Trimethylsulfoniumhydroxide (TMSH) as a Thermochemolysis Reagent for Detecting Fatty Acids in Mars and Ceres-analog Samples

Abstract:

The Sample Analysis at Mars (SAM) instrument aboard the Curiosity rover is the latest in a line of instruments using GC-MS to search for organic compounds in extraterrestrial environments. SAM contains the thermochemolysis reagent TMAH (tetramethylammonium hydroxide) in 25% methanol to greatly increase the yield of fatty acid methyl esters in Mars samples in comparison to direct pyrolysis. Here, we assess the utility of TMSH (trimethylsulfonium hydroxide) in 25% methanol as a potential methylation reagent for detecting fatty acids on future missions by using it in GC-MS experiments on a set of rock samples from Mars and Ceres-analog environments. Natural siliceous sinter and schwertmannite Mars-analog samples, and ammoniated-nontronite and ammoniated-montmorillonite Ceres-analog samples generated in the lab via cation exchange reactions were analyzed with pyrolysis-only, TMAH, and TMSH thermochemolysis techniques. Results show that TMSH may be an adequate replacement for TMAH for certain mineralogies. On siliceous sinter samples, TMSH yielded the same amount of FAMES as TMAH, and yielded more small-carbon chain FAMES on both the siliceous sinter, and the schwertmannite deposits. The ammonia-rich samples contained very low abundance alkanes revealed under pyrolysis, and fatty acid assessment is ongoing. By assessing TMSH as a thermochemolysis reagent and optimizing its utility, we can potentially improve methods of GC-MS detection of biosignatures on other worlds.