Stable isotope ratio mass spectrometers

A dual ion beam collector developed by Nier2 is illustrated in Figure 4.1 b. Both collectors are connected to two amplifiers for the simultaneous and direct measurement of ion currents in the dual mode. Amplifier 1 works with degeneration whereas amplifier 2 works without. Such a dual ion beam collector is applied, for example, for precise and accurate measurements of isotope ratios, especially of gases in commercial stable isotope ratio mass spectrometers.2... 

Figure 5.37 Stable isotope ratio mass spectrometer DELTA V from Thermo Fisher Scientific with e beam ion source and multiple ion collection. (Reproduced by permission of Thermo Fisher Scientific, Bremen Germany.)...

Ions formed in an electron ionization mass spectrometer possess a relatively low initial energy spread, therefore single focnsing magnetic sector field instruments are sufficient to separate ion beams with different m/z ratios. Commercial stable isotope ratio mass spectrometers (SIRMS) allow highly precise and accnrate isotope ratio measnrements e.g., with the Finnigan MAT 253, of H/D, C/ C, N/ N, 0/ 0, jQj and SFg) Si/ Si as weU as Ar, Kr and... 

For example, little is known about the isotopic composition of formaldehyde in the atmosphere. Formaldehyde is a chemical intermediate in hydrocarbon oxidation. The carbon (8 C) and hydrogen (8D) isotopic composition of atmospheric formaldehyde is analyzed using continuous flow gas chromatography isotope ratio mass spectrometry." Isotope ratios were measured using GC-IRMS (Finnigan MAT 253 stable isotope ratio mass spectrometer, single-sector field with electron impact ion source and multiple ion collection) with a precision of 1.1 and 50%(lo ) for 8 C and 8D, respectively. The accuracy of the online continuous flow isotope technique was verified by calibrating three aliquots of the gas phase standard via the offline dual inlet IRMS technique. The concentration of formaldehyde in ambient air was determined on IRMS major ion peak areas (i.e., mass 44 for 8 C and mass 2 for 8D)." ... 

Figure 2 Typical electron impact ion source configuration for a stable isotope ratio mass spectrometer.

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... 

Aliquots of CO2 produced during 0-plasmas were analyzed on three different stable isotope-ratio mass spectrometers over a period of five years. The peyote button and the T-shirt label were both run in the summer of 2001. These two samples were chosen to further establish that mass fractionation of carbon during the oxygen plasmas is a small or negligible effect and to test the nondestructive nature of the technique on organic materials. For calibration to Peedee belemnite (PDB) primary standard, carbonate standard NBS-19 (8 C = 1.95%o) was used (i.e., Vienna PDB). values are expressed relative to the V-PDB standard (19). Analytical precision was approximately 0.06%o for 6 C. 

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