Nitrogen isotope analysis sample preparation

Fig. 1.9 Tamsin O Connell and students preparing samples of bone and hair for carbon and nitrogen isotopes analysis in the Dorothy Garrod Laboratory for Isotopic Analysis at Cambridge University...

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. 

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). 

As mentioned in the Section 1, physico-chemical methodology for quantitative analysis of plant hormone focuses primarily on GC-SIM, although HPLC with selective fluorescence detection continues to be used for lAA analysis in some laboratories. Procedures, such as the 2-methylindolo-a-pyrone assay for lAA analysis [82], are now rarely utilised. With the exception of ethylene quantification [2] there is little use of non-MS-based GC detection techniques, despite the fact that selective analysis at the picogram level is achieved for ABA with an electron capture detector [83], and lAA and cytokinins with a nitrogen phosphorus detector [84,85]. The reason for the demise of these GC procedures is that the detectors are destructive and this precludes the reliable recovery of labelled internal standards for radioassay and isotopic dilution analysis. The usual compromise was to take two aliquots of the purified samples, one for GC analysis and the other for the determination of radioactivity. The accuracy of this approach is dependent upon the questionable assumption that the radioactivity in the purified sample is associated exclusively with the compound under study. In an attempt to circumvent this problem, a double standard isotope dilution procedure was devised for the quantitative analysis of lAA in which one internal standard was used to correct for losses during sample preparation and a second for GC quantification [86]. This procedure was used in several... 

Determining the N-isotopic composition of sedimentary OM requires that N2 gas be prepared from the sample. The gas is then fed into a mass spectrometer for analysis. An excellent, comprehensive review of mass spectrometry, and the various sample preparation techniques that may be used for N-isotope analysis, is given in Owens (1987). Attention here will be confined to some of the more pertinent practical aspects of isotopic analysis with particular reference to the system used at UB. As indicated in the Introduction, the adoption of nitrogen isotopes as a standard technique in the earth and biological sciences was hindered by the time-consuming, off-line preparation techniques that most studies required. A few labs have stuck to the original, wet-chemistry sample preparation, feeling... 

Nevins, J. L., M. A. Altabet J. J. McCarthy, 1985. Nitrogen isotope ratio analysis of small samples sample preparation and calibration. Analyt. Chem. 57 2143-2145. 

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... 

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. 

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