2P-15 PDF
Development of a Continuous Flow Isotope Ratio Mass Spectrometer for Stable Oxygen Isotope Analysis of Solid Samples
A high temperature furnace system was newly installed for a He continuous flow isotope ratio mass spectrometer (CF-IR-MS) for the analysis of oxygen stable isotope compositions in solid samples, especially those of phosphate and silicate, whose isotope compositions are currently difficult to determine. A tungsten vessel placed in a vacuum chamber is used as a reaction crucible where oxygen in the solid sample is converted to carbon monoxide. This vessel can be heated up to 2000oC by the surrounding Ta filament. The produced carbon monoxide flows into the mass spectrometer with a continuous He stream and is used for determination of the oxygen isotope ratio. The phosphate oxygen can be converted completely into carbon monoxide at more than 1600oC, although its conversion rate was less than 90% at 1300oC, which is the maximum temperature for commercial products. The imperfect conversion affects the analytical results, as this causes isotopic fractionation between the converted and residual oxygen and intersample memory effects (i.e., contamination of the oxygen from the sample being analyzed with oxygen that was not converted to CO during the previous analyses). The installation of this new furnace system resulted in high precision analyses.