An Electrochemically Based Total Organic Carbon Analyzer for Planetary and Terrestrial On-Site Applications

• Published in: Analytical chemistry (Washington) 2012-07, Vol.84 (14), p.6271-6276
• Main Authors: Stroble, Shannon T, Kounaves, Samuel P
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Carbon; Carbon dioxide; Chemistry; Chromatographic methods and physical methods associated with chromatography; Electrodes; Exact sciences and technology; Extraterrestrial life; Gas chromatographic methods; General, instrumentation; Mars; Organic chemistry; Spectrometric and optical methods
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac301704m

The search for organics on Mars began over 30 years ago. Neither the Viking GC/MS nor the more recent thermal and evolved gas analyzer (TEGA) aboard Phoenix were successful in detecting organics in the Martian soil. The most recent hypothesis for the “missing” Martian organics is thermal decomposition of organic material to CO2 during the pyrolysis step of these analyses caused by the recently discovered ∼1 wt % perchlorate in the Martian soil. To avoid this problem, an entirely different approach for the analysis of organics on Mars has been developed using an electrochemically based total organic carbon (TOC) analyzer, designated the Mars Organic Carbon Analyzer (MOCA). MOCA is designed as a small, lightweight, low-power instrument that electrochemically oxidizes organics to CO2. The CO2 is subsequently detected and quantified to determine the amount of TOC in the soil. MOCA can use the perchlorate present in the Martian soil to its advantage as an electrolyte, thus requiring only a buffered solution. Through a series of proof-of-concept tests, MOCA is shown to oxidize a variety of low-molecular-weight 1–5-carbon-containing molecules, including those containing carbon-13 using platinum and boron-doped diamond (BDD) electrodes at concentrations as low as 10 mg/kg. MOCA can also be used in terrestrial settings for on-site analysis of dissolved TOC.