Isotopic homologs

Internal standards can be considered under four major groups isotope, homolog, generic, and chemically unrelated. To some extent the type of internal standard dictates its applicability. 

Molecules and ions of identical elemental conposition but differing in isotopic composition are termed isotopic homologs or simply isotopologs. For example, H3C-CH3 and H3C- CH3 are isotopologs. Molecules and ions of identical isotopic composition but differing in position of the isotopes are termed isotopomers. For example, H2C=CD2 and HDC=CHD are isotopomers. 

The cocktail of isotopically labeled standards is not covering any possible detectable AC. Therefore, for some of them, the internal standard to refer to is not the isotopic homolog but some other compound, very close in terms of structure and mass. For making the measurement free from a significant bias, it is desirable that specific sensitivities displayed by either the analyte or the used internal standard should be as similar as possible. Failing in that, results are significantly biased. 

Study of the chemical properties of element 104 has confirmed that it is indeed homologous to hafnium as demanded by its position in the Periodic Table (20). Chemical studies have been made for element 105, showing some similarity to tantalum (25) no chemical studies have been made for elements 106—109. Such studies are very difficult because the longest-Hved isotope of 104 ( 104) has a half-Hfe of only about 1 min, of 105 ( 105) a half-Hfe of about 40 s, of 106 ( 106) a half-Hfe of about 1 s, and of elements 107—109 half-Hves in the range of milliseconds. 

Irreversible processes are mainly appHed for the separation of heavy stable isotopes, where the separation factors of the more reversible methods, eg, distillation, absorption, or chemical exchange, are so low that the diffusion separation methods become economically more attractive. Although appHcation of these processes is presented in terms of isotope separation, the results are equally vaUd for the description of separation processes for any ideal mixture of very similar constituents such as close-cut petroleum fractions, members of a homologous series of organic compounds, isomeric chemical compounds, or biological materials. 

The alkane series is present in mass spectra of any compound containing an alkyl group. In case of isobaric series (e.g., alkanes and ketones) one should pay attention to the intensities of the isotopic peaks. Thus, for the isobaric ions of m/z 43 (CH3CO and C3H7) the abundance of the isotopic peak (m/z 44 ion) will be 2.2% and 3.3%, respectively. The situation is very simple with A + 2 elements. In this case there are two homologous ion series due to A and A + 2 ions. It is worth emphasizing that... 

Californium is a transuranic element of the actinide series that is homologous with dysprosium (gjDy), just above it in the rare-earth lanthanide series. Cf-245 was the first isotope of californium that was artificially produced. It has a half-life of just 44 minutes. Isotopes of californium are made by subjecting berkelium to high-energy neutrons within nuclear reactors, as follows + (neutrons and A, gamma rays) — °Bk — °Cf + (3- (beta particle... 

Ununpentium is also known as eka-bismuth because it is homologous to the element bismuth located at the bottom of Group 15 (VA). Its melting point, boihng point, and density are unknown as are many of its other properties. Several isotopes of element 115 were produced by the nuclear reaction that bombarded calcium into a target americium, resulting in the fusion of the calcium nuclei with the americium nuclei to form isotopes of element 115 (ununpentium). 

Selected entries from Methods in Enzymology [vol, page(s)] Pepsin Activation energy, 63, 243-245 isotope exchange, 64, 10 kinetic constants, 63, 244 kinin-releasing enzyme, 80, 174 porcine, homology to cathepsin D, 80, 578 spectrokinetic probe,... 

On average, the deviation between the measured and calculated masses was 0.0003 amu. Further support for the assigned formulae comes from the fact that an entire homologous series was observed where the mass of each homolog was measured with high accuracy. In many cases, final confirmation of the assigned molecular formula results from observation of the 34s isotope peak two amu higher at the correct precise... 

The most important advantage of such an IDMS procedure is that it compensates in an ideal way both for losses during sample workup and for variations in mass spectrometric response. As demonstrated by Claeys et al. (1977), the use of a stable isotope-labeled internal standard, as opposed to the use of homologs, produces the lowest variance factors due to instrumental stability and sample manipulating errors. Moreover, IDMS can be used both with and without prior chromatographic separation, as for instance in... 

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