An analytical procedure, based on the study of the Autocovariance Function, is described to study isothermal GC chromatograms of multicomponent mixtures. Isothermal GC analysis is the method of choice in space missions since it is, to date, the only method compatible with flight constraints. Isothermal GC chromatograms look inhomogeneous and disordered with peak density decreasing at higher retention times: a time axis transformation is required to make retention a homogeneous process so that CH2 addition in terms of a homologous series yields constant retention increment. The order introduced into the chromatogram by retention time linearization can be simply singled out by the experimental autocorrelation function (EACF) plot: if constant interdistances are repeated in different regions of the chromatogram, well-shaped peaks are evident in the EACF plot. By comparison with a standard mixture, it is possible to identify peaks diagnostic of specific molecular structures: the study of the EACF plot provides information on sample chemical composition. The procedure was applied to standard mixtures containing compounds representative of the planetary atmospheres -- hydrocarbons, nitriles ans oxigenated compounds with between 3 and 12 carbon atoms -- analyzed in flight simulating conditions. The coupling of the selectivity of the SIM detection with the interpretation power of the EACF procedure proves to be a powerful tool for interpreting data recovered from space missions: the chemical composition of unknown mixtures can be dentified by handling the raw SIM chromatogram.
GC-MS in space research: Decoding complex isothermal chromatograms recovered from space missions
PIETROGRANDE, Maria Chiara;ZAMPOLLI, Mariagrazia;DONDI, Francesco
2004
Abstract
An analytical procedure, based on the study of the Autocovariance Function, is described to study isothermal GC chromatograms of multicomponent mixtures. Isothermal GC analysis is the method of choice in space missions since it is, to date, the only method compatible with flight constraints. Isothermal GC chromatograms look inhomogeneous and disordered with peak density decreasing at higher retention times: a time axis transformation is required to make retention a homogeneous process so that CH2 addition in terms of a homologous series yields constant retention increment. The order introduced into the chromatogram by retention time linearization can be simply singled out by the experimental autocorrelation function (EACF) plot: if constant interdistances are repeated in different regions of the chromatogram, well-shaped peaks are evident in the EACF plot. By comparison with a standard mixture, it is possible to identify peaks diagnostic of specific molecular structures: the study of the EACF plot provides information on sample chemical composition. The procedure was applied to standard mixtures containing compounds representative of the planetary atmospheres -- hydrocarbons, nitriles ans oxigenated compounds with between 3 and 12 carbon atoms -- analyzed in flight simulating conditions. The coupling of the selectivity of the SIM detection with the interpretation power of the EACF procedure proves to be a powerful tool for interpreting data recovered from space missions: the chemical composition of unknown mixtures can be dentified by handling the raw SIM chromatogram.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
