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Gas Chromatography/combustion/isotope Ratio Mass Spectrometry (gas + chromatography_ratio_mass_spectrometry)
Selected AbstractsDetermination of 13C/12C ratios of urinary excreted boldenone and its main metabolite 5,-androst-1-en-17,-ol-3-oneDRUG TESTING AND ANALYSIS, Issue 5 2010Thomas Piper Abstract Boldenone (androsta,1,4,dien,17,,ol,3,one, Bo) is an anabolic steroid known to have been used in cattle breeding or equine sport as a doping agent for many years. Although not clinically approved for human application, Bo or its main metabolite 5,-androst-1-en-17,-ol-3-one (BM1) were detected in several doping control samples. For more than 15 years the possibility of endogenous Bo production in human beings has been discussed. This is a challenging issue for doping control laboratories as Bo belongs to the list of prohibited substances of the World Anti-Doping Agency and therefore the chance for false positive testing is significant. By GC/C/IRMS (gas chromatography/combustion/isotope ratio mass spectrometry) it should be possible to analyze the 13C/12C ratio of either Bo or BM1 and to distinguish whether their source is endogenous or exogenous. Therefore a method was developed to determine the 13C/12C ratios of Bo, BM1, pregnanediol, androsterone, etiocholanolone, and testosterone from a single urine specimen. The validity of the method was ensured by repeated processing of urine fortified with 2,50 ng/mL Bo and BM1. The specificity of the method was ensured by gas chromatography/mass spectrometry determinations. Out of 23 samples investigated throughout the last four years, 11 showed 13C/12C ratios of Bo or BM1 inconsistent with an exogenous origin. Two of these samples were collected from the same athlete within a one-month interval, strongly indicating the chance of endogenous Bo production by this athlete. Copyright © 2010 John Wiley & Sons, Ltd. [source] 13C/12C Ratios of endogenous urinary steroids investigated for doping control purposesDRUG TESTING AND ANALYSIS, Issue 2 2009Thomas Piper Abstract In order to detect the misuse of endogenous anabolic steroids such as testosterone by athletes a total of n = 1734 suspicious urine samples were investigated by gas chromatography/combustion/isotope ratio mass spectrometry throughout the years 2005, 2006 and 2007. The 13C/12C ratio of a target substance (androsterone, a testosterone metabolite) was compared to the 13C/12C ratio of an endogenous reference compound (11,-hydroxyandrosterone). N = 1340 samples were investigated due to elevated testosterone/epitestosterone ratios, with n = 87 (6.5%) exceptional findings regarding their isotopic ratios. An additional n = 164 samples were investigated because of elevated dehydroepiandrosterone concentrations, with n = 2 (1.2%) exceptional findings. The remainder were subjected to isotope ratio analysis because of elevated androsterone levels or because this was requested by sports federations. Significant differences between female and male samples were found for the 13C/12C ratios of androsterone and 11,-hydroxyandrosterone but not for samples taken in or out of competition. A further n = 645 samples originating from other World Anti-Doping Agency accredited laboratories, mainly throughout Europe as well as South America, South Africa and Southeast Asia, were investigated. The 13C/12C ratios of the urinary steroids differ significantly for each geographical region, reflecting the dietary status of the individuals. The system stability over time has been tested by repeated injections of a standard solution and repeated processing of frozen stored blank urine. Despite a drift over time in absolute 13C/12C ratios, no significant change in the difference of 13C/12C (11,-hydroxyandrosterone) minus 13C/12C (androsterone) could be observed. Copyright © 2009 John Wiley & Sons, Ltd. Copyright © 2009 John Wiley & Sons, Ltd. [source] The turnover of carbohydrate carbon in a cultivated soil estimated by 13C natural abundancesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006D. Derrien Summary Understanding the chemical composition of soil organic matter (SOM) requires the determination of the dynamics of each class of compounds. We measured the dynamics of carbon in neutral carbohydrates by use of natural 13C labelling in an experimental wheat and maize sequence extending over 23 years. The isotopic composition of individual neutral monosaccharides was determined in hydrolysed particle-size fractions by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) of trimethylsilyl (TMS) derivatives. The sensitivity in terms of 13C/12C ratios ranged between 1 and 2, depending on the monosaccharide. The age distribution of neutral sugar carbon was very similar to that of total soil carbon. Particulate organic matter (POM) was characterized by the predominance of glucose and xylose of vegetal origin. In POM >,200 µm, the mean age of sugar-C (5 years) was slightly less than that of total carbon (7 years). Xylose was younger than glucose. The fine fraction 0,50 µm contained mainly glucose, arabinose, galactose, xylose, fucose and mannose, which had predominantly microbial origins. The mean age of carbohydrate carbon in the fraction 0,50 µm was between 60 and 100 years and was similar to that of total organic carbon (OC). No difference in the age of carbon between the individual monosaccharides was found. The POM fraction 50,200 µm had an intermediate signature and turnover. Considering the typical lability of carbohydrates, the relatively great age of carbohydrate carbon may be explained by physical or chemical protection from degradation, as well as by recycling of soil organic matter carbon by soil microbes. [source] Determination of the stable carbon isotopic compositions of 2-methyltetrols in ambient aerosols from the Changbai MountainsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2010Li Li Isoprene is one of the most important non-methane hydrocarbons (NMHCs) in the troposphere: it is a significant precursor of O3 and it affects the oxidative state of the atmosphere. The diastereoisomeric 2-methyltetrols, 2-methylthreitol and 2-methylerythritol, are marker compounds of the photooxidation products of atmospheric isoprene. In order to obtain valuable information on the ,13C value of isoprene in the atmosphere, the stable carbon isotopic compositions of the 2-methyltetrols in ambient aerosols were investigated. The 2-methyltetrols were extracted from filter samples and derivatized with methylboronic acid, and the ,13C values of the methylboronate derivatives were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The ,13C values of the 2-methyltetrols were then calculated through a simple mass balance equation between the 2-methyltetrols, methylboronic acid and the methylboronates. The ,13C values of the 2-methyltetrols in aerosol samples collected at the Changbai Mountain Nature Reserves in eastern China were found to be ,24.66,±,0.90, and ,24.53,±,1.08, for 2-methylerythritol and 2-methylthreitol, respectively. Based on the measured isotopic composition of the 2-methyltetrols, the average ,13C value of atmospheric isoprene is inferred to be close to or slightly heavier than ,24.66, at the collection site during the sampling period. