Analytical Characterization Approaches to Measure Prebiotically Relevant Compounds in High Salinity Impact-Induced Hydrothermal Systems

Experiments exploring potential emergence-of-life chemistry in a laboratory setting critically depend on simulating realistic early-Earth environments. Such experimental conditions include the implementation of controlled high temperatures and pressures, anoxic gas phases, saline fluids, and diverse mixtures of low-concentration organic compounds. Common analytical methods, such as mass spectrometry (MS) and gas chromatography (GC), often require desalting and derivatization processing steps prior to analysis. These preprocessing steps often require additional time, materials, and/or equipment and are not always amenable to nontargeted analyses or detection of low concentrations of organic compounds in complex mixtures. Here, we explore the use of two direct-analysis methods to measure simple organic molecules in highly saline aqueous solutions (ca. 0.5 M), which were likely present in seawater-associated early-Earth environments. Specifically, Direct Analysis in Real Time (DART)-MS and NMR spectroscopy were used as independent analyses with minimal sample processing to detect and identify glycine, glycolic acid, acetone, acetic acid, propionic acid, methylsulfonic acid, and methylbutanoic acid. Such small soluble organic compounds could have been found in concentrations below 100 μM on early Earth. The performance of each analytical method was assessed, and it was found that they can be used in conjunction to obtain semiquantitative information about each analyte of interest. Additionally, the same techniques were applied to the analysis of a hydrothermally altered sample subjected to 150 °C and 500 bar. Results show that DART-MS and NMR have the potential to help interrogate complex samples through untargeted analyses.