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Gas Chromatography-combustion-isotope Ratio Mass Spectrometry (gas + chromatography-combustion-isotope_ratio_mass_spectrometry)
Selected AbstractsLiquid and gas chromatography coupled to isotope ratio mass spectrometry for the determination of 13C,valine isotopic ratios in complex biological samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2008Jean-Philippe Godin Abstract On-line gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) is commonly used to measure isotopic ratios at natural abundance as well as for tracer studies in nutritional and medical research. However, high-precision 13C isotopic enrichment can also be measured by liquid chromatography-isotope ratio mass spectrometry (LC-IRMS). Indeed, LC-IRMS can be used, as shown by the new method reported here, to obtain a baseline separation and to measure 13C isotopic enrichment of underivatised amino acids (Asp, Thr,Ser, Glu, Pro, Gly, Ala, Cys and Val). In case of Val, at natural abundance, the SD(,13C) reported with this method was found to be below 1, . Another key feature of the new LC-IRMS method reported in this paper is the comparison of the LC-IRMS approach with the conventional GC-C-IRMS determination. To perform this comparative study, isotopic enrichments were measured from underivatised Val and its N(O, S)-ethoxycarbonyl ethyl ester derivative. Between 0.0 and 1.0 molar percent excess (MPE) (,13C = , 12.3 to 150.8,), the calculated root-mean-square (rms) of SD was 0.38 and 0.46, and the calculated rms of accuracy was 0.023 and 0.005 MPE, respectively, for GC-C-IRMS and LC-IRMS. Both systems measured accurately low isotopic enrichments (0.002 atom percent excess (APE)) with an SD (APE) of 0.0004. To correlate the relative (,13C) and absolute (atom%, APE and MPE) isotopic enrichment of Val measured by the GC-C-IRMS and LC-IRMS devices, mathematical equations showing the slope and intercept of the curves were established and validated with experimental data between 0.0 to 2.3 MPE. Finally, both GC-C-IRMS and LC-IRMS instruments were also used to assess isotopic enrichment of protein-bound 13C,Val in tibial epiphysis in a tracer study performed in rats. Isotopic enrichments measured by LC-IRMS and GC-C-IRMS were not statistically different (p > 0.05). The results of this work indicate that the LC-IRMS was successful for high-precision 13C isotopic measurements in tracer studies giving 13C isotopic enrichment similar to the GC-C-IRMS but without the step of GC derivatisation. Therefore, for clinical studies requiring high-precision isotopic measurement, the LC-IRMS is the method of choice to measure the isotopic ratio. Copyright © 2008 John Wiley & Sons, Ltd. [source] Critical assessment of the applicability of gas chromatography-combustion-isotope ratio mass spectrometry to determine amino sugar dynamics in soilRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2009Charlotte Decock Amino sugars in soils have been used as markers of microbial necromass and to determine the relative contribution of bacterial and fungal residues to soil organic matter. However, little is known about the dynamics of amino sugars in soil. This is partly because of a lack of adequate techniques to determine ,turnover rates' of amino sugars in soil. We conducted an incubation experiment where 13C-labeled organic substrates of different quality were added to a sandy soil. The objectives were to evaluate the applicability of compound-specific stable isotope analysis via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) for the determination of 13C amino sugars and to demonstrate amino sugar dynamics in soil. We found total analytical errors between 0.8 and 2.6, for the ,13C-values of the soil amino sugars as a result of the required ,13C-corrections for isotopic alterations due to derivatization, isotopic fractionation and analytical conditions. Furthermore, the ,13C-values of internal standards in samples determined via GC-C-IRMS deviated considerably from the ,13C-values of the pure compounds determined via elemental analyzer IRMS (with a variation of 9 to 10, between the first and third quartile among all samples). This questions the applicability of GC-C-IRMS for soil amino sugar analysis. Liquid chromatography-combustion-IRMS (LC-C-IRMS) might be a promising alternative since derivatization, one of the main sources of error when using GC-C-IRMS, is eliminated from the procedure. The high 13C-enrichment of the substrate allowed for the detection of very high 13C-labels in soil amino sugars after 1 week of incubation, while no significant differences in amino sugar concentrations over time and across treatments were observed. This suggests steady-state conditions upon substrate addition, i.e. amino sugar formation equalled amino sugar decomposition. Furthermore, higher quality substrates seemed to favor the production of fungal-derived amino sugars. Copyright © 2009 John Wiley & Sons, Ltd. [source] Off-line pyrolysis and compound-specific stable carbon isotope analysis of lignin moieties: a new method for determining the fate of lignin residues in soil,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2008Jennifer A. J. Dungait Off-line pyrolysis was used to liberate lignin moieties from dung and soil and, after trimethylsilylation, the ,13C values of these derivatives were determined by gas chromatography-combustion-isotope ratio mass spectrometry. Initial ,13C values determined for 4-vinylphenol, syringol, 4-vinylguaiacol, 4-acetylsyringol, 4-vinylsyringol, 4-(2- Z -propenyl)syringol, 4-(2- E -propenyl)syringol and 4-(2-propenone)syringol pyrolysis products of the lignin polyphenol structure from C4 (,13Cbulk,=,,12.6%) and C3 (,13Cbulk,=,,30.1,) dung confirmed the robust and reproducible nature of the off-line preparation technique. C4 dung was used as a treatment in a randomised field experiment to assess the short-term sequestration of dung carbon in managed grasslands. Since lignin was on average 3.5, depleted in 13C compared with bulk dung ,13C values, this may have resulted in an under-estimation of dung C incorporation based on bulk ,13C values. Therefore, an investigation of the compound-specific ,13C values of dung-derived lignin moieties extracted from soils sampled up to 372 days was undertaken. ,13C values between lignin moieties extracted from treated and untreated soils showed that dung-derived lignin was not especially resistant to degradation and suggested that individual moieties of the lignin macromolecule must: (i) move into soil, (ii) be degraded, or (iii) be transformed diagenetically at different rates. This adds to a gathering body of evidence that lignin is not particularly stable in soils, which has considerable significance for the perceived role of different biochemical components in the cycling of C in soils. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||