Free dicarboxylic and aromatic acids in the carbonaceous chondrites Murchison and Orgueil

Abstract

We have analyzed an important fraction of the free carboxylic acids present in water extracts of the CM2 chondrite Murchison and the CI1 chondrite Orgueil using gas chromatography-mass spectrometry (GC-MS). The free nature of the carboxylic acids analyzed was ensured by employing a single-step water extraction. Analyses revealed the presence of a structurally diverse suite of both aliphatic and aromatic acids in Murchison, while Orgueil exhibits a simpler distribution of exclusively aromatic acids. Within the Murchison aromatic acids, there are previously unreported phthalic acids, methyl phthalic acids, and hydroxybenzoic acids. In Orgueil, benzoic acid and very small amounts of methylbenzoic acids and methylhydroxybenzoic acids were detected. For the aromatic acids in both Murchison and Orgueil, most structural isomers were identified, suggesting an origin by abiotic processes. Quantitative differences are evident between acids in the two meteorites; carboxylic acids are much more abundant in Murchison than in Orgueil. The data suggest that differing levels of aqueous alteration on the meteorite parent body(ies) has produced dissimilar distributions of carboxylic acids.