Compound-specific isotope ratio mass

GC-C-IRMS The combination of a gas chromatograph with a combustion cell and an isotope ratio mass spectrometer allows the determination of compound-specific isotope ratios, which for some compound classes such as the nucleobases is the only method to determine whether they are indigenous to the meteorite or terrestrial contamination (J). 

Compound specific stable isotope analysis using gas chromatography combined with an isotope ratio mass spectrometer - GC-IRMS (see also Chapter 7) - is now a mature analytical technique in environmental science and technology, especially in the area of contaminant source attribution and in assessing the biodegradation of contaminants.108 Several studies have focused on 13C/12C, 180/160 and 170/160 isotope ratio measurements for volatile organic and metalor-ganic compounds to study isotope fractionation effects and to identify contamination in the environment.109... 

Carbon isotope fractionation effects of individual compounds were observed in living organisms and also as a result of enzymatic isotope effects and reaction kinetics in biological systems. Such fractionation effects have to be examined by isotope ratio mass spectrometry in order to understand specific processes in life sciences or in environment.75... 

Stable isotope ratio mass spectrometers that interface directly to a gas chromatograph are commercially available. This type of analysis is known variously as gas chromatography-isotope ratio mass spectrometry (GC-IRMS), gas chromatography-combustion isotope ratio mass spectrometry, or compound-specific isotope analysis. The same principle of operation has also been used for more general isotope ratio analyses, where the components of interest are combusted as bulk samples. This type of arrangement, known as continuous flow-isotope ratio mass spectrometry, allows rapid automated analyses of and... 

The carbon isotopic composition of individual compounds in gases, oUs, condensates, and source rock extracts is measured by GC-combustion-isotope ratio MS (GC-C-IRMS) or isotope ratio monitoring GC-MS (irm-GC-MS). This is a specifically designed capillary GC MS system in which hydrocarbon components from the GC effluent are combusted to carbon dioxide (CO2) and water (H2O). The CO2 of combustion is continuously analyzed on-line by a triplecollector isotope-ratio mass spectrometer to provide precise ratio mea-... 

It should be mentioned that the same kind of equations hold if stable isotopes are applied for labelling of the elements or compounds to be determined by isotope dilution analysis. In this application, isotope ratios are taking the place of specific activities and they are preferably measured by mass spectrometry. 

The determination of differences in isotopic ratios requires very precise measurements. The combustion step for the sample preparation is usually carried out immediately prior to the injection into the MS. There exist instruments which associate in line a gas chromatograph, a tubular combustion oven, containing copper oxide heated to 800 °C, and a low-resolution MS equipped with several Faraday detectors, each collecting the signal corresponding to a specific mass. A calibration compound is co-injected with the product to be studied. 

---