Carbon isotopes preparation

Raw foods were freeze-dried and analyzed for carbon isotopes using mass spectrometry. Cooked foods were prepared following historic recipes, then were freeze-dried prior to analysis. For the trace element analysis, foods (both raw and cooked) were wet ashed using nitric acid in Teflon lined pressure vessels and digested in a CEM Microwave oven. Analysis of Sr, Zn, Fe, Ca and Mg was performed using Atomic Absorption Spectrometry in the Department of Geology, University of Calgary. 

White, J. W. (1992). Internal standard stable carbon isotope ratio method for determination of C-4 plant sugars in honey Collaborative trial study, and evaluation of improved protein preparation procedure. J. Assoc. Ojfic. Anal. Chem. 75,543-548. 

Reber, E. A. and Evershed, R. P. (2004a) How did Mississippians prepare maize The application of compound specific carbon isotopic analysis to absorbed pottery residues from several Mississippi Valley sites. Archaeometry 46, 19 33. 

Swanson, J. R., Carbon Isotope Analysis of Carbonaceous Compounds in Puget Sound and Lake Washington, PhD Thesis, University of Washington, 1980 and Swanson, J. R., Fairhall, A., Currie, L. A., Carbon Isotope Analysis of Sedimentary Polycyclic Aromatic Hydrocarbons (in preparation). 

An important criticism of the use of combustion trains is that combustion is not site specific, that is all atoms in the analyte end up in the gas transferred to the IRMS. For studies of carbon isotope effects this is invariably C02. The question is especially important for carbon isotope analysis because analyte molecules of interest usually contain several different kinds of carbon atoms and therefore combustion methods average or dilute the IE s of interest. Should site specific isotope ratios be required another method of sample preparation (usually much more tedious) is necessary. Combustion methods, however, are frequently used to study nitrogen and sulfur IE s because many organic molecules are singly substituted with these atoms. Obviously, oxygen isotope effects cannot be determined using combustion trains because external oxygen is employed. Rather some type of pyrolytic sample preparation is required. 

When compounds enriched in the heavy-carbon isotope 13C and the radioactive carbon isotopes nC and 14C became available about 60 years ago, they were soon put to use in tracing the pathway of carbon atoms through the citric acid cycle. One such experiment initiated the controversy over the role of citrate. Acetate labeled in the carboxyl group (designated [1-14C] acetate) was incubated aerobically with an animal tissue preparation. Acetate is enzymatically converted to acetyl-CoA in animal tissues, and the pathway of the... 

Recently, it was shown that ss-NMR spectroscopy can be used to determine the conformation of EpoB in the solid state [116]. The method relies on the measurement of intramolecular short H-H distances (in the range 1.8-3.0 A) from 2D CHHC correlations under MAS [117]. Regarding the sample preparation, a small amount of 13C labeled compound was diluted with EpoB with natural abundance of carbon isotopes. This reduces the signal to noise but, on the other hand, it excludes contributions from intermolecular H-H polarization transfer. Under these conditions, all CHHC cross-peaks result from intramolecular polarization transfer and reflect intramolecular interproton distances. 

Mass spectrometer precision was determined by making repeated measurements on a gas sample prepared by combustion of carbon isotope reference material NBS-22. The standard deviation of the mean derived from 10 consecutive measurements of this gas was 0.02 %o The error associated with the combustion and purification procedure was measured by replicate combustions of the NBS-22 reference material, which resulted in a standard deviation of 0 12 %o for five samples ITius, the overall precision associated with the mass spectrometric measurement of vs PDB was 0.12 %o, or in absolute terms, 1.3 ppm. Most of the error clearly was associated with the combustion and sample handling process. Since sealed-tube combustions have been shown to produce theoretical recoveries of carbon (33). these small errors most likely arise from handling the CO2 after it is released from the sample tube ... 

Silverman M. P. and Oyama V. 1. (1968) Automatic apparatus for sampling and preparing gases for mass spectral studies of carbon isotope fractionation during methane metabolism. Anal. Chem. 40, 1833-1877. 

M.H. Engel, R.J. Maynard (1989) Preparation of organic matter for stable carbon isotope analysis by sealed tube combustion A cautionary note. Anal. Chem. 61, 1996-1998... 

J 5). Average analytical variability of sample preparation and stable carbon isotope ratio analysis is +0.2 (1 ). A Carlo-Erba Model 1106 Elemental Analyzer was employed to determine percent organic carbon and nitrogen in each sediment sample. Analytical variation of sample analysis is 20 (17). 

In this context the present investigation focussed on the evaluation of a common analytical procedure adapted for the preparation of material utilizable for compound-specific stable carbon isotope analyses of riverine contaminants. Especially the sensitivity of the analytical method and the precision of the isotopic data obtained were studied. So far this analytical procedure has been applied to river water samples for qualitative and quantitative GC/MS analyses (Franke et al. 1995 Dsikowitzky et al. 2002). 

An important precondition for the successful determination of carbon isotope ratios is the prevention of isotopic shifts as a result of the analytical procedures applied. Therefore, five recovery experiments were performed in order to detect changes of the carbon isotope ratios during sample preparation and measurement. The compounds selected for these experiments are known riverine contaminants and comprise hexachlorobutadiene, several musk fragrances, phthalates and other plasticizers, a flame retardant and a pesticide. All recovery samples were spiked with concentrations between approx. 800 ng/L and 1500 ng/L for each compound representing a common abundance level in river systems. 

