Continuous-flow isotope ratio mass spectrometer

The use of carbon isotopes to study DOC is becoming more prevalent due to technological advances in mass spectrometry. DOC generally occurs in natural waters in low concentrations, typically ranging between 0.5 ppm and 10 ppm carbon (Thurman, 1985 see Chapter 5.10). Thus, several liters to tens of liters of water were once necessary to extract enough DOC for conventional dual gas-inlet isotopic analysis. Today, automated total organic carbon analyzers (TOCs) are commercially available, and have been successfully interfaced with continuous flow isotope ratio mass spectrometers (CF-IRMS) for stable isotopic measurements of samples containing ppb concentrations of DOC (e.g., St-Jean, 2003). 

Fessenden, J. E., Cook, C. S., Lott, M. J., and Ehleringer, J. R., Rapid 0 analysis of small water and CO2 samples using a continuous-flow isotope ratio mass spectrometer, Rapid Commun. Mass Spectrom., 16, 1257-1260, 2002. 

Development of Continuous Flow-Isotope Ratio Mass Spectrometers (CE-IRMS) has dramatically facilitated measurement of the ratio of sediment organic matter. 

An intensive research and development is on the way to overcome certain problems coimected to conventional TOC analyzers. As an example, an improved method has been developed [16] for detection of CO2 evolved by heat/acid treatments from different carbon matrices stable C isotope analysis of DIC and DOC species operating on a continuous-flow isotope ratio mass spectrometer (CF-IRMS). According to the authors this technique will allow new and exciting approach for determining carbon both in natural abundance and in organic tracer studies not easily achieved before. To avoid expensive and complicated CO2 detection sensors (e.g., infrared or mass spectrometers), Tue-Ngeun et al. [18] have recently introduced, with a literature review about other... 

Continuous flow-isotope ratio mass spectrometry Gas source mass spectrometry where sample and standard gases are transported using helium as a carrier gas into the mass spectrometer for measurement of isotopic ratios. 

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... 

Continuous Flow Isotope Ratio Monitoring Mass Spectrometers... 

Between the early 1950s, when the dual viscous-flow mass spectrometer was introduced by Nier and the mid 1980s only minor modifications have been made on the hardware of commercial mass spectrometers. Special efforts have been undertaken in the past years to reduce the sample size for isotope measurements. This has led to a modification of the classic dual inlet technique to the continuous-flow isotope ratio monitoring mass spectrometer in which the gas to be analyzed is a trace gas in a stream of carrier gas, which achieves viscous-flow conditions. Today, the majority of gas mass spectrometers are sold with the continuous flow system, instead of the dual inlet system. 

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)." ... 

Studies of 0/ 0 isotope variations in several vascular plant species, mosses and environmental surface bog water from temperate peat bogs (Switzerland) used as climatic archives for paleoclimatic reconstruction were reported by Menot-Combes et 8 0-values in organic material were determined by the online continuous flow method after sample pyrolysis at 1080 °C in the presence of glassy carbon in a Carlo-Erba elemental analyzer. The gases obtained (CO, N2 and H2O) were separated by passing them through a water trap and a GC column in a helium carrier gas. The isotope composition of CO was measured with a VG Prism II isotope ratio mass spectrometer relative to the VSMOW isotope standard. The overall analytical uncertainty is 0.08%o for water 8 0-values." ... 

With the application of the newly developed continuous-flow isotope-ratio monitoring mass spectrometers, the required seawater sample volume for N2O dual isotope measurements have been drastically reduced and therefore facilitated the determination high resolution depth profiles of the N2O dual isotope signature (Brand, 1996 Yoshinari et al, 1997) Repeated measurements of depth profiles at... 

Common name for the area of isotope ratio mass spectrometry for the determination of the stable isotopes of H, N, C, O, S and Si. Compounds containing these elements can be quantitatively converted into simple gases for mass spectrometric isotope ratio analysis, that is, Hj, Nj, CO, CO2, O2, SOj, SiF fed by viscous flow or entrained into a continuous He flow into the ion source of a dedicated isotope ratio mass spectrometer. 

If samples are introduced continuously, then the measurement of isotope ratios can also be continuous as long as sample is flowing into the flame, and several m/z ratios can be examined with almost any kind of mass spectrometer,... 

As the name implies, the sample is introduced into the mass spectrometer as a gas (Nier 1940). There are two types of sources, the classic viscous flow source and the continuous flow source. The viscous flow source typically consists of two identical inlet systems that are coupled to the mass spectrometer by a change-over valve, which allows rapid switching for comparison of isotope ratios measured for sample and standard gases. In the continuous flow source, samples gas is introduced as a bubble in a non-reactive carrier gas stream. 

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