Amount-dependent isotopic fractionation during compound-specific isotope analysis (original) (raw)
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Biological Mass Spectrometry, 1985
Stable isotope tracer methods are gaining popularity in many fields, including environmental science, agriculture and medicine. This is particularly true in the clinical sciences, where the use of radioisotopes can be precluded on ethical grounds and I3C and "N tracers are being used more frequently for metabolic studies. Mass spectrometry is the preferred technique for isotope analysis. Sample preparation techniques for classical isotope ratio mass spectrometry are often tedious and can involve the use of complex vacuum apparatus that is quite foreign to the biological chemist. Organic gas chromatography/mass spectrometry (GUMS) overcomes many sample preparation problems but may lack the performance needed for isotope analysis. This paper describes the analysis of I3C using an automatic elemental gas chromatograph interfaced to an isotope ratio mass spectrometer, a system which was developed initially for the analysis of "N. Details of the residual gas background, peak broadening due to high carrier gas pressures, mass spectral linearity and response to changing sample peak heights and variations of the measured isotope ratio with sample pressure are described. Sensitivity and performance data (reproducibility f 0.62% at natural abundance) are also given. The potential of this system for other gas chromatographic applications, automatic data handling and the possible simultaneous analysis of "C and "N are also discussed.
Applied gas chromatography coupled to isotope ratio mass spectrometry
Compound-specific isotope analysis (CSIA) by isotope ratio mass spectrometry (IRMS) following on-line combustion (C) of compounds separated by gas chromatography (GC) is a relatively young analytical method. Due to its ability to measure isotope distribution at natural abundance level with great accuracy and high precision, GC/C–IRMS has increasingly become the method of choice in authenticity control of foodstuffs and determination of origin in archaeology, geochemistry, and environmental chemistry. In combination with stable isotope labelled compounds, GC/C–IRMS is also used more and more in biochemical and biomedical application as it offers a reliable and risk-free alternative to the use of radioactive tracers. The literature on these topics is reviewed from the advent of commercial GC/C–IRMS systems in 1990 up to the beginning of 1998. Demands on sample preparation and quality of GC separation for GC/C–IRMS are discussed also.
Mass Spectrometry Reviews, 2007
Among the different disciplines covered by mass spectrometry, measurement of 13C/12C isotopic ratio crosses a large section of disciplines from a tool revealing the origin of compounds to more recent approaches such as metabolomics and proteomics. Isotope ratio mass spectrometry (IRMS) and molecular mass spectrometry (MS) are the two most mature techniques for 13C isotopic analysis of compounds, respectively, for high and low-isotopic precision. For the sample introduction, the coupling of gas chromatography (GC) to either IRMS or MS is state of the art technique for targeted isotopic analysis of volatile analytes. However, liquid chromatography (LC) also needs to be considered as a tool for the sample introduction into IRMS or MS for 13C isotopic analyses of non-volatile analytes at natural abundance as well as for 13C-labeled compounds. This review presents the past and the current processes used to perform 13C isotopic analysis in combination with LC. It gives particular attention to the combination of LC with IRMS which started in the 1990's with the moving wire transport, then subsequently moved to the chemical reaction interface (CRI) and was made commercially available in 2004 with the wet chemical oxidation interface (LC-IRMS). The LC-IRMS method development is also discussed in this review, including the possible approaches for increasing selectivity and efficiency, for example, using a 100% aqueous mobile phase for the LC separation. In addition, applications for measuring 13C isotopic enrichments using atmospheric pressure LC-MS instruments with a quadrupole, a time-of-flight, and an ion trap analyzer are also discussed as well as a LC-ICPMS using a prototype instrument with two quadrupoles. © 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:751–774, 2007
… in Mass Spectrometry, 2009
Compound-specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds; for instance, polycyclic aromatic hydrocarbons (PAHs) in aerosols. This could be a valuable tool in source apportionment of particulate matter (PM) air pollution. Because gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) analysis requires an amount of at least 10 ng of an individual PAH, a high concentration of PAHs in the injected extract is needed. When the concentration is low a large volume injector creates the possibility of introducing a satisfactory amount of individual PAHs. In this study a temperature-programmable injector was coupled to GC-C-IRMS and injection parameters (solvent level, transfer column flow, transfers time) were optimised using six solid aromatic compounds (anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene) dissolved in n-pentane and EPA 610 reference mixture. CSIA results for solid PAHs were compared with results obtained for the single components analysed by elemental analysis-isotope ratio mass spectrometry. The injection method was validated for two sample injection volumes, 50 and 100 mL. This method was also compared with commonly used splitless injection. To be included in the study, measurements had to have an uncertainty lower than 0.5% for d VPDB 13 C and a minimum peak height of 200 mV. The lower concentration limits at which these criteria were fulfilled for PAHs were 30 mg/L for 1 mL in splitless injection and 0.3 and 0.2 mg/L for 50 and 100 mL, respectively, in large volume injection.
