Here, we present a new application of desorption electrospray
ionization
(DESI) and laser ablation electrospray ionization (LAESI) mass spectrometry
imaging to assess the spatial location of organic compounds, both
polar and nonpolar, directly from rock surfaces. Three carbonaceous
rocks collected from an aquatic environment and a berea sandstone
subjected to a small-scale oil recovery experiment were analyzed by
DESI and LAESI. No rock pretreatment was required before DESI and
LAESI analyses. DESI detected and spatially mapped several fatty acids
and a disaccharide on the surfaces of carbonaceous rocks, and various
nitrogenated and oxygenated compounds on the surfaces of berea sandstone.
In contrast, LAESI using a 3.4 μm infrared laser beam was able
to detect and map hydrocarbons on the surfaces of all rock samples.
Both techniques can be combined to analyze polar and nonpolar compounds.
DESI can be used first to detect polar compounds, as it does not destroy
the rock surface, and LAESI can then be used to analyze nonpolar analytes,
as it destroys a layer of the sample surface. Both techniques have
the potential to be used in several scientific areas involving rocks
and minerals, such as in the analysis of industry-derived contaminants
in aquatic sediments or in small-scale rock–fluid interaction
experiments.
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