939 (2001) 69–77 Journal of Chromatography A, www.elsevier.com / locate / chroma Analysis of complex mixtures recovered from space missions Statistical approach to the study of Titan atmosphere analogues (tholins) a, b b b c * M.C. Pietrogrande , P. Coll , R. Sternberg , C. Szopa , R. Navarro-Gonzalez , d a C. Vidal-Madjar , F. Dondi a Department of Chemistry, University of Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy b ´ LISA, UMR CNRS 7583, Creteil, France c LQPEP , Instituto de Ciencias Nucleares, UNAM, D.F. 04510 Mexico City, Mexico d ` Laboratoire de Recherche sur les Polymeres, CNRS, Thiais, France Received 12 July 2001; received in revised form 26 September 2001; accepted 26 September 2001 Abstract To study Titan, the largest moon of Saturn, laboratory simulation experiments have been performed to obtain analogues of Titan’s aerosols (named tholins) using different energy sources. Tholins, which have been demonstrated to represent aerosols in Titan’s haze layers, are a complex mixture, resulting from the chemical evolution of several hydrocarbons and nitriles. Their chromatographic analysis yields complex chromatograms, which require the use of mathematical procedures to extract from them all the information they contain. Two different chemometric approaches (the Fourier analysis approach and the statistical model of peak overlapping) have been successfully applied to pyrolysis–GC–MS chromatogram of a tholin sample. Fundamental information on the mixture’s chemical composition (number of components, m) and on the separation system performance (separation efficiency, s) can be easily estimated: the excellent correspondence between the data calculated by the two independent procedures proves the reliability of the statistical approaches in characterizing a tholin chromatogram. Moreover, the plot of autocorrelation function contains, in a simplified form, all the information on the retention pattern: retention recursivities can be easily singled out and related to specific molecular structure variations. Therefore, the autocorrelation function (ACF) plot constitutes a simplified fingerprint of the pyrolysis products of tholins, which can be used as a powerful tool to characterize a tholin sample.  2001 Elsevier Science B.V. All rights reserved. Keywords: Titan’s atmosphere; Aerosols; Statistical analysis; Autocorrelation function; Autocovariance function; Tholins; Volatile organic compounds 1. Introduction role in solar system explorations, in particular in space research related to exobiology, i.e., the in- Gas chromatography (GC) plays a predominant vestigation of history and abundance of biogenic elements, which throws light on the necessary con- ditions for prebiotic chemical evolution and origin of *Corresponding author. Tel.: 130-0532-291-152; fax: 130- life [1]. The study of Titan, the largest moon of 0532-240-709. E-mail address: mpc@dns.unife.it (M.C. Pietrogrande). Saturn, is very relevant to exobiology, since space 0021-9673 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0021-9673(01)01333-4