Analyses of Aliphatic Aldehydes and Ketones in Carbonaceous Chondrites

Aliphatic
aldehydes and ketones are essential building blocks for
the synthesis of more complex organic compounds. Despite their potentially
key role as precursors of astrobiologically important molecules, such
as amino acids and carboxylic acids, this family of compounds has
scarcely been evaluated in carbonaceous chondrites. The paucity of
such analyses likely derives from the low concentration of aldehydes
and ketones in the meteorites and from the currently used chromatographic
methodologies that have not been optimized for meteorite analysis.
In this work, we report the development of a novel analytical method
to quantify the molecular distribution and compound-specific isotopic
analysis of 29 aliphatic aldehydes and ketones. Using this method,
we have investigated the molecular distribution and 13C-isotopic
composition of aldehydes and ketones in 10 carbonaceous chondrites
from the CI, CM, CR, and CV groups. The total concentration of carbonyl
compounds ranged from 130 to 1000 nmol g–1 of meteorite
with formaldehyde, acetaldehyde, and acetone being the most abundant
species in all investigated samples. The 13C-isotopic values
ranged from −67 to +64‰ and we did not observe clear
relationships between 13C-content and molecular weight.
Accurately measuring the relative abundances, determining the molecular
distribution, and isotopic composition of chondritic organic compounds
is central in assessing both their formation chemistry and synthetic
relationships.