracted from different botanical sources or prepared from fossil materials. Adapted from [230] with kind permission. Copyright [1992] American Chemical Society. The site-specific D/H-ratios are expressed in parts per million [ppm], position indication see Fig. 6.21...

Use Preparation of finely divided uranium metal by decomposition, separation of hydrogen isotopes, reducing agent, laboratory source of pure hydrogen. 

Cylinders of the flashed gas were analysed for hydrocarbon gas composition on a Carle gas chromatograph (GC) system equipped with both a thermal conductivity detector (TCD) and a flame ionization detector (FID). An offline preparation system and dual inlet mass spectrometer (MS) were used to analyse the carbon and hydrogen isotopic values of hydrocarbon components. A customized Gow Mac GC was interfaced with a vacuum/combustion system to separate hydrocarbons from other components and combust to CO2 and water that were purified and sealed into Pyrex tubes for isotopic analysis. The CO2 was analysed directly on one of three dual inlet mass spectrometers Finnigan Delta S, Finnigan Delta + XL or VG SIRA II. The water was reacted with zinc turnings and converted to hydrogen gas, which was analysed on either the Delta S or Delta + XL MS. 

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