Analysis of Monocarboxylic Acids in the Murchison Meteorite by Sequential Extraction

Abstract

Monocarboxylic acids (MCAs) in meteorites have significant potential to provide insight into the evolution of organic matter in the solar system considering their abundance and ubiquity. Using the Murchison meteorite, we developed a method to analyze the molecular distribution and carbon isotope ratios of MCAs in the various chemical forms in which they are present. The MCAs were divided into four fractions (F1, F2-1, F2-2, and F3) using different extraction techniques and solvents. F1 was obtained by ultrasonic extraction with CH₃OH, F2-1 by ultrasonic extraction with H₂O, F2-2 by reflux extraction with H₂O, and F3 by reflux extraction with KOH/CH₃OH. The four fractions contained linear C2–C6 and branched C4–C6MCAs, and the molecular distribution of MCAs was similar for F2-1, F2-2, and F3. The average total abundance of fractions F1, F2-1, F2-2, and F3 was 12.2, 7.06, 3.95, and 0.849 μmol g^–1 of meteorite, respectively. The carbon isotope ratios of F1 and F2-1 + F2-2 were measured, and the δ¹³C values of MCAs in F2-1 + F2-2 appeared slightly ¹³C-enriched compared with those in F1 for each counterpart. Furthermore, inorganic ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^–, and SO₄^2– were detected by ion chromatography. Analysis of the molecular distribution and isotopic ratios of MCAs in meteorites, based on their chemical form, can provide the relation between MCAs and insoluble organic matter (IOM), the behavior of MCAs during aqueous alteration in the parent body, and the contribution of MCAs to the missing carbon, which is lost during IOM isolation.