Ion funnel augmented Mars atmospheric pressure photoionization mass spectrometry for in situ detection of organic molecules

Sweep Jet Collection Laser-Induced Acoustic Desorption Atmospheric Pressure Photoionization for Lipid Analysis Applications

Laser-induced acoustic desorption coupled to microplasma-based atmospheric pressure photoionization (LIAD-APPI) using a nebulized sweep jet to aid in dopant introduction and ion transmission has been applied to the analysis of model, apolar lipid compounds. Specifically, several sterols, sterol esters, and triacylglycerols were detected using dopants such as anisole and toluene. Additionally, several triacylglycerols, sterols, carboxylic acids, and hopanoids were detected from complex mixtures of olive oil and Australian shale rock extract as a first demonstration of the applicability of LIAD-APPI on real-world samples. Detection limits using a sweep jet configuration for α-tocopherol and cholesterol were found to be 609 ± 61 and 292 ± 29 fmol, respectively. For sterol esters and triacylglycerols with a large number of double bonds in the fatty acid chain, LIAD-APPI was shown to yield greater molecular ion or [M+NH₄]⁺ abundances than those with saturated fatty acid chains. Dopants such as anisole and toluene, with ionization potentials (IPs) of 8.2 and 8.8 eV, respectively, were tested. A greater degree of fragmentation with several of the more labile test compounds was observed using toluene. Overall, LIAD-APPI with a nebulized sweep jet requires minimal sample preparation and is a generally useful and sensitive analysis technique for low-polarity mixtures of relevance to biochemical assays and geochemical profiling. Graphical Abstract.

Laser-Induced Acoustic Desorption Atmospheric Pressure Photoionization via VUV-Generating Microplasmas

We demonstrate the first application of laser-induced acoustic desorption (LIAD) and atmospheric pressure photoionization (APPI) as a mass spectrometric method for detecting low-polarity organics. This was accomplished using a Lyman-α (10.2 eV) photon generating microhollow cathode discharge (MHCD) microplasma photon source in conjunction with the addition of a gas-phase molecular dopant. This combination provided a soft desorption and a relatively soft ionization technique. Selected compounds analyzed include α-tocopherol, perylene, cholesterol, phenanthrene, phylloquinone, and squalene. Detectable surface concentrations as low as a few pmol per spot sampled were achievable using test molecules. The combination of LIAD and APPI provided a soft desorption and ionization technique that can allow detection of labile, low-polarity, structurally complex molecules over a wide mass range with minimal fragmentation. Graphical Abstract ᅟ.

Supercritical Carbon Dioxide Extraction of Coronene in the Presence of Perchlorate for In Situ Chemical Analysis of Martian Regolith

The analysis of the organic compounds present in the martian regolith is essential for understanding the history and habitability of Mars, as well as studying the signs of possible extant or extinct life. To date, pyrolysis, the only technique that has been used to extract organic compounds from the martian regolith, has not enabled the detection of unaltered native martian organics. The elevated temperatures required for pyrolysis extraction can cause native martian organics to react with perchlorate salts in the regolith and possibly result in the chlorohydrocarbons that have been detected by in situ instruments. Supercritical carbon dioxide (SCCO2) extraction is an alternative to pyrolysis that may be capable of delivering unaltered native organic species to an in situ detector. In this study, we report the SCCO2 extraction of unaltered coronene, a representative polycyclic aromatic hydrocarbon (PAH), from martian regolith simulants, in the presence of 3 parts per thousand (ppth) sodium perchlorate. PAHs are a class of nonpolar molecules of astrobiological interest and are delivered to the martian surface by meteoritic infall. We also determined that the extraction efficiency of coronene was unaffected by the presence of perchlorate on the regolith simulant, and that no sodium perchlorate was extracted by SCCO2. This indicates that SCCO2 extraction can provide de-salted samples that could be directly delivered to a variety of in situ detectors. SCCO2 was also used to extract trace native fluorescent organic compounds from the martian regolith simulant JSC Mars-1, providing further evidence that SCCO2 extraction may provide an alternative to pyrolysis to enable the delivery of unaltered native organic compounds to an in situ detector on a future Mars rover.

KEY WORDS

Biomarkers-Carbon dioxide-In situ measurement-Mars-Search for Mars' organics. Astrobiology 16, 703-714.

Plasma ionization under simulated ambient Mars conditions for quantification of methane by mass spectrometry

Ambient ionization techniques enable ion production in the native sample environment for mass spectrometry, without a need for sample preparation or separation. These techniques provide superior advantages over conventional ionization methods and are well developed and investigated for various analytical applications. However, employing ambient ionization techniques for in situ extra-terrestrial chemical analysis requires these techniques to be designed and developed according to the ambient conditions of extra-terrestrial environments, which substantially differ from the ambient conditions of Earth. Here, we report a plasma ionization source produced under simulated ambient Mars conditions for mass spectrometry. The plasma ionization source was coupled to a quadrupole mass spectrometer, and quantitative and qualitative analyses of trace amounts of methane, as an analyte of interest in Mars discovery missions, were demonstrated. The miniature plasma source was operational at a net power as low as ∼1.7 W in the pressure range of 4-16 Torr. A detection limit as low as ∼0.15 ppm (v/v) at 16 Torr for methane was demonstrated.

Detection of trace organics in Mars analog samples containing perchlorate by laser desorption/ionization mass spectrometry

Evidence from recent Mars missions indicates the presence of perchlorate salts up to 1 wt % level in the near-surface materials. Mixed perchlorates and other oxychlorine species may complicate the detection of organic molecules in bulk martian samples when using pyrolysis techniques. To address this analytical challenge, we report here results of laboratory measurements with laser desorption mass spectrometry, including analyses performed on both commercial and Mars Organic Molecule Analyzer (MOMA) breadboard instruments. We demonstrate that the detection of nonvolatile organics in selected spiked mineral-matrix materials by laser desorption/ionization (LDI) mass spectrometry is not inhibited by the presence of up to 1 wt % perchlorate salt. The organics in the sample are not significantly degraded or combusted in the LDI process, and the parent molecular ion is retained in the mass spectrum. The LDI technique provides distinct potential benefits for the detection of organics in situ on the martian surface and has the potential to aid in the search for signs of life on Mars.