[PPS10-03] Organic sulfur compounds and its evolution in carbonaceous meteorites
Keywords:Carbonaceous meteorites, Chemical evolution, Organic sulfur compounds
Recent ultrahigh-resolution mass spectral analysis using Fourier transform-ion cyclotron resonance/mass spectrometry has further identified significantly diverse organo-sulfur homologous compounds consisting of CHOS and CHNOS in elemental compositions from the solvent extracts of the Murchison meteorite . However, chemical evolution of sulfur-bearing organic compounds is not well understood, because the chemical structures of the CHOS and CHNOS compounds have not been clarified. High performance liquid chromatography/high resolution mass spectrometry (HPLC/HRMS) is a powerful tool to deconvolute the occurrence of organic compound mixtures. In the methanol extract of carbonaceous chondrites many CHN compounds were identified as positive ions using HPLC/HRMS , in which homologous series of alkylated pyridines and imidazoles were predominant. organic sulfur compounds are generally observed as a negative ion using electrospray ionization. In this study, we further clarified sulfur-containing compounds in the solvent extracts of carbonaceous chondrites.
Sample and Methods: Three carbonaceous chondrites (Murchison, Allende and Tagish Lake) were powdered using an alumina mortar and pestle in a clean room. The sample powder was sequentially extracted with hexane, dichloromethane (DCM) and methanol (MeOH) by sonication. The DCM and MeOH extracts were analyzed by HPLC/HRMS using an amide column (Inertsil Amide, 1.5 mm i.d. x 25 cm) by hydrophilic interaction liquid chromatography coupled with HRMS using a hybrid quadrupole-Orbitrap MS (Q-Exactive). The eluent was CH3CN/HCOONH4 buffer at a flow rate of 70 mL/min and was electrically charged to 3 kV followed by spraying into MS using electrospray ionization (ESI). The negative ions were collected in full scan mode from m/z 50 to 600 with mass resolution of ~140,000 (m/Dm at m/z 200).
Results and Discussion: Abundant inorganic sulfur oxides and organosulfur compounds were detected in the extracts of the Murchison meteorite within 2 ppm mass precision. Alkylsulfonic acids up to C15 were identified as homologous compounds. The concentration of the sulfonic acid decreased with increasing carbon number, suggesting carbon-chain elongation by step-by-step single carbon addition. The most intense peak was hydroxymethane sulfonic acid (HSA, HOCH2SO3H), which was found in a meteorite for the first time. It is known that HSA is produced by the reaction of formaldehyde with bisulfite (HSO3-) . In previous studies, formaldehyde was quantified in the Murchison meteorite, but the concentration of formaldehyde was less than 10 % of hydroxymethanesulfonic acid in this study [7, 8]. Therefore, most formaldehyde is likely to be consumed by the reaction with bisulfite in the meteorite. The formaldehyde should be abundant prior to the reaction with HSO3- on the meteorite parent body. Because abundant alkylated pyridines (CnH2n-5N) and imidazoles (CnH2n-2N2) detected in the Murchison meteorite could be produced formaldehyde and ammonia , formaldehyde is a common starting material for chemical evolution of primitive asteroids.
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