Quantitative and Compositional Analysis of Trace Amino Acids in Icy Moon Analogues Using a Microcapillary Electrophoresis Laser-Induced Fluorescence Detection System

Abstract

Enceladus’s jet activity, Europa’s putative plume activity, and the evidence supporting global subsurface oceans have made them high-priority targets for future NASA missions. In situ analysis of organic molecules in the jets/plumes or subsurface oceans of these icy moons would provide relevant, detailed information on the formation, habitability, and ongoing planetary processes of celestial bodies and could provide the first evidence of the potential for extant life beyond Earth. Microcapillary electrophoresis with laser-induced fluorescence (μCE-LIF) enables highly-sensitive, automated, quantitative, and compositional analysis of organic molecule monomers and short polymers and can achieve a sub-parts-per-trillion limit of detection. Portable Mars Organic Analyzer prototypes have been built and field-tested, and the Enceladus Organic Analyzer and Microfabricated Organic Analyzer for Biosignatures prototypes are under development as potential instruments for missions to Enceladus or Europa. Here, high-resolution separations of amino acids contained within icy moon analogue solutions of sulfuric acid, carbonic acid, sodium carbonate, and magnesium sulfate were obtained using a benchtop μCE-LIF system. Separations were improved by dilution, pH regulation, and chelation of cations with ethylenediaminetetraacetic acid. Also, a sample taken from Champagne Geyser, a CO2-driven geyser at Chaffin Ranch, Utah, was analyzed for amino acids and found to contain leucine, valine, serine, alanine, and glycine. Alanine and glycine were quantified via a standard curve at 80.1 ± 0.8 μM and 900 ± 100 nM, respectively. This work represents a significant step forward for the liquid-based μCE-LIF analysis of small organic molecules and biopolymers for future space missions to icy bodies like Enceladus and Europa.

A Robust Capillary Electrophoresis with Laser-Induced Fluorescence Detection (CE-LIF) Method for Quantitative Compositional Analysis of Trace Amino Acids in Hypersaline Samples

“…This method is also inherently less prone to electrodispersive effects, as it uses hydrodynamic injection as opposed to electrokinetic injection (see Supporting Information). Although previous CE-LIF analyses have reported a significant deterioration in signal and peak resolution at <5 mM Mg 2+ , we demonstrate that samples with Mg 2+ concentrations of >400 mM can be successfully analyzed for amino acid content using a simple running buffer consisting of only sodium tetraborate.…”

“…Capillary electrophoresis (CE) is a powerful separation technique that offers exceptionally high separation efficiencies, extremely small sample volumes and reagent consumption, and can be coupled to numerous detection systems . When coupled with a laser-induced fluorescence (LIF) detection system, CE can provide sub-nM (or mere attomoles of molecules) limits of detection (LODs). − Multiple amine-reactive fluorophores have been developed, enabling quantitative compositional analysis of ultralow abundance amino acids via CE-LIF . While sample salinity can lead to electro-dispersive effects that reduce resolution and signal, optimization of methodological parameters has been shown to be effective at minimizing the deleterious effects of high salinity. , Multivalent cations are most problematic, as these can alter intercapillary surface chemistries, leading to electroosmotic flow (EOF) inhibition in addition to dispersive effects, resulting in drastically reduced peak resolution, sensitivity, and separation efficiency at cation concentrations as low as 5 mM .…”

“…24 While sample salinity can lead to electrodispersive effects that reduce resolution and signal, optimization of methodological parameters has been shown to be effective at minimizing the deleterious effects of high salinity. 20,23 Multivalent cations are most problematic, as these can alter intercapillary surface chemistries, leading to electroosmotic flow (EOF) inhibition in addition to dispersive effects, 25 resulting in drastically reduced peak resolution, sensitivity, and separation efficiency at cation concentrations as low as 5 mM. 20 The addition of EDTA to the sample has been shown to mitigate these effects, 23 but this adds an additional sample processing step.…”

In situ organic biosignature detection techniques for space applications

“…To avoid or reduce the need for separate desalting steps, a high concentration (30-80 mM) of borate buffer is typically used and further improved by adding EDTA (Stockton et al, 2009a;Creamer et al, 2017). Duca et al (2022) used a 35 mM borate buffer as the background electrolyte, which allowed for a maximum of 1 mM H 2 SO 4 , 10 mM Na 2 CO 2 , and 10 mM MgSO 4 (with 5 mM EDTA) in the injected sample before separation failed when analyzing amino acids. Alternatively, high concentrations of acetic acid (1-5 M) can be used to enable analysis of samples with high ionic strength (Santos et al, 2018;Mora et al, 2022).…”

“…Alternatively, an injector valve can improve repeatability (Zamuruyev et al, 2021). ME, on the other hand, struggles with injection bias that consequently affects the measurement trueness (Duca et al, 2022). Furthermore, the channels often consist of two or more materials that may or may not be fully characterized, ultimately leading to unknown EOF characteristics.…”