The search for signs of past or present extraterrestrial life requires autonomous instrumentation capable of robust and highly sensitive in situ analysis of a broad range of organic compound classes. The Mars Organic Analyzer (MOA) is a portable microchip capillary electrophoresis (&muCE) instrument developed for highly sensitive chemical biomarker analysis. This thesis expands the capabilities of the MOA to highly-sensitive analysis of PAHs, aldehydes, ketones, and carboxylic acids in conventional and extremely acidic and saline samples, and demonstrates proof-of-principle for using programmable valve arrays for autonomous sample processing.
A &muCE separation and analysis method for PAHs is optimized, resulting in baseline separation of a nine-PAH standard with limits of detection (LODs) ranging from 2000 ppm to 6 ppb. Analysis of an environmental contamination standard from Lake Erie and a hydrothermal vent chimney sample agree with published composition; analysis of a Martian analogue sample from the Yungay Hills (Atacama Desert) is found to contain several PAHs at ppm levels.
Pacific Blue succinimidyl ester is used as an improved fluorescent label for amines and amino acids enabling sub-pptr LODs, and a micellar electrokinetic chromatography (MEKC) method is developed for enhanced compositional analysis. These methods are applied to the analysis of samples from the Murchison meteorite and the Yungay hills (Atacama Desert).
Previous MOA analysis methods suffer from artificially low signal and resolution when samples are acidic, saline, or contain polyvalent cations. To address this challenge, new analysis, labeling, and dilution buffers are developed. Higher ionic strength buffer systems provide better buffering capacity and salt tolerance, and addition of ethylamine-diaminetetraacetic (EDTA) acid effectively neutralizes deleterious effects of multivalent cations. These optimized methods enable analysis of amino acids in a brine sample from Saline Valley, California, and a subcritical water extract of a highly acidic sample from the Rio Tinto, Spain.
MOA analysis methods for oxidized organic carbon are developed and optimized using the fluorescent probe Cascade Blue hydrazide (CB). Hydrazone formation of CB with aldehydes and ketones requires pH 5-6, CB-labeling of 1-ethyl-3[3-dimethylaminopropyl]carbodiimide (EDC) activated carboxylic acids is optimized to pH 3, and separations are optimized at pH 9.5, 20 oC. Standards developed based on oxidized organics detected in the Murchison meteorite are analyzed, with pM - nM LODs. Aldehyde and ketone analyses are validated via the analysis of several fermented beverages and a basaltic Martian simulant sample. Several polycarboxylic derivatives of benzene, including mellitic acid, are analyzed, demonstrating the first analysis of these highly oxidized molecules on a portable instrument. Successful analyses of carboxylic acids in a lava tube cave sample (Mojave Desert, CA) and a Bumpass Hell hydrothermal area sample (Lassen National Park) demonstrate the utility and versatility of this method.
Finally, an autonomous sample processing system based on the programmable microfluidic rectilinear array Automaton is demonstrated at a proof-of-concept level. Prospects for further development of this sample processing system are considered, as are further enhancements of the total analysis system. The methods developed here are also critically compared to other proposed in situ life detection instruments.