Statistics – Computation
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....11646p&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #11646
Statistics
Computation
Scientific paper
In the scientific payloads of current or future space probes, gas chromatography (GC) plays a predominant role to separate and identify the chemical species present in the complex environments investigated (Titan, comets, Mars). Specific requirements are imposed by flight conditions: the strongest constraint concerns energy saving imposing temperature and pressure limitations, so that isothermal GC separations are the only ones compatible with flight constrains. The low separation performance obtained under isothermal conditions results in an increase in signal involving and peak overlapping, usually present in separations of multicomponent mixtures as planetary atmospheres are. In this case, it is mandatory to use a mathematical approach to deconvolve incompletely resolved peaks and to interpret the chromatogram, in order to extract all the analytical information hidden in it, that is “ decoding ” the complex chromatogram. In this paper a chemometric approach based on the Fourier analysis is reported. It is based on the computation of Autocovariance Function (ACVF) on the experimental chromatogram. ACVF plot constitutes a fingerprint of the chromatogram since, in contrast with the original chromatogram very crowded of peaks, it retains in a simpler plot all the information on the nature and relative abundance of the compounds present in the mixture. From ACVF plot, information on the atmosphere complexity, as well as on the separation system, can be easily extracted: the number of components present in the sample can be estimated and the performance of the analytical separation can be evaluated. In order to identify the presence of an ordered retention pattern a time axis transformation is proposed, since isothermal GC chromatograms look inhomogeneous and disordered with peak density decreasing at higher retention times. The time axis is transformed into a new scale based on the retention times of n-alkanes. The order introduced into the chromatogram by retention time linearization can be simply singled out by the ACVF plot: if constant interdistances are repeated in different regions of the chromatogram, well-shaped peaks are evident in the ACVF plot. By comparison with standard mixture it is possible to identify peaks diagnostic of specific molecular structures: ACVF plot gives information on chemical composition of the sample. Applications described are specifically developed in sight of interpreting the complex chromatograms to be collected in space missions: complex samples, simulating extra-terrestrial atmosphere compositions, were analysed in the same GC analysis conditions (temperature, outlet pressure) operated by the Rosetta Lander probe.
Dondi F.
Pasti L.
Pietrogrande M. C.
Sternberg Robert
Szopa Cyril
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