Development and Characterization of Instrumentation for Future Extraterrestrial Soil Analyses: Investigation of Terrestrial Soil and Extraterrestrial Soil Analogues by Electrochemical Sensors and Ion Chromatography.
Abstract: The research presented herein discusses the analysis of Martian soil
from the Phoenix mission and the development of a new instrument to further our
understanding of remote terrestrial and extraterrestrial environments. The focus of the
Phoenix analysis work was placed on the quantification of the soluble sulfate in the
Phoenix samples and the determination of perchlorate parent salt... read mores using modelling software,
soil simulants, ion-selective electrodes and ion chromatography. The implications of these
analyses, especially the presence of CaClO4, indicate an arid
Martian environment at the Phoenix landing site. Building on the successful Phoenix
mission, as well as other un-flown instruments including the Robotic Chemical Analysis
Laboratory, a new instrument was conceived, designed, and fabricated. The new instrument,
the In-situ Chemical Analysis Laboratory and Sensor Array,
increased the sampling capabilities compared with Phoenix by decreasing the size of the
sample analysis unit while incorporating an increased number of sensors per unit. The
scalable instrument can accommodate 4-100 units upon mass fabrication. Each sample analysis
unit can house a maximum of 42 ion-selective electrodes, 3 reference electrodes, whilst
reserving one wall for other electrochemical sensors. The increased sensor redundancy will
allow for a more accurate and precise measurement of the soluble species present in the
sample. The increased number of sensors was achieved by miniaturizing and optimizing the
sensor design and materials. The final design, which utilized silver epoxy and porous
carbon with an ion-selective membrane, yielded miniaturized sensors with similar
sensitivity and stability while also increasing the overall lifetime. An investigation into
soil leaching parameters was also performed to investigate the effects of miniaturizing the
sample analysis unit from accommodating 25 mL to less than 10 mL leaching solution. Ion
chromatography showed that the greatest increase on the soluble species present in the
leachate occurred as the leach ratio (g leach solution:g soil) and leach time increased for
Antarctic soil samples. The low levels of calcium and magnesium resulted in the opposite
trend, where the concentration was decreased as the leach ratio and time increased, due to
the presence of carbonates in the leaching solution and soil sample.
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Chemistry.
Advisor: Samuel Kounaves.
Committee: Arthur Utz, Charles Sykes, and Joseph Bauer.
Keywords: Analytical chemistry, and Geochemistry.read less