Isotopic correction factor

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). 

Craig, H. (1957a). Isotopic standards for carbon and correction factors for mass-spectrometric analysis of carbon dioxide. Geochim. Cosmochim. Acta 12, 133-149. 

Accuracy for all thorium measurements by TIMS is limited by the absence of an appropriate normalization isotope ratio for internal correction of instrumental mass fractionation. However, external mass fractionation correction factors may be obtained via analysis of suitable thorium standards, such as the UC-Santa Cruz and IRMM standards (Raptis et al. 1998) for °Th/ Th, and these corrections are usually small but significant (< few %o/amu). For very high precision analysis, the inability to perform an internal mass fractionation correction is probably the major limitation of all of the methods for thorium isotope analysis discussed above. For this reason, MC-ICPMS techniques where various methods for external mass fractionation correction are available, provide improved accuracy and precision for Th isotope determinations (Luo et al. 1997 Pietruszka et al. 2002). 

Calculate the observed isotope ratio, R , for the sample, and multiply by the mass bias correction factor to obtain the true isotope ratio, R Hence, calculate C for the sample using Eqn. B.4. 

Isotope ratio analysis, 131-134 abundance, 131 correction factor, 131 detector dead time, 132-133 mass bias, 131. 132(f) precision of, 133... 

Interference Corrections. In certain cases, the y-rays of one element isotope are close to the y-ray energy of an isotope used to determine another element. In these cases, it was necessary to correct for this interference. Subroutines for interference corrections were added to SPECTRA to eliminate performing such corrections manually. The correction factors used were normally derived from nuclear data information. But we did check these corrections by irradiating mixtures of these elements in various concentrations. The interference corrections used are shown in Table VI. The correction for 28Al on 27Mg was determined empirically because it was specific to the irradiation location in the PBR. 

It may also be surprising how easily this racemization may occur. Friedman and Liardon (126) studied the racemization kinetics for various amino acid residues in alkali-treated soybean proteins. They report that the racemization of serine, when exposed to 0.1M NaOH at 75°C, is nearly complete after just 60 minutes. However, caution must be used when examining apparent racemization rates for protein-bound amino acids. Liardon et al. (127) have also reported that the classic acid hydrolysis, employed to liberate constituent amino acids, causes amino acids to racemize to various degrees. This will necessarily result in D-isomer determinations that are biased high. Widely applicable correction factors are not possible since the racemization behavior of free amino acids is different from that of amino acid residues in proteins (which can be further affected by sequence). Of course, this is not a problem for free amino acid isomer determinations since the acid hydrolysis is unnecessary. Liardon et al. also describe an isotopic labeling/mass spectrometric method for determining true racemization rates unbiased by the acid hydrolysis. For an extensive and excellent review of the nutritional implications of the racemization of amino acids in foods, the reader is directed to a review article written by Man and Bada (128). 

Figure 3 is an illustration of some calculated [H0M76] thermal correction factors for ground-state neutron-capture cross sections for a number of isotopes near the line of stability. From this figure it is clear that these correction factors can be significant. For the benefit of anyone who might like to attack this problem. Table I summarizes some of what we consider to be the most important quantities to better refine as input to the s-process. 

Figure 3 Correction factors, f, for the neutron-capture cross section for various Isotopes due to the thermal population of excited states at stellar temperatures (from [H0W76]). Isotopes with f > 10% are labeled.

SIMS is mostly employed for microlocal analytical investigations. For example, isotope ratio measurements by SIMS have been performed in nuclear forensic studies to determine the age of Pu particles." For the age determination of Pu particles, relative sensitivity coefficients (RSC) were determined as correction factors for the different ionization efficiency of Pu compared to U. The age of a sample of known origin calculated from Pu/ " and °Pu/ U ratios agreed well with the reported age of 2.3 years." SIMS was employed for oxygen isotope ratio measurements in three different uranium oxide microparticles of nuclear forensic interest by Betti s working group." The... 

This relationship is called the specific activity model. Its main advantage is its independence of the kind of animal or plant. The model can also be applied if the radionuclides show a similar behaviour to stable isotopes of other elements, for example 90sr2+ and Ca +. Different behaviour can be taken into account by a correction factor (called the observed ratio OR) ... 

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