10:45 AM - 12:15 PM
[PPS08-P12] TOF-SIMS analysis of organic matter in Ryugu samples.
Keywords:asteroid Ryugu, organic matter, TOF-SIMS
Introduction: The Hayabusa2 spacecraft returned samples from surface of asteroid Ryugu were investigated by the Hayabusa2 initial analysis team from June 2021 to May 2022. The initial analysis organic macromolecule team has performed chemical, molecular, and isotopic analysis on the intact Ryugu grains and insoluble organic matter (IOM) isolated from Ryugu samples by for example μ-FTIR, micro-Raman spectroscopy, STXM-XANES, STEM-EELS, AFM-IR, and NanoSIMS [1].
Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is useful to analyze the molecular species present on the sample surface. In this study, we conducted in-situ analysis on bulk Ryugu samples and the isolated IOM using TOF-SIMS to investigate the chemical structure of macromolecular organic matter in asteroid Ryugu.
Experimental: IOM were extracted from two Ryugu aggregate samples (A0106 and C0107) with 6M HCl and 1M HCl/9M HF at Hiroshima University [1]. Those Ryugu IOM samples and intact Ryugu grains A0106 and C0057 were used in this study. For comparison, Tagish Lake IOM and bulk samples of Tagish Lake were used. The lithology of Tagish Lake used in this study has a lower proportion of chondrules and framboidal magnetite in the matrix, which show similar as the alteration degree of the 11i specimen reported by the previous study [2]. All those samples were pressed onto clean Cu disks (~ 2.1 mmφ, t = 0.05 mm) and mounted in in-house SUS holder for TOF-SIMS analysis. Roughness of the sample surface and Cu disks were < 10 µm for fragment samples, < 5 µ m for IOM samples, respectively. The TOF-SIMS measurement was performed using a TRIFT III spectrometer (ULVAC-PHI, Inc., Chigasaki, Kanagawa, Japan) at Nagoya University. Positive and negative ion spectra were obtained using Au+ gold primary ion (22 keV, 2.6 nA, ~1 µmφ). The measured surface areas were 200 × 200 μm and acquisition time of about 5 min for each sample. The ion intensity of each species was obtained from region of interest (ROI) of the sample of all samples and were normalized by using total ion intensity of signals at m/z 0 to 150.
Results and Discussion: In the positive ion spectra (m/z 0-150) obtained from all samples, a variety of fragment ions such as Cn+, CnHx+, CnHxNy+, CnHxOz+, CnHxNyOz+, HxNy+ were observed.
The ionic species with the largest total ion intensities are the CnHx+ ions (n=1~11), which are derived from both aromatic and aliphatic compounds [e.g., 3]. The difference in CnH2+ intensities [3] indicates that the Tagish Lake meteorite IOM is more aromatic than the Ryugu IOM. This result may indicate the Tagish Lake sample in this study have been more strongly affected by aqueous alteration in the parent body than the Ryugu sample [4], or reflects the difference of meteorite sample and the surface of asteroid Ryugu. On the other hand, CnHx+ ions the IOM samples showed no similar trend obtained from the bulk samples. For CnHxNy+ ions, C3H8N+ fragment ions were the most intense in the bulk sample for both the Ryuguu and Tagish lake meteorites. The CnHxOz+ ions also showed the same result as in the bulk samples, with the C2H3O+ and C5H3O+ ions having the highest intensities in the bulk samples of both Ryugu samples and Tagish Lake meteorite. For IOM samples, while the Tagish Lake meteorite IOM shows a similar trend to the bulk sample, the Ryugu IOM shows a large intensity of other species (C5H3O+ and C3H3O+). These results indicate a difference in chemical structure between the organic matter present in the bulk sample and the IOM. This would suggest that the structure of the organic matter in the Ryugu sample is more easily modified, which may due to their more pristine feature.
References:
[1] Yabuta H. et al. (2023) Science. [2] Herd et al. (2011) Science, 332, 1304.[3] Sjövall P et al. (2021) Fuel, 286, 119373. [4] Vinogradoff et al. (2017) Geochimica et Cosmochimica Acta 212, 234.
Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is useful to analyze the molecular species present on the sample surface. In this study, we conducted in-situ analysis on bulk Ryugu samples and the isolated IOM using TOF-SIMS to investigate the chemical structure of macromolecular organic matter in asteroid Ryugu.
Experimental: IOM were extracted from two Ryugu aggregate samples (A0106 and C0107) with 6M HCl and 1M HCl/9M HF at Hiroshima University [1]. Those Ryugu IOM samples and intact Ryugu grains A0106 and C0057 were used in this study. For comparison, Tagish Lake IOM and bulk samples of Tagish Lake were used. The lithology of Tagish Lake used in this study has a lower proportion of chondrules and framboidal magnetite in the matrix, which show similar as the alteration degree of the 11i specimen reported by the previous study [2]. All those samples were pressed onto clean Cu disks (~ 2.1 mmφ, t = 0.05 mm) and mounted in in-house SUS holder for TOF-SIMS analysis. Roughness of the sample surface and Cu disks were < 10 µm for fragment samples, < 5 µ m for IOM samples, respectively. The TOF-SIMS measurement was performed using a TRIFT III spectrometer (ULVAC-PHI, Inc., Chigasaki, Kanagawa, Japan) at Nagoya University. Positive and negative ion spectra were obtained using Au+ gold primary ion (22 keV, 2.6 nA, ~1 µmφ). The measured surface areas were 200 × 200 μm and acquisition time of about 5 min for each sample. The ion intensity of each species was obtained from region of interest (ROI) of the sample of all samples and were normalized by using total ion intensity of signals at m/z 0 to 150.
Results and Discussion: In the positive ion spectra (m/z 0-150) obtained from all samples, a variety of fragment ions such as Cn+, CnHx+, CnHxNy+, CnHxOz+, CnHxNyOz+, HxNy+ were observed.
The ionic species with the largest total ion intensities are the CnHx+ ions (n=1~11), which are derived from both aromatic and aliphatic compounds [e.g., 3]. The difference in CnH2+ intensities [3] indicates that the Tagish Lake meteorite IOM is more aromatic than the Ryugu IOM. This result may indicate the Tagish Lake sample in this study have been more strongly affected by aqueous alteration in the parent body than the Ryugu sample [4], or reflects the difference of meteorite sample and the surface of asteroid Ryugu. On the other hand, CnHx+ ions the IOM samples showed no similar trend obtained from the bulk samples. For CnHxNy+ ions, C3H8N+ fragment ions were the most intense in the bulk sample for both the Ryuguu and Tagish lake meteorites. The CnHxOz+ ions also showed the same result as in the bulk samples, with the C2H3O+ and C5H3O+ ions having the highest intensities in the bulk samples of both Ryugu samples and Tagish Lake meteorite. For IOM samples, while the Tagish Lake meteorite IOM shows a similar trend to the bulk sample, the Ryugu IOM shows a large intensity of other species (C5H3O+ and C3H3O+). These results indicate a difference in chemical structure between the organic matter present in the bulk sample and the IOM. This would suggest that the structure of the organic matter in the Ryugu sample is more easily modified, which may due to their more pristine feature.
References:
[1] Yabuta H. et al. (2023) Science. [2] Herd et al. (2011) Science, 332, 1304.[3] Sjövall P et al. (2021) Fuel, 286, 119373. [4] Vinogradoff et al. (2017) Geochimica et Cosmochimica Acta 212, 234.