Compounds isotopes

Target compound Isotope Enrichment factor References... 

Parent compound Isotopic species Spectroscopy Structural information Reference... 

Therefore, this chapter provides a summarized data on the preparation of organic ion-radicals as independent particles that can be free or bound with counterions in ion pairs. The chapter considers liquid-phase equilibria in electron transfer reactions and compares electrode and liquid-phase processes for the same organic compounds. Isotope-containing molecules have specific features as ion-radical precursors, therefore, the generation of the corresponding ion-radicals is considered in Section 2.6 of this chapter. This chapter also pays some attention to the peculiarities of ion-radical formation in living organisms. 

Schmidt H-L, Eisenreich W (2001) Systematic and regularities in the origin of patterns in natural compounds. Isotopes Environ Health Stud 37 253... 

Additionally, mass spectrometry methods have been successfully applied for the identification of other Zn-containing complexes. Among them are compounds containing two Zn atoms (30-32), as well as some complexes that exist as dimers in the condensed phase according to different physical methods " (33-42). For all these compounds, isotope clusters with isotopic distributions similar to the graphical representations in Figure lb (for [Zni] ) were expected, provided that the binuclear species or dimer entities are able to survive the ionization process. 

In the determination of the sequence of intermediates of a specific pathway, one single probe, the use of isotopically labelled precursors, has proven of pivotal importance. With the appropriate safeguards, which we shall consider below, the administration of a compound isotopically labelled in a recognizable pattern and the subsequent isolation of a labelled metabolite in which the distribution of label can be recognized as occurring without randomization constitutes de facto evidence of a precursorial relationship. 

Aroma compound Isotope label for standard Literature references... 

An isotopically labeled compound is a mixture of an isotopically unmodified compound with an analogous isotopically substituted compound or compounds. Isotopically labeled compounds may be specifically labeled or selectively labeled. To indicate isotopic labeling, the number and symbol (and locants if needed) are enclosed in square brackets closed up to the compound name or formula. 

DETERMINATION OF UNKNOWN AMOUNTS OF UNLABELED COMPOUNDS—ISOTOPE DILUTION... 

Instead by solvent extraction [207], aroma compounds from aqueous media, e.g. fruit juices, can even be separated and enriched by techniques of solid phase micro extraction (SPME), preferably from the headspace [208] , corresponding devices can often be directly connected to GC systems. These techniques provide the complete spec-tmm of the individual compounds of an aroma. As it will normally not be possible and even not necessary to analyse all components of the complex mixture, the separation of its main compounds may demand a multi-dimensional (MD) gas chromatographic system [209[ as displayed in Fig. 6.14 [210[. Examples for the multi-ele-ment/multi-compound isotope analysis by such systems will be given later (6.2.2.4.4, [211[) they can even integrate the identification of the compounds by molecular mass spectrometry and a simultaneous determination of the enantiomer ratios of isomers [210, 211 [. The importance of enantiomer analysis as a tool for authenticity assessment is extensively treated in chapter 6.2.3. 

Most flavourings are complex mixtures of many compounds. As IRMS makes only sense with pure analytes, a strict purification of individual substances is indispensable. Therefore GC-IRMS has been further developed and optimised to multi-compound isotope ratio analysis by its coupling IRMS to capillary (c) and multidimensional (MD) gas chromatography (see 6.2.2.2.2). This methodology demands a strict intrinsic control and standardisation [340] apart from the international standards (see Table 6.3) also secondary standards like the polyethylene foil IAEA-CH7 or the NBS22 oil are available from the IAEA in Vieima. However, as these substances are also not suitable for the direct standardisation of data from a coupled GC system for flavour isotope analysis, certificated tertiary laboratory standards for hydrogen have been developed by parallel analysis of flavour compounds by TC/EA-IRMS and MDGC-P-IRMS [210]. 

Thallium(i) Compounds.—Isotopic exchange reactions between and Tl have been studied in a variety of solvents (H20-Et0H, H20-glycol, H2O-DMSO). ... 

An understanding of biosynthetically controlled, between-compound isotopic contrasts is required in order to judge whether plausibly related carbon skeletons found in a natural mixture might come from a single source or instead require multiple sources. 

Ishida, K. Matsuo, T. Suga, H. Zielenkiewicz, W. Lipkowski, J. Low temperature properties of the Werner clathrate inclusion compounds. Isotopic p-xylenes in tetrakis (4-methylp3nidine) nickelfll) thiocyanate. J. Chem. Thermodyn. 1998, 30, 1289. 

See also Analytical Reagents Purification. Arsenic. Atomic Absorption Spectrometry Electrotfiermal. Atomic Mass Spectrometry Inductively Coupled Plasma. Dioxins. Elemental Speciation Oven/iew. Endocrine Disrupting Chemicals. Geochemistry Sediment. Humic and Fulvic Compounds. Isotope Dilution Analysis. Mass... 

Reacting atom Type of reaction Compound Isotope effect... 

For measurements of synthesized compounds, isotopic labelling with e.g. C-13 or N-15 can be considered. 

Use an internet search engine (such as http //www.go< e. com) to locate information on volatile uranium compounds. Isotopes of uranium are separated by taking advantage of the principle that gases of different masses diffuse at different rates. What is the volatile uranium compound used in the separation of its isotopes What is yellow cake ... 

The first experimental proof of the mechanism of the silylation in the McKenna reaction has been presented by Blazewska. The reaction of a model compound isotopically enriched diethyl phenylphosphonates (644) (P= 0 or P= 0) showed that reaction in acetonitrile proceeded via an attack of P=0 ojgrgen on the silicon atom in hromotrimethylsilane (Scheme 188). The change in the phosphorus-o g gen hond order was directly detected using P and NMR spectroscopy. 

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