Investigating Photochemical Effects of Micro-XRF Analysis on Common Geochemical Compounds

Chemical alteration of organic compounds exposed to X-rays from portable micro-focus X-ray fluorescence instruments is a potential concern for many applications (e.g. the analysis of valuable works of art, planetary lander and rover missionsfocused on astrobiology, etc.). We performed a preliminary study ofthe effects of intense and prolonged exposure to X-ray radiation from a micro-focus XRF instrument onthe chemical composition of two organic compounds representative of molecules commonly reported from the terrestrial rock record. Pyrene, a polycyclic aromatic hydrocarbon (PAH), and palmitic acid, a saturated fatty acid, were deposited in glass vials and irradiated for 90 and 24 hours, respectively. Radiation was delivered using a Bruker ARTAX instrument fitted with a polycapillary focusing optic and Rh anode X-ray tube operated at 50 kV/0.6 mA. Controls and samples were compared for chemical alteration by Gas Chromatography/Mass Spectrometry (GC-MS) and Raman spectroscopy,beforeandafter exposure to the X-ray beam. No indication of chemical alteration of the compounds was detected by GC-MS orRaman spectroscopy. A color change that was observed in the vials containing the samples after X-ray irradiation was likely caused by reversible activation of color centers in the borosilicate glass vials