Isotopic correction

Figure 4. Graphical representation of detrital-isotope correction for °Th/U dating. Apparent ages (in parentheses) age shown for both the measured and detritus-corrected isotope ratios.

Slope of regression line yields the initial-isotope corrected for the age equation (Eqn. 2). 

VanVleck JH (1936) On the isotope corrections inmolecular spectra. J Chem Phys 4 327-338... 

A variety of different fitting procedures were used in an attempt to determine from the experimental data. Whatever the fitting proceedure used it was difficult to obtain good fits to the data with constrained to the value determined by the deuterium atom experiments. Unconstrained fits return a value of 4.68 x 10 ° cm molecule s for Ajh using the master equation techniques outlined in the previous section. One is left with the conclusion that either the experimental data are in error or some aspect of the modelling procedure, either the isotopic correction or the extrapolation is at fault. Independent evidence for the validity of the CH3 + H data and extrapolation comes from a calculation by Quack and Troe [67] who calculated a value of 4.7 x lO cm molecule s for k - However, more detailed ab initio calculations [68] predict Ajd close to the experimental values and with a V2 isotope dependence. The two sections of experimental evidence would therefore seem to be incompatible unless there is an anomalous isotope effect. Further work, both experimental and theoretical, is required as the reaction is of considerable significance in combustion. 

B. Fry, S.R. Silva, C. Kendall, R.K. Anderson (2002) Oxygen isotope corrections for online 6 S analysis. Rapid Comm. Mass Spectrom. 16, 854-858... 

Liebisch G, Lieser B, Rathenberg J, et al. (2004) High-throughput quantification of phosphatidylcholine and sphingomyelin by electrospray ionization tandem mass spectrometry coupled with isotope correction algorithm. Biochim Biophys Acta 1686 108-117... 

Figure 8. Xenon isotopes corrected for atmosphere contributions measured in uraninite and pitchblendes plotted after Eikenberg et al. (1993). Xe isotopes are dominated by production from the spontaneous fission of (Xe( Usf)). In these massive samples only, Xe from thermal neutron induced fission of (Xe( Unf-thermai)) is also resolvable. Xe fission products from fast neutron interactions with (Xe( Unf.fast)) are negligible.

Considerable ambiguity can and does arise in the application of isotopic correction. No confusion can arise if either the raw data are presented or a clear statement is made of the isotopic corrections applied. Regretfully, such practice is far from universal in the literature. The charge-... 

Eibl, G., Bernardo, K., Koal, T., Ramsay, S.L., Weinberger, K.M. and Graber, A. (2008) Isotope correction of mass spectrometry profiles. Rapid Commun. Mass Spectrom. 22, 2248-2252. 

Zj has previously been called the type I isotope correction factor [22] n and s are the numbers of total carbon atoms in the species of interest and the selected internal standard, respectively / and are the monoisotopic peak intensities of the species and the internal standard, respectively c and are the concentration of the species of interest and the internal standard, respectively. The dots represent the contribution of other isotopologues which contain more than two atoms. These terms can be ignored in most cases without affecting the accuracy of quantification. 

Ki = isotopic correction factor (see Table 1), and K2 = mole sensitivity for n (see Table 1). 

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