Deuterium exchange during acid-demineralisation

Area of Science:

• Astrochemistry
• Isotope Geochemistry
• Meteoritics

Background:

• The Murchison meteorite contains abundant insoluble organic matter with significant deuterium (D) enrichment.
• Understanding the origins of this D-enrichment requires precise isotopic analysis of meteoritic components.
• Demineralisation using deuterated (D-labelled) reagents is a common method for preparing samples.

Purpose of the Study:

• To investigate potential hydrogen (H)-isotope exchange between meteorite residues and D-labelled reagents during sample preparation.
• To quantify the extent of this exchange and assess its impact on previous isotopic analyses of meteoritic organic matter.

Main Methods:

• Isotopic analysis of residues from the Murchison meteorite after demineralisation.
• Use of D-labelled reagents (e.g., H2O) during the demineralisation process.
• Analysis of pyrolysable hydrogen (H) released as water (H2O).

Main Results:

• Measurable H-isotope exchange occurred between the meteorite organic residues and the D-labelled reagents.
• The extent of exchange was estimated to be 3-5% of the total H pyrolysable as H2O.
• Significant inhomogeneity of the meteoritic organic matter prevented precise quantification of the exchange.

Conclusions:

• The observed H-isotope exchange could influence the shape of D-release curves as a function of temperature.
• Despite the exchange, the overall conclusions regarding the bulk D-enrichment of insoluble meteoritic organic matter remain valid.
• Further studies are needed to refine methods for accurate isotopic analysis of extraterrestrial organic matter.