Direct LD-FTMS detection of mineral-associated PAHs and their influence on the detection of co-existing amino acids

Polycyclic aromatic hydrocarbon (PAH) compounds and amino acids (AAs) are both ubiquitous throughout the universe and can be co-located in mineral matrices (e.g., meteorites); therefore, co-detection of PAHs and AAs associated with terrestrial and extra-terrestrial minerals is of interest. Nine PAH compounds representing four chemical classes of PAH (unsubstituted, acetyl-, amino-, and nitro-substituted) were applied onto the surface of quartz, plagioclase, olivine, and ilmenite mineral standards and analyzed using laser desorption/ionization Fourier transform mass spectrometry (LD-FTMS). Mass-to-charge peaks derived from PAH compounds were detected from the surfaces of all minerals evaluated. All PAH compounds were detected in the positive ion mode, whereas only nitro-substituted PAH compounds were detected in negative ion mode. In this and earlier studies, the ability to directly detect mineral-associated AAs by LD-FTMS was dependent on the mineral geomatrix. On iron-bearing minerals AAs appeared as highly fragmented ions in the spectra or were not detectable; however, the addition of the PAH chrysene enabled the ionization and detection of AAs threonine and histidine by LD-FTMS. Thus, for mineral systems such as meteorites, interstellar dust particles, soils, and sediments, the co-detection of AAs associated with PAHs by LD-FTMS is feasible.