Evaluation of mass spectra from organic compounds assumed to be present in cometary grains. Exploratory data analysis

Abstract

From about 60 organic compounds, mass spectra have been measured by 252 Cf ionization mass spectrometry (PDMS). The substances and the data are relevant for future experiments near a comet by the space research project COSIMA (a time-of-flight mass spectrometer for secondary ions) on board of the ESA mission ROSETTA. The spectra have been transformed into a set of appropriate spectral features (x-variables); the corresponding chemical structures have been characterized by binary substructure descriptors (y-variables). PLS-2 mappings exhibit good correlations between the x-and the y-components. PLS spectrum±substructure mappings supported the detection of structural classes that are well reflected by spectral data. PCA with spectral data was less efficient for this purpose. The found structural classes are candidates for the development of spectral classifiers for the COSIMA project. Interpretation of the loading plots indicated spectral properties which are characteristic for substance classes.

Time‐of‐flight mass spectrometric analysis of ion formation in hypervelocity impact of organic polymer microspheres: comparison with secondary ion mass spectrometry, 252Cf mass spectrometry and laser mass spectrometry

“…A similar instrument had been used by Tascon Co. (Münster, Germany)7 to record SIMS spectra of polystyrene. The 252 Cf‐TOF mass spectra (for comparison of some ion types, see below) were taken with a BIO‐ION mass spectrometer at Vienna, Austria 8. Some positive ion mass spectra of similar microspheres were recorded by Werther in Vienna, Austria, using a MALDI‐TOF instrument (without a matrix, however).…”

Cosima – High Resolution Time-of-Flight Secondary Ion Mass Spectrometer for the Analysis of Cometary Dust Particles onboard Rosetta

“…A spectral feature is a numerical variable that characterizes a spectrum; it is a linear or nonlinear function of all or selected peak intensities. Varmuza et al (1999Varmuza et al ( , 2001 and Werther et al (2002) have tested different types of spectral features using data that are similar to TOF-SIMS data. They found that promising concepts for feature generation for organic compunds are (1) intensities at selected masses, (2) intensities averaged in selected mass intervals, (3) logarithmic ratios of selected intensities, (4) summation of intensities at fixed mass differences (e.g., 14: modulo-14), and (5) autocorrelation.…”

Mass Spectrometry

“…Therefore, new variables (''spectral features'') are calculated by mathematical transformations of the original peak list data [105]. Spectral features are often normalized (e.g., to a constant sum) and calculation can be restricted to limited mass ranges.…”