Isotope analyses deuterium

As vanilla, as a result of its high price, is often adulterated or diluted, a number of publications deal with the detection of piperonal, coumarin, ethyl vanillin, vanitrop and others. Whereas these adulterations can be detected rather easily, the addition of synthetic vanillin, as long as it remains within certain proportions, can only be certified by the expensive isotope analysis (deuterium, C content) [296, 297, 298, 299[. 

Lei HW, Suh S, Gurau B, Workie B, Liu R, Smotkin ES. 2002. Deuterium isotope analysis of methanol oxidation on mixed metal anode catalysts. Electrochim Acta 47 2913-2919. 

From the isotopic decomposition of normal H one finds that the mass-2 isotope, 2H, or D (for deuterium) as it is also written, is relatively rare. On Earth it constitutes only 0.015% °f all H isotopes. This makes it 6670 times less abundant than 1H. This information comes from the isotopic analysis of sea water however, deuterium is even more rare in the universe Modern observations of the interstellar gas reveal it to be ten times less abundant relative to H than it is in sea water. This makes the deuterium abundance of Earth the first great isotopic anomaly namely, that D in sea water has been enriched tenfold by the historical processes by which the Earth s oceans were formed from the initial interstellar matter from which the solar system was built. 

C. Guillou, G. Remaud, G.J. Martin (1991) Application of deuterium NMR and isotopic analysis... 

Over the years, Site-Specific Natural Isotope Fractionation (SNIF) NMR has been used extensively in food analysis. Deuterium ( H) is widely dispersed in the whole solar system and so it is as well on earth. Actually, the deuterium isotope ratio in water, usually expressed in parts per milhon (ppm - just... 

Compston W, Epstein S (1958) A method for the preparation of carbon dioxide from water vapor for oxygen isotopic analysis. EOS Trans Am Geophys Union 39 511 Craig H, Horn B (1968) Relationships of deuterium, oxygen-18, and chlorinity in the formation of sea ice. EOS Trans Am Geophys Union 216... 

A quite different use of isotopes in mechanistic studies involves their use as labels for ascertaining the location of a given atom involved in a reaction. As in kinetic experiments, the isotopic substitution will not qualitatively affect the course of the reaction. The nuclei most commonly used for isotopic tracer experiments in organic chemistry are deuterium, tritium, and the and isotopes of carbon. There are several means of locating isotopic labels. Deuterium can frequently be located by analysis of NMR spectra. In contrast to the normal isotope, deuterium... 

The difference in the adsorption isotherms of isotopic molecules has long been known and it has been used for isotope separation and isotope analysis. For example, deuterium gas exhibits an enrichment factor of 40 ( ) at 20 K on silica gel, but the enrichment factor decreases steeply with increasing temperature (Krumbiegel 1970). Another example is the behavior of CH4/CD4 system in a capillary column with activated glass surface at 153 K the retention time of CH4 is larger than that of CD4, at 130 K they are equal to each other and at lower temperatures CH4 leaves earlier the column than CD4 (Bruner et al. 1966). Similarly to the gas-solid chromatographic separations, gas-liquid separation techniques have also been widely used for isotopic separation and for rapid and convenient analysis of mixtures of... 

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

Raman Spectroscopy. Raman spectroscopy is an excellent method for the analysis of deuterium containing mixtures, particularly for any of the diatomic H—D—T molecules. For these, it is possible to predict absolute light scattering intensities for the rotational Raman lines. Hence, absolute analyses are possible, at least in principle. The scattering intensities for the diatomic hydrogen isotope species is comparable to that of dinitrogen, N2, and thus easily observed. 

It has been reported that exchange of protons activated by enolization can be performed directly in a glass inlet system of the mass spectrometer prior to analysis by heating the sample at about 200° with deuterium oxide vapor for a few minutes. " Exchange has been observed with 2-, 3-, 6-, 11- and 17-keto steroids, but the resulting isotopic purity is usually poor,... 

Reductive opening of the cyclopropyl ring in 9j5,19-cycloandrostan-ll-one (234) has been achieved by treatment with a large excess of sodium in iso-propanol-OD. Analysis of the product for isotopic purity after oxidation to the corresponding ketone and base-catalyzed back exchange of the 9a-deuterium [(235) (236)] shows 19% do and 10% 62 isotopic impurities. The 10% 62 product is probably due to incomplete back exchange. 

His researches and those of his pupils led to his formulation in the twenties of the concept of active catalytic centers and the heterogeneity of catalytic and adsorptive surfaces. His catalytic studies were supplemented by researches carried out simultaneously on kinetics of homogeneous gas reactions and photochemistry. The thirties saw Hugh Taylor utilizing more and more of the techniques developed by physicists. Thermal conductivity for ortho-para hydrogen analysis resulted in his use of these species for surface characterization. The discovery of deuterium prompted him to set up production of this isotope by electrolysis on a large scale of several cubic centimeters. This gave him and others a supply of this valuable tracer for catalytic studies. For analysis he invoked not only thermal conductivity, but infrared spectroscopy and mass spectrometry. To ex-... 

Since spillover phenomena have been most directly sensed through the use of IR in OH-OD exchange [10] (in addition, in the case of reactions of solids, to phase modification), we used this technique to correlate with the catalytic results. One of the expected results of the action of Hjp is the enhancement of the number of Bronsted sites. FTIR analysis of adsorbed pyridine was then used to determine the relative amounts of the various kinds of acidic sites present. Isotopic exchange (OH-OD) experiments, followed by FTIR measurements, were used to obtain direct evidence of the spillover phenomena. This technique has already been successfully used for this purpose in other systems like Pt mixed or supported on silica, alumina or zeolites [10]. Conner et al. [11] and Roland et al. [12], employed FTIR to follow the deuterium spillover in systems where the source and the acceptor of Hjp were physically distinct phases, separated by a distance of several millimeters. In both cases, a gradient of deuterium concentration as a function of the distance to the source was observed and the zone where deuterium was detected extended with time. If spillover phenomena had not been involved, a gradientless exchange should have been observed. 

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