On-line recording of13C/12C ratios and mass spectra in one gas chromatographic analysis
Journal of High Resolution Chromatography, 1995
An isotope ratio mass spectrometer and an ion trap mass spectrometer have been coupled in parallel to one gas chromatograph. Using this arrangement both the 13C/12C ratio and the mass spectrum of a given compound can be measured simultaneously under identical gas chromatographic conditions. Although column connection fittings are employed to split the capillary eluate, chromatographic performance was barely impaired. Development of the system has been monitored by recording 6I3C values of the constituents of Grob test mixture no. 2. The accuracy and reliability of system performance has also been tested.
Determination of 13 C/ 12 C Carbon Isotope Ratio
Analytical Chemistry, 2006
Isotopomers 12 CO 2 and 13 CO 2 absorbed into polystyrene films provide narrow, sharp, and well-resolved IR absorption bands for the ν 3 antisymmetric stretching mode. This is exploited to set up an inexpensive FT-IR-based method for the measurement of the carbon isotope ratio. Accuracy of 2.5‰ δ 13 C units is readily achieved already at a low resolution of 2 cm -1 .
Analytical Chemistry, 2003
Compound-specific carbon isotope analysis (CSIA) has become an important tool in biological, archeological, and geological studies as well as in forensics, food sciences, and organic chemistry. If sensitivity could be enhanced, CSIA would further have an improved potential for environmental applications such as, for example, in situ remediation studies to assess contaminated environments, identification of pollutant degradation pathways and kinetics, distinction between degradation/formation mechanisms, or, verification of contaminant sources. With this goal in mind, we have developed methods to determine D 13 C values of commonly reported groundwater contaminants in low-microgram per liter concentrations. Several injection and preconcentration techniques were evaluated for this purpose, i.e., on-column injection, split/ splitless injection, solid-phase microextraction (SPME), and purge and trap (P&T) in combination with gas chromatography-isotope ratio mass spectrometry. The D 13 C values of the target compounds were determined by liquid injections of the analytes dissolved in diethyl ether or, in the case of P&T and SPME, by extraction from water spiked with the analytes. P&T extraction was the most efficient preconcentration technique reaching method detection limits (MDLs) from 0.25 to 5.0 µg/L. These are the lowest MDLs reported so far for continuous-flow isotope ratio determinations, using a commercially available and fully automated system. Isotopic fractionation resulting from preconcentration and injection was investigated and quantified for the priority groundwater pollutants methyl tert-butyl ether (MTBE), chloroform, tetrachloromethane, chlorinated ethylenes, benzene, and toluene. The isotopic fractionations caused by the extraction techniques were small but highly reproducible and could therefore be corrected for. P&T was characterized by a higher reproducibility and smaller isotopic fractionations than SPME. Among the liquid injection techniques, cold on-column injection resulted in slightly better precision compared to split/splitless injection. However, the MDLs determined for liquid injections were 4-6 orders of magnitude higher (i.e., 9.5-2800 mg/L) than for P&T and SPME. Since both of the latter methods are solventless, a better chromatographic resolution was obtained than for the liquid injection techniques. The P&T and SPME methods described here are also applicable for CSIA of D/H ratios, which require 10-20 times higher analyte concentrations than 13 C/ 12 C analysis. Finally, the applicability of the described methods is demonstrated for pollutant concentrations of only 5-60 µg/L in environmental samples.