Automated Lander Planetary Analog Composition Analyzer (ALPACA)

            The Automated Lander Planetary Analog Composition Analyzer (ALPACA) is a chemical and organic composition analyzer well suited for future landed missions to ocean worlds such as Enceladus, Europa, and Titan. ALPACA utilizes the Biosignature Preparation for Ocean Worlds (BioPOW) instrument for sample enrichment (concentrating the sample) and purification to enable detections in challenging ocean world environments [1]. The BioPOW system performs the following operations: 1) melt an icy sample; 2) purify amino acids, and other organics, from salts and inorganic compounds [2]; 3) concentrate and derivatize targeted amino acids for downstream GC analyses (Figure 1). The downstream GC analyses are accomplished with a micro-electromechanical system gas chromatograph (μ-GC) [3–5]. The ALPACA instrument is being developed under NASA’s Planetary Science and Technology Through Analog Research (PSTAR) program (NASA Grant 80NSSC25K7720).

            The automated, on-chip BioPOW system receives an icy sample in a sample cup that was specifically designed to interface with the CADMES arm described in NASA’s ICEE-2 program. Sample cup testing demonstrated repeatability and reliability for melting icy samples with steady heating to 100 °C in ~350 seconds using embedded nichrome wire. Once melted, fluid is transferred to the cation exchange module (ion exchange chromatography column) that is referred to as the Wet Lab of the BioPOW system. For purification and concentration of amino acids, the following steps are performed: 1) Use 10 mM hydrochloric acid (HCl) to de-protonate the resin (cation exchange beads) and provide an overall negative charge; 2) acidified sample (4OH) elutes the amino acids from the resin for subsequent derivatization and analysis (Figure 2). The eluted amino acids are moved to the second portion of the BioPOW Wet Lab, the derivatization chamber. The eluted sample is dried (60 °C until powder) and derivatized with MTBSTFA (90 °C for 1 hour) using the custom-built derivatization chamber. The derivatization chamber has three ports, one for inserting the sample and MTBSTFA, another for carrier gas, and one output which is used for water-vapor exhaust during the drying stage and for delivering the derivatized amino acid vapor to the μ-GC. Metal microfluidic tubing connects the chamber to input sources and output for the high temperatures required during derivatization. Minco® heater elements wrapped around the chamber provide the heat source.

            The μ-GC utilizes silicon chip-based technology for miniaturization and consists of three main parts: 1) preconcentrator; 2) separation column; and 3) detectors. The preconcentrator is made from deep-reactive ion etching (DRIE) of silicon wafers for μ-channel ports for carbon molecular sieve (bead) loading, sample loading (preconcentration), carrier gas and vacuum pump connection, and outlet connection to the μ-GC separation column (μ-column). The molecular sieve material is used for the trapping and preconcentration of analytes with different molecular sieves targeting different analyte sizes (shown as the number of carbons in the molecule in Figure 3). The preconcentrators can employ a single sieve or multiple-sieve configurations (4-sieve configuration in Figure 3). A vacuum pump is used to pull samples across the preconcentrator where target analytes are trapped and accumulate with increased sampling time. Once sampling is completed, the vacuum pump is turned off and μ-valves switch to allow the flow of carrier gas (He) through the preconcentrator and to the μ-column. The preconcentrator is resistively heated to desorb the trapped analytes for separation on the μ-column. The μ-column is made of square spiral channels from DRIE silicon wafers of dimensions 3 x 3 cm or 3 x 6 cm for 5- and 10-m effective column length, respectively. The square spiral channels are coated with a variety of liquid stationary phases to target different analyte selectivity within each μ-column. Finally, at the exit of the μ-column, the separated analytes pass through high sensitivity μ-detectors for detection. The μ-detectors employed are a micro-photoionization detector (μ-PID) sensitive to most organics and a micro-helium dielectric barrier discharge photoionization detector (μ-HD-PID) sensitive to fixed gases (minus helium and neon). The MEMS technology significantly decreases the size, weight, and power (SWaP) of the device thereby enabling multiple μ-GCs in a single enclosure, referred to as a μ-GC suite (Figure 4) [5].

            In this presentation, we focus on ALPACA hardware development and the recent advances that have been made to impact future landed missions.

References

[1]      K.A. Duval, et al., Biosignature preparation for ocean worlds ( BioPOW ) instrument prototype, (2023) 2023–2032. https://doi.org/10.3389/fspas.2023.1244682.

[2]      T. Van Volkenburg, et al., Microfluidic Chromatography for Enhanced Amino Acid Detection at Ocean Worlds, Astrobiology. 22 (2022) 1116–1128. https://doi.org/10.1089/AST.2021.0182/SUPPL_FILE/SUPP_DATA.PDF.

[3]      R.C. Blase, et al., Experimental Coupling of a MEMS Gas Chromatograph and a Mass Spectrometer for Organic Analysis in Space Environments, ACS Earth Sp. Chem. 4 (2020) 1718–1729. https://doi.org/10.1021/acsearthspacechem.0c00131.

[4]      R.C. Blase, et al., MEMS GC Column Performance for Analyzing Organics and Biological Molecules for Future Landed Planetary Missions, Front. Astron. Sp. Sci. 9 (2022) 828103 (1–19). https://doi.org/10.3389/FSPAS.2022.828103.

[5]      R. Blase, et al., Biosignature detection from amino acid enantiomers with portable GC systems, Adv. Devices Instrum. (2024) 11–23. https://doi.org/10.34133/adi.0049.

 

Figure 1. BioPOW a) sample processing scheme, consisting of the B) sample cup, 1cm scale bar, C) wet lab manifold with cation exchange cartridge, 4 cm scale bar and D) concentration and derivatization tank, 1 cm scale bar. E) Integrated operational workflow where sample loading (gray box) is assumed performed by an external system (from [1]).

 

Figure 2. BioPOW system overview that 1) melts ice sample, 2) purifies amino acids, and 3) dries amino acids to concentrate and derivatizes for downstream GC analysis. 2b) Overview of steps in the cation exchange process, modified from [2].

 

Figure 3. Diagram of preconcentrator, from ref [5], used in μ-GC for preconcentrating analytes prior to desorption onto the μ-column for separation of complex sample mixtures.

 

Figure 4. μ-GC suite layout using multiple preconcentrators, μ-GCs, and μ-detectors for analyte selectivity in each μ-GC and broad chemical coverage over the entire suite.