13C isotope

For example, the 13C isotope will contribute approximately 2% to the M + 2 in compounds containing 20 carbon atoms. 

Not long ago this could have been determined only by extremely laborious, and often equivocal, selective degradation experiments but the coming of carbon n.m.r. spectroscopy has now made all the difference. Neither the 12C nor the 14C carbon isotopes produce an n.m.r. signal but the 13C isotope, which occurs in ordinary carbon to... 

C coupling has very little significance in everyday proton NMR interpretation, though it has been used in the past to crack specific problems by means of selective enrichment of a specific carbon during synthesis, with a greater than normal percentage of 13C isotope, which makes detection easy. 

Figure 9. The quadrupole mass spectrometer signal for volatile species released from 0.90 nm palladium acetate film as a function of 2 MeV He+ ion dose. Mass 15 is shown for both CH3 and CH4 because of overlap at m/e 16 with oxygen. Mass 31 is shown for C2H6 (13C isotope) because of overlap at m/e 30 with major fragments of other parent ions.

Corey et al. investigated the kinetic isotopic effect (KIE) in asymmetric dihydroxylation. 12C/13C KIE was measured for the dihydroxylation of styrene, p-nitrostyrene, and 4-methoxy-benzoate (Figure 7).197 The observed similar 12C/13C isotopic effect of two olefinic carbons... 

As can be seen in Table 1, all the program clusters also show very low 12C/13C isotopic ratios, which cannot be explained by first-dredge up alone, but they... 

Hansen, K.C., Schmitt-Ulms, G., Chalkley, R.J., Hirsch, J., Baldwin, M.A., and Burlingame, A.L. (2003) Mass spectrometric analysis of protein mixtures at low levels using cleavable 13C-isotope-coded affinity tag and multidimensional chromatography. Mol. Cell. Proteomics 2, 299-314. 

Broecker and Peng, p. 59 dlsscon = 7 dissolution constant in DJSS pcpcon = / carbonate precipitation constant disfac -. 01 scaling factor in dissolution rate eole/e 3/y delcorg 10 Fractionation by photosynthetic organises dcse = 2 Delta 13C Isotope ratio for sea eater, per eil... 

Non-isotopic and 13C Isotopic Approaches to Calculate Soil Organic Carbon Maintenance Requirement... 

Keywords Energy production 13C fractionation maintenance 13C isotopic discrimination... 

Most historical studies do not contain the detailed information needed to develop carbon budgets. They are also confounded by erosional losses, changes in the chemical methods to measure SOC, management-induced differences in bulk density, and different methods to calculate turnover kinetics. The consequences of these problems are that it is difficult to compare studies and calculate carbon turnover rates. To overcome these problems simplifying assumptions are often used (Clay et al. 2006 Johnson et al. 2006 Bolinder et al. 2007). Assumptions can reduce the usefulness of the findings. This chapter reviews non-isotopic and 13C isotopic approaches for determining SOC maintenance and implications of simplifying assumptions on SOC turnover calculations. 

The theoretic intensity of isotopic peaks due to the presence of several 13C isotopes may be easily calculated for any molecule. The intensity of the A + 2 peak (as a percentage of the A peak) for a compound with n carbon atoms may be established by the following formula ... 

When the number of carbon atoms is calculated on the basis of the M + 1 peak one should return to the M + 2 peak, to exclude contributions of 13C isotopes and estimate the number of oxygen atoms with greater precision. Let us consider as an example the mass spectmm represented in Fig. 5.21. 

The natural cycle of carbon involves compounds of the atmosphere, hydrosphere, lithosphere, and biosphere. A certain difference in the 13C isotope content exists between the samples, depending on their origin. To estimate the deviation from the average value of 13C isotope contents 8(%o) scale is used. The deviation may be calculated by Equation 5.14 ... 

The half-life of the process in Equation (8.32) is 5570 years. Following death, flora and fauna alike cease to breathe and eat, so the only 14C in a dead body will be the 14C it died with. And because the amounts of 14C decrease owing to radioactive decay, the amount of the 14C in a dead plant or person decreases whereas the amounts of the 12C and 13C isotopes do not. We see why the proportion of 14C decreases steadily as a function of time following the instant of death. 

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