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Project Progress

(1) The two-step laser MS (L2MS) protocol, as compared to one-step, or prompt, laser desorption (LDMS), was further developed based on the substantial initial work in 2012-2013. In this period, the concept of using the tunability of the desorption laser, rather than the traditional resonance ionization approach, was examined. Figure 1 shows an example set of spectra using IR desorption and UV post-ionization, as usual, but where the IR laser wavelength is varied over the range of 2800 to 3200 nm, which not only covers the well-known water absorption feature (for analysis of ice-rich samples) but also the vibrational modes of a range of aromatic compounds. The target material (bulk Murchison powder) is known to contain PAHs (in relatively high abundance) and their methylated homologues as components of both soluble and insoluble fractions. These are revealed specifically in the relevant IR range representing an increase in selectivity of several orders of magnitude. Results from this and related L2MS investigations are being prepared for submission to a peer reviewed journal.

(2) The tandem MS (or, MS/MS) capability is the deliberate fragmentation of isolated gas-phase molecules to allow focused structural analysis. In the last report period, we demonstrated the operation of a “pseudo-tandem” mode of the time-of-flight (TOF) MS instrument (also used for L2MS) – so-called because the fragmentation is carried out externally and on a subsequent analysis of the primary spectrum, assuming consistency. In recent work, using the breadboard and later the engineering model of the Mars Organic Molecule Analyzer (MOMA) in development for the ExoMars rover, we have carried out comparative MS/MS analyses with a linear ion trap. Ion traps support MS/MS “in space” implying the trapped ion population may be scanned, isolated, and fragmented within the trapping volume.

The GCA support specifically covered the conceptualization of developing an autonomous MS/MS capability (not in the minimum requirements on ExoMars), which would use data-dependent algorithms to return structural information in every series of runs rather than having to wait for humans-in-the-loop decisions. This may be critical in Mars operations where evidence of certain compounds may be “fleeting” (e.g., if they are surficial trace coatings on mineral surfaces that attenuate with repeated laser analyses. Figure 2 shows an example spectrum of the small peptide Angiotensin II (m/z 1047) which has been isolated and processed via MS/MS. The lower-m/z fragments are ‘y’ and ‘b’ ions known from the distinctive pattern of amino acid losses, effectively sequencing the detected peptide within a single spectrum.