The SAM/MSL Terrestrial Background Spectral Library is one of the tools developed for identifying known terrestrial background for the Mars Science Laboratory (MSL) Sample Analysis at Mars (SAM) mission. The SAM instrument suite can detect trace elements in the ppb range and therefore requires a robust library and informational structure to aid it in identification of source origin. It is unique in that it is the first spectral library developed containing spectra of more than 800 gas chromatography mass spectrometry (GCMS) files generated from analysis of actual rover materials. The terrestrial background library will help ensure that the spectral identifications remain accurate, and also determine whether the spectra arise from the Mars or Earth environment.

The development of an organic terrestrial background library allows for the identification of compounds found on Earth that would be inadvertently detected in the Mars soil and gaseous samples as impurities. As such, this library will prove useful for the SAM instrumentation analysis on Curiosity Mars Rover.

The process of analyzing an unknown GCMS data file begins by performing a similarity and identity search using mass spectral analysis software [AMDIS (Automated Mass Spectral Deconvolution and Identification System), IFD (Ion Finger-print Deconvolution, ACD (Advanced Chemistry Development)]. The most likely spectrum of one kind of search is compared with the one from the other type, and the most probable compound identity determined.

IFD software is utilized to identify and select the most significant total ion chromatogram (TIC) peaks. The spectrum for each of the peaks identified in the NIST TIC peak search is obtained and exported into a standard NIST text library file. The NIST Search Library is used to read the spectrum and obtain information regarding the most likely compound to match the spectrum.

One goal of the contamination control plan is to have prior knowledge of the materials used, especially those that occupy large areas of the GSMS data space and produce multiple GCMS peaks. To achieve this, a materials testing program has been put in place. GCMS data is collected from organic-releasing materials used on the exterior of the rover and for materials used in large quantities in the interior.

This work was done by Prabhakar Misra, Raul Garcia-Sanchez, Paul Mahaffy, and Doris Jallice of Goddard Space Flight Center; and John Canham of ATK Spacecraft Systems and Services. GSC-16547-1

Software Tech Briefs Magazine

This article first appeared in the September, 2014 issue of Software Tech Briefs Magazine.

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