irm-EAMS (δ13C and δ15N)
CO2 in-air (δ13C and δ18O)
O2/N2 in air (+ δ18O of O2 in air or Ar/N2)
Laser Ablation
GasBench
TC/EA ('Pyrolysis', δ2H and δ18O)
Acid reaction and air mixing system (ARAMIS) (δ13C and δ18O)
TC/EA ('Pyrolysis', δ2H and δ18O)
δ2H and δ18O determination from organic material and from water
Since commissioning our 252 mass spectrometer to high precision CO2-in-air isotope measurements the number of water samples, analysed on this machine until 2000, has ceased. There have, however, been repeated requests in the institute to start with δ2H and δ18O determination of water samples again. Hence, following the move of the institute to the new building, we began an evaluation of the high temperature pyrolysis technique (TC/EA) for this purpose. One advantage of the technique is that it will allow δ2H and δ18O determinations to be made from the same vial with the same analytical setup. However, initial experiments showed that precision for δ18O was between 0.15‰ and 0.3‰. This must be improved before routine measurements can be started.
The TC/EA is capable of determining δ18O of organic material without prior conversion of the sample to H2O or other time consuming reactions. In a recent publication (K Revesz and JK Böhlke, Anal. Chem. 74, 2002, 5410) it was clearly shown that the 'classical' techniques for δ18O preparation from organic material suffer from more or less severe contamination due to isotope exchange of oxygen with quartz. The high temperature pyrolysis seems to become the new gold standard for this type of analysis.
Water can be analysed using this system by injecting the sample directly through a septum. Enclosing water in a silver capsule for concurrent determination with organic bulk material, however, is tedious and difficult to handle in a routine fashion. Because the only reliable international reference materials are water (VSMOW, VSLAP, GISP), there is an urgent need for a pair of oxygen containing organic compounds with a large difference in isotopic content. We therefore proposed to use benzoic acid to the IAEA. Together with A. Schimmelmann (Univ. Indiana Bloomington) and with financial support from the IAEA (for A.S.) we engaged in the fabrication of a pair of benzoic acids, one with a natural δ18O-value, and the other one slighly enriched. For producing the latter, we sought the collaboration of the Institute of Inorganic Chemistry at the University in Jena. In a process involving δ18O enriched water and reaction at 90°C at pH=0, which lasted for more than two weeks, the enriched δ18O benzoic acid was generated. After cleaning, drying and homogenizing, the isotope values were measured in our lab using the TC/EA setup. Some of the material was sent to Bloomington for a parallel determination using lower temperature decarboxylation. The results of both laboratories were very close at about +23‰ and +71‰ vs. VSMOW with an offset of about 0.5‰. The material was sent to the IAEA in Vienna for further evaluation and for organizing a wider ring test.
We have improved the precision of our water analysis for both, δ2H and δ18O, to a level, that it can rival the classical preparation (reduction with U or Cr and equilibration). The method has been published as M. Gehre, H. Geilmann, J. Richter, R.A. Werner, and W.A. Brand, Continuous Flow 2H/1H and 18O/16O Analysis of Water Samples with Dual Inlet Precision Rapid Comm. Mass Spectrom. (2004) 18: 2650 - 2660.
In this paper, post run evaluation sheets for converting raw measured data to final data on the VSMOW/Slap scale are described and mentioned. Corrections are made for drift, sample-to-sample memory, and scale contraction. Examples for oxygen and hydrogen can be downloaded: Water_Spreadsheet_CO and Water_Spreadsheet_DH
