Reexamination of the Effect of Pyridine Treatment on Phase Q in Orgueil

Introduction:Most of the primordial noble gases in meteorites are trapped in a poorly characterized carbonaceous carrier named " phase Q ". Marrocchi et al. [1] reported that the HF/HCl residue of Orgueil (CI) lost the low temperature fractions of heavy noble gases (36 Ar, 84 Kr and 132 Xe) in phase Q upon pyri-dine treatment. As pyridine is known to induce the swelling of the macromolecular network of organic matter, their result indicates that the low temperature phase Q is macromolecular organic carbon.However, Busemann et al. [2] showed that pyridine had no significant effect on the noble gas contents of HF/HCl residuesofMurchison (CM2), Bells (C2 ungrouped), EET92042(CR2) and GRO95577 (CR1). Thus we prepared the HF/HCl residue of Orgueiland its pyri-dine-treated sample, and reexamined the results ofMarrocchi et al. [1].We measured the elemental abundances and isotopic compositions of all noble gases bystepwise-heatingmethod with five temperature steps. Sample Preparation:A 1.2602g aliquot of Orgueil was dissolved with HF/HCl.The obtained original HF/HCl residue was 43.4mg. Eleven percent of the original HF/HCl residue was further treated with fresh pyridine for two days at room temperature .The noble gas measurements were carried out with the mass spectrometer VG5400 installed at Osaka University. Results and Discussion:Our obtained elemental concentrations of noble gasesof the original HF/HCl residue are slightly low compared to those of Marrocchi et al. [1] and Huss et al. [3]. These latter two data sets show very identical 36 Ar, 84 Kr and 132 Xe concentrations and Xe isotopic ratios.The total elemental abun-dancesof noble gases of our pyridine-treated residuewere slightly higher than those of Morrocchi et al. [1], but confirmed that pyri-dine treatment surely decreased the noble gas concentrations in the original HF/HCl residue. The lost fractionsof the individual noble gases from the original HF/HCl residue were 21% (