Isotopic analyses calculation

The usual procedure for radiocarbon dating is to bum a tiny sample of the object to be dated, collect the CO2 that is produced, and compare its rate of radioactive decay with that of a fresh CO2 sample. The ratio of counts gives Nq jN, which can then be substituted into Equation to calculate t. Mass spectroscopic isotope analysis can also be used to obtain the Nq jN value, as Example illustrates. 

Corrections for instrumentally-produced mass fractionation that preserve natural mass dependent fractionation can be approached in one of two ways a double-spike method, which allows for rigorous calculation of instrumental mass fractionation (e.g., Dodson 1963 Compston and Oversby 1969 Eugster et al. 1969 Gale 1970 Hamelin et al. 1985 Galer 1999 see section Double-spike analysis ), or an empirical adjustment, based on comparison with isotopic analysis of standards (Dixon et al. 1993 Taylor et al. 1992 1993). The empirical approach assumes that standards and samples fractionate to the same degree during isotopic analysis, requiring carefully controlled analysis conditions. Such approaches are commonly used for Pb isotope work. However, it is important to stress that the precision and accuracy of isotope ratios determined on unknown samples may be very difficult to evaluate because each filament load in a TIMS analysis is different. 

In an attempt to establish the fluid and metal sources and to help constrain a genetic model, stable isotope studies (O, Pb, S) were conducted on selected occurrences. Oxygen isotope analysis of quartz vein material from eight separate occurrences yielded values of 10.9-16.0%o. Assuming equilibrium between quartz and the hydrothermal fluid, the values calculated for the mineralizing fluids, at temperatures between 300-400°C, range between 4.0 and 11.9%o. This overlaps accepted values for both magmatic and metamorphic fluids. 

Furthermore, isotope analysis is relevant for determining the atomic weight (Ar(E)) of elements. The Ar(E) is the average of all masses of all naturally occurring stable isotopes (taking into account the abundances of isotopes) of a chemical element (see Appendix I10). By consideration of the masses of isotopes (/ ,) and the known relative abundances of all stable isotopes (Xi) with i = 1 to n of a selected chemical element, the average atomic weight (Ar(E)) of this element can be calculated ... 

Isotope dilution analysis is applied to the following analysis. Calculate the amount of the compound Y present in the sample and express your answer as percent by weight. A 1-g sample is analyzed for compound Y, molecular weight of 150. A derivative is formed of compound Y and the added radioactive Y (1.5 mCi at a specific activity of 3 mCi/mmol). The derivative, molecular weight of 150 (1 mol of compound Y per mole of derivative), is recrystallized until pure. It has a specific activity of 4.44 x 103 dpm/mg. 

The experimental KIEs were determined for the aliphatic Claisen rearrangement in p-cymene at 120°C and for the aromatic Claisen rearrangement either neat at 170°C or in diphenyl ether at 220°C. Changes in 2H, 13C or 170 composition were determined for unreacted substrates. For carbon analysis of allyl vinyl ether the C5 carbon was used as an internal standard. The C4 atom and rneta aryl protons were used as references in analysis of allyl phenyl ether. The 170 analysis was based on a new methodology. The results are summarized in Table 1, along with predicted isotope effects calculated for experimental temperatures by means of different computational methods. The absolute values of predicted isotope effects for C4 and C5 atoms varied with theoretical level and all isotope effects were rescaled to get reference effects equal to 1.000. 

Isotope ratio measurements were employed for the quantification of analytical data using the isotope dilution strategy. For example, isotope dilution analysis was developed by Sanz-Medel s group for the determination of selenomethionine in Se enriched yeast material by HPLC-ICP-MS using a Se-enriched selenomethionine spike obtained by growing yeast on a Se rich culture medium. For Cr(III)/Cr(VI) determination in yeast, Caruso et al employed the double spike species specific isotope dilution technique measured by HPLC-ICP-MS. The isotope pattern deconvolution approach applied in this work delivers a more intuitive and elegant solution to an otherwise complex data analysis without the need for iterative calculations as widely practised in double spike isotope dilution. The results are in exact agreement with the conventional isotope dilution calculations. ... 

The use of stable isotopic tracers is based on following a labeled compound from one pool (the source pool) to another (the target pool) (Sheppard, 1962). The principles described below are the same regardless of whether one is measuring rates in the water column or sediment. What changes are the protocols used to isolate the different fractions prior to isotopic analysis. The basic equation to calculate the flux rate from one pool to another is ... 

Analysis of Isotope-effect Calculations Illustrated with Exchange Equilibria Among Oxynitrogen Compounds... 

Here is how SAL works Samples are received in a reception and storage room, then routed to the appropriate wet chemical analysis laboratory. There, they are analysed for uranium, thorium or plutonium content, and purified aliquots (portions of the sample) are prepared for the isotopic analysis of three elements. Isotopic analyses are performed routinely by mass spectrometry, and radiometric techniques are used for back-up. Emission spectrography serves to detect the presence of impurities which could interfere with the measurements and thus distort the results of the chemical and isotopic analysis of uranium, thorium and plutonium. Complex calculations and quality checks are performed on minicomputers, which are connected in a network to a central laboratory mini-computer. A central laboratory data system stores and provides analytical reports and enables the quality of the analyses and the status of the flow of samples through the laboratory at any time to be monitored. 

Detector saturation can effect both quantitative and qualitative data analysis, and each of these effects should be appreciated. The effect on sample quanti-tation is intuitive, where for instance a twofold increase in sample concentration produces a less than twofold increase in response. This will cause a flattening of calibration curves at higher concentrations. For API techniques, source saturation (or ion suppression) is another source of response saturation independent of detector saturation. Detector saturation can also effect qualitative measurements such as mass accuracy and isotope ratio calculations. In the former, when a mass spectral peak that has some finite resolution stalls to saturate the detector the peak-top calculations that provide the m/ measurement of the peak will become ambiguous. Likewise, it is possible that as one isotope of an ion starts to saturate the detector, adjacent isotopes in the distribution will still provide a linear response. The result of this is that incorrect isotope ratios will be obtained. Changes in relative isotope ratios of individual spectra across a chromatographic peak is an indicator of possible detector saturation. 

For secondary isotope effects, no simple one-frequency vibrational models have been devised analogous to the Swain et al. [34] treatment for primary isotope ef fects. Still, some vibrational analysis calculations tend to give Thd close to 1.44. 

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