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simultaneous measurement of 13C- and 15N-isotopic enrichments of threonine by mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2009Jean-Philippe Godin Under conditions of high isotopic dilution, e.g. in a tracer study, the ability to determine accurately and quantitatively small variations in isotopic enrichments of differently labelled chemical compounds (e.g. 13C and 15N in threonine) in a single run by gas chromatography/mass spectrometry (GC/MS) is desirable but remains a technological challenge. Here, we report a new, rapid and simple GC/MS method for simultaneously measuring the isotopic enrichments of doubly labelled threonine ([U13C] and 15N) with isotopic enrichment lower than 1.5 Molar Percent Excess (MPE). The long-term reproducibility measured was around 0.09 MPE for both tracers (throughout a 6 week period). The intra-day repeatability was lower than 0.05 and 0.06 MPE for [U13C]-Thr and 15N-Thr, respectively. To calculate both isotopic enrichments, two modes of calculations were used: one based on work by Rosenblatt et al. in 1992 and the other one using a matrix approach. Both methods gave similar results (ANOVA, P >0.05) with close precision for each mode of calculation. The GC/MS method was then used to investigate the differential utilization of threonine in different organs according to its route of administration in minipigs after administration of both tracers. In plasma samples, the lowest isotopic enrichment measured between two successive time points was at 0.01 and 0.02 MPE for [U13C]-Thr and 15N-Thr, respectively. Moreover, the accuracy of GC/MS 13C-isotopic enrichment measured was validated by analyzing the same plasma samples by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Statistical analysis showed that both techniques gave the same results (ANOVA, P >0.05). This new GC/MS method offers the possibility to measure 13C- and 15N-isotopic enrichments with higher throughput, and using a lower amount of sample, than using GC/C/IRMS. Copyright © 2009 John Wiley & Sons, Ltd. [source] Inter-laboratory comparison of elemental analysis and gas chromatography/combustion/isotope ratio mass spectrometry.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 200915N measurements of selected compounds for the development of an isotopic Grob test An inter-laboratory exercise was carried out by a consortium of five European laboratories to establish a set of compounds, suitable for calibrating gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) devices, to be used as isotopic reference materials for hydrogen, carbon, nitrogen and oxygen stable isotope measurements. The set of compounds was chosen with the aim of developing a mixture of reference materials to be used in analytical protocols to check for food and beverage authentication. The exercise was organized in several steps to achieve the certification level: the first step consisted of the a priori selection of chemical compounds on the basis of the scientific literature and successive GC tests to set the analytical conditions for each single compound and the mixture. After elimination of the compounds that turned out to be unsuitable in a multi-compound mixture, some additional oxygen- and nitrogen-containing substances were added to complete the range of calibration isotopes. The results of ,13C determinations for the entire set of reference compounds have previously been published, while the ,D and ,18O determinations were unsuccessful and after statistical analysis of the data the results did not reach the level required for certification. In the present paper we present the results of an inter-laboratory exercise to identify and test the set of nitrogen-containing compounds present in the mixture developed for use as reference materials for the validation of GC-C-IRMS analyses in individual laboratories. Copyright © 2009 John Wiley & Sons, Ltd. [source] Determination of 13C/12C ratios of endogenous urinary steroids: method validation, reference population and application to doping control purposesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2008Thomas Piper The application of a comprehensive gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS)-based method for stable carbon isotopes of endogenous urinary steroids is presented. The key element in sample preparation is the consecutive cleanup with high-performance liquid chromatography (HPLC) of underivatized and acetylated steroids, which allows the isolation of ten analytes (11, -hydroxyandrosterone, 5, -androst-16-en-3, -ol, pregnanediol, androsterone, etiocholanolone, testosterone, epitestosterone, 5, -androstane-3,,17, -diol, 5, -androstane-3,,17, -diol and dehydroepiandrosterone) from a single urine specimen. These steroids are of particular importance to doping controls as they enable the sensitive and retrospective detection of steroid abuse by athletes. Depending on the biological background, the determination limit for all steroids ranges from 5 to 10,ng/mL for a 10,mL specimen. The method is validated by means of linear mixing models for each steroid, which covers repeatability and reproducibility. Specificity was further demonstrated by gas chromatography/mass spectrometry (GC/MS) for each analyte, and no influence of the sample preparation or the quantity of analyte on carbon isotope ratios was observed. In order to determine naturally occurring 13C/12C ratios of all implemented steroids, a reference population of n,=,61 subjects was measured to enable the calculation of reference limits for all relevant steroidal , values. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of the 13C natural abundance of CO2 gas from sparkling drinks by gas chromatography/combustion/isotope ratio mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2005Giovanni Calderone A simple and rapid method to measure naturally occurring ,13C values of headspace CO2 of sparkling drinks has been set up, using direct injections on a gas chromatograph coupled to an isotope ratio mass spectrometer, through a combustion interface (GC/C/IRMS). We tested the method on CO2 gas from several origins. No significant isotopic fractionation was observed nor influences by secondary compounds eventually present in the gas phase. Standard deviation for these measurements was found to be <0.1,. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||