One simple test is to measure the level of radioactivity from the sample. Synthetic vanillin is not radioactive. However, natural vanilla, like all natural products, is. This is, of course, because atmospheric carbon dioxide contains some radioactive 14C formed by exposure to cosmic radiation in the upper atmosphere. Plants then incorporate this into their photosynthetic pathway and produce metabolites, which exhibit a low level of radioactivity. Synthetic vanillin is prepared from coal tar, which is not radioactive since the 14C has long since decayed. However, unscrupulous dealers know this and can synthesise radiolabelled or hot vanillin and dose it into synthetic material so that the level of radioactivity matches that of a natural sample. Another method of checking for naturalness must therefore be found. When plant enzymes synthesise molecules, they, like all catalysts, are susceptible to isotope effects. The vanilla plant is no exception and examination of the distribution of hydrogen and carbon isotopes in the vanillin molecule reveals that the heavier deuterium and 13C isotopes accumulate at certain specific sites. A suitable NMR spectrometer can determine the isotopic distribution in a sample and the cost of using 2H, 13C and 14C labelled synthetic materials to replicate the NMR spectra and radioactivity of natural vanillin in a synthetic sample would not be financially attractive. Furthermore, the 2H and 13C labelling patterns in the vanilla bean are different from those of other natural shikimate sources and so the NMR technique can also distinguish between vanillin from vanilla and vanillin produced by... 

The stable carbon isotope ratios of dissolved inorganic carbon (DIC) and benthic foraminiferal calcite generally are determined with isotope ratio gas mass spectrometers calibrated via NBS 19 international standard to the VPDB (Vienna Pee Dee Belemnite) scale. All values are given in 8-notation versus VPDB with an overall precision of measurements including sample preparation usually better than +0.06 and +0.1%o for calcite and DIC carbon isotopes, respectively. Except one single-specimen based dataset (Hill et al. 2004), all stable isotope data from papers referred to in this overview are from species-specific multi-specimens analyses. The number of specimens used for a single analysis depended on size and weight of species but usually varied between 2 and 25. 

The para-substituted carbon-14 labelled diazoacetophenones were prepared from the appropriate j 7ara-substituted benzoic acid-l- " C using conventional methods. A significant carbon isotope effect of 1.0120 0.0026 was found when the/ am-substituent... 

In the direct-determination procedure, carbonate carbon is first removed from the sediment subsample by treatment with dilute (3N) hydrochloric or phosphoric acid, washing and drying the carbonate-free residue, and then measuring the carbon content of the residue with an elemental analyzer. An alternative direct-determination procedure employs acid vapors to remove inorganic carbon (Yamamuro Kayanne, 1995). A related procedure employs direct reaction with HCl that is added to the sediment sample while it is in the tin boat that is used in the elemental analyzer. After reaction for 24 hours, the acid is evaporated prior to carbon analysis. Yet another alternative direct-determination method involves measuring the amount of CO2 released from carbonate-free sediment subsamples during off-line oxidation of the residual carbon in preparation for carbon isotope analysis. Off-line preparation lines for isotopic analyses can be manometrically calibrated to yield this measurement. Regardless of the procedure, TOC concentrations of lake sediments are usually expressed on a whole-sediment basis. 

Boutton, T. W., 1991. Stable isotope ratios of natural materials 1. Sample preparation and mass spectrometric analysis. In Coleman, D. C. B. Fry (eds.) Carbon Isotope Techniques. Academic Press, New York 155-171. 

Figure 9 gives a brief overview of the sample preparation procedure used in onr laboratory. One point of note is that drying is carried out at 40 °C, instead of the 80-KX) C that is normal in many laboratories. Experience from organic geochemistry indicates that the lower temperature is preferable to ensure that no volatile components are lost before analysis. Splits from the dry, powdered sample are also used for carbon isotopic analysis and RockEval pyrolysis (Talbot Livingstone, 1989 Talbot Laerdal, 2000 Fig. 9), in fact it is our practice to perform the analysis first, as %N data from the elemental analyser allows us to estimate how much sample needs to be weighed for the N-isotope determination. As little as 100 /xg N are required for analysis. 

Carbon dioxide for isotopic analysis prepared by combustion of organic material in sealed quartz tubes. Carbon-isotopic compositions reported in parts per thousand relative to the PDB standard. 

McGaw, B. A., Milne, E. and Duncan, G. J. (1988) A rapid method for the preparation of combustion samples for stable carbon isotope analysis by isotope ratio mass spectrometry. Biomedical and Environmental Mass Spectrometry, 16, 269-73. 

Like BSIA, two sample conversion systems are required depending on the element/s of interest. For example, Thermo Fisher Scientiflc (Waltham, MA) supplies a GC Combustion III (CIII) interface system for the preparation of samples for nitrogen and carbon isotope ratio measurements. They also have a High Temperature Conversion (TC) interface system for sample preparation for hydrogen and oxygen analysis [1,36,37]. 

Dautrarx et al. [24] discuss the successful analysis of carbon isotope values in heroin samples containing acetaminophen (a cutting agent used as an adulterant) using EA-IRMS and GC-IRMS. Potential isotopic fractionation effects during sample handling, preparation, and analysis were discussed. 

The first part of this chapter discusses CLA labeled with deuterium because only labeling with this hydrogen isotope has been described. In the second part, preparations of CLA labeled with carbon isotopes are discussed. The last section reports recent syntheses of CLA metabolites labeled with carbon 14. 

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