Carbon-nitrogen ratios sample 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. 

Nitrogen to carbon ratios in humic acids are generally slightly higher than N/C ratios in fulvic acids. In stable residues, most of the nitrogen occurs in the hydrolyzable fraction and is lost during sample preparation. Therefore, the N/C ratios of stable residues are always considerably less than the N/C ratios of humic acids. 

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). 

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]. 

The combination of gas chromatography and an isotope ratio measurement mass spectrometer (ir/n-GC-MS) was used to study the detoxification and degradation pathways of tropane alkaloids involving iV-demethylation to the respective nor-compounds. Molinie et al. developed protocols for sample preparation, including liquid-hquid and SPE extraction, and analysis of the kinetic isotope effects (KlEs) with irm-GC-MS and ir/M-elemental analysis (EA)-MS [100]. Degradation experiments were performed with a Pseudomonas strain that uses tropane alkaloids as sole source of carbon and nitrogen. The authors found that liquid-liquid extraction from the aqueous medium in combination with ir/n-GC-MS was the most convenient method for measurement of the ratio. Later, Kosieradzka... 

The samples were prepared by adding 100 grams of plastic sample to 600 grams of mature soil compost in a 5-liter glass jar. The mature compost, 2-3 months old, had a pH of 8.7, ash content of 35%, and Carbon/Nitrogen (C/N) ratio of 10. The C/N ratio was calculated based upon carbon dioxide and ammonia measurements taken with the Sol vita instrument on the compost at the beginning of the test. Solvita is an easy-to-use test that measures both carbon dioxide (CO2) and ammonia (NH3) levels in the soil and also indicates a Maturity Index value. The index is useful for maturity level of the compost soil (Solvita Test Kit 2013). The blank compost had a Solvita overall maturity index of 7... 

Samples of various stoichiometries were prepared by sintering mixtures of the hydrides and graphite in the appropriate ratios under vacuum ca. 10 bar) at 1673 K. Determination of carbon (combustion), oxygen and nitrogen (reducing fusion under He), as well as phase analysis (X-ray diffraction and metallography) are mentioned, but no details were given. Elementary analysis indicated metallic impurities in amoimts smaller than 300 parts per million. 

Although spectroscopic methods are far less precise than IRMS for isotope ratio measurements, they can have advantages in terms of costs and ease of operation. These techniques also remove the laborious chemical preparation required for conventional IRMS. They are most commonly applied to the analysis of samples that are artificially enriched in the heavier isotopes of nitrogen, carbon, and oxygen. 

The NMR sensitivity depends on the magnetogyric ratio and the natural abundance of the NMR active nuclei. Table 3.1 lists the properties of some of the nuclei that are of particular interest to polymer chemists. The sensitivity is highest for protons and fluorines, but nuclei such as carbon, silicon and phosphorus can be routinely studied. Deuterium and nitrogen have poor sensitivities, but they provide valuable insight into the structure and dynamics of polymers when isotopically enriched samples are prepared. 

Samples were prepared by the sol-gel method by hydrolysis of iron and lanthanum nitrate with a potassium carbonate solution (6 mol.L" ) to get solids with lanthanum to iron molar ratio of 0.1. The solids were then calcined under nitrogen flow at 600°C, for 2 h. The sample named CK was obtained by the addition of the reactants solutions on a beaker with water, imder stirring. Other two samples were prepared by changing the order of mixing the reactants the first one (CKM sample) was obtained by adding the... 

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