SOTOPIC enrichment of organic compounds in the stable minor isotopes 15N, 17O and 18O, which are often used as tracers, is commonly achieved by syntheses that involve isotopically enriched simple precursors such as NH3, H2O and CO2. But such labelled compounds are not always commercially available or readily synthesized. Here we report the direct enrichment of nitrogen and oxygen isotopes in dissociable compounds such as amines, phenols and carboxylic acids, using a high-performance liquid-chromatography technique. The separation method relies on the isotope effects on the dissociation equilibria of weak acids and bases that occur in protonation or deprotonation of the relevant isotopes. Enrichment of 15N to 5−10% isotopic purity in N,N-dimethylaniline was achieved from the natural abundance of 0.37% in less than 14 hours; subsequent runs brought the isotopic purity to 90% or more. Enrichment of 117O and 18O to similar high purities inp-nitrophenol was also obtained. Thus, where suitable dissociation eqilibria exist, direct isotopic enrichment is possible using standard techniques without the need to devise complex synthetic pathways.
2006-11-29 06:25:58
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answer #1
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answered by blapath 6
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Cool them to a very low temperature. The nitrogen turns to a liquid befor the oxygen.
2006-11-29 14:32:31
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answer #2
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answered by Gene 7
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