Exploring Biosignatures Associated with Thenardite by Geomatrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (GALDI-FTICR-MS)

Abstract

Geomatrix-assisted laser desorption/ionization (GALDI) in conjunction with a Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) has been employed to determine how effectively bio/organic molecules associated with the mineral thenardite (Na ₂ SO ₄ ) can be detected. GALDI is based on the ability of the mineral host to assist desorption and ionization of bio/organic molecules without additional sample preparation. When glycine was mixed with thenardite, glycine was deprotonated to produce C ₂ H ₄ NO ₂ ⁻ at m/z 74.025. The combination of stearic acid with thenardite produced a complex cluster ion at m/z 390.258 in the negative mode, which was assigned a composition of C ₁₈ H ₃₉ O ₇ Na⁻. A natural sample of thenardite from Searles Lake in California also produced a peak at m/z 390.260. The bio/organic signatures in both the laboratory-based and natural samples were heterogeneously dispersed as revealed by chemical imaging. The detection limits for the stearic acid and thenardite combination were estimated to be 3 parts per trillion or ∼7 zeptomoles (10 ^{− 21} ) per laser spot. Attempts to improve the signal-to-noise ratio by co-adding FTICR-MS data predetermined to contain the biosignatures of interest revealed problems due to a lack of phase coherence between data sets.

Keywords:

• Glycine
• stearic acid
• geomatrix
• evaporite
• GALDI
• laser desorption
• mass spectrometry
• FTICR-MS

Acknowledgments

The authors acknowledge support by the National Aeronautics and Space Agency (NASA) Exobiology Program (EXB03-0000-0054). CDR would also like to thank Inland Northwest Research Alliance (INRA) and Montana Space Grant Consortium for support. Research was performed at the Idaho National Laboratory under DOE/NE Idaho Operations Office Contract DEAC0705ID14517.