ABSTRACT
We have developed a new inlet system for a gas sample isotope ratio mass spectrometer (IRMS). It is based on the well-known open split design from the gas chromatography/mass spectrometry (GC/MS) system due to its simplicity. The advantages over the conventional double inlet system with the metal bellows design include an improved reproducibility mainly due to a highly controllable pressure and temperature adjustment, a markedly lowered memory effect due to an uninterrupted gas flow through the ion source which limits adsorption/desorption processes on surfaces, and a single inlet capillary circumventing problems of asymmetrical behavior of sample and reference inlet paths. Furthermore, sample consumption is of the same order as for conventional measurements (i.e. about 0.4 mmol per hour), of which however only 2 &mgr;mol/h is used for the actual isotope ratio determination since the major gas amount acts as a gas flow seal against the atmosphere, corresponding to a 100-200 fold overkill. This may be improved in future systems. Copyright 2000 John Wiley & Sons, Ltd.
ABSTRACT
A new technique for measuring CO(2) concentration in air samples, based on mass spectrometry, is described as an alternative to the common gas chromatographic method. Using a dual inlet isotope ratio mass spectrometer (IRMS), the ratio of the abundances of the m/z peaks 44 and 28 is determined. The precision of measurements (standard deviation <3 ppmv) is generally as good as the analysis with gas chromatography for small air samples (<1 ml STP of air). A major advantage of this new method is the possibility of parallel elemental and isotopic measurements of many air components. The technique is further improved by new wide mass range mass spectrometers allowing simultaneous intensity measurements of several m/z values between 28 and 44, resulting in an uncertainty of <0.5 ppm. The precision is somewhat limited by the production of N(2)O and NO(2) from N(2) and O(2) in the ion source, which accounts for about half of the signal strength at m/z 44. Copyright 2000 John Wiley & Sons, Ltd.
