Chemometric evaluation of time-of-flight secondary ion mass spectrometry data of minerals in the frame of future in situ analyses of cometary material by COSIMA onboard ROSETTA Cecile Engrand 1 , Jochen Kissel 2 , Franz R. Krueger 3 , Philippe Martin 4 , Johan Sile ´n 5 , Laurent Thirkell 4 , Roger Thomas 4 and Kurt Varmuza 6 * 1 Centre de Spectrome ´ trie Nucle ´aire et de Spectrome ´trie de Masse, CNRS-Univ. Paris XI, F-91405 Orsay Campus, France 2 Max Planck Institute for Solar System Research, D-37191 Katlenburg-Lindau, Germany 3 Ingenieurbureau Dr. Krueger, Messeler Strasse 24, D-64291 Darmstadt, Germany 4 Laboratoire de Physique et de Chimie de l’Environnement, 3A av. de la Recherche Scientifique, F-45071 Orle ´ans Cedex 2, France 5 Finnish Meteorological Institute, FIN-00101 Helsinki, Finland 6 Vienna University of Technology, Institute of Chemical Engineering, Laboratory for Chemometrics, A-1060 Vienna, Austria Received 21 September 2005; Revised 17 February 2006; Accepted 17 February 2006 Chemometric data evaluation methods for time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been tested for the characterization and classification of minerals. Potential applications of these methods include the expected data from cometary material to be measured by the COSIMA instrument onboard the ESA mission ROSETTA in the year 2014. Samples of the minerals serpentine, enstatite, olivine, and talc have been used as proxies for minerals existing in extraterrestrial matter. High mass resolution TOF-SIMS data allow the selection of peaks from inorganic ions relevant for minerals. Multivariate cluster analysis of peak intensity data by principal components analysis and the new method CORICO showed a good separation of the mineral classes. Classification by k nearest-neighbor classification (KNN) or binary decision trees (CART method) results in more than 90% correct class assignments in a leave-one-out cross validation. Copyright # 2006 John Wiley & Sons, Ltd. This study contributes to the development of methods for the evaluation of time-of-flight secondary ion mass spectro- metry (TOF-SIMS) data from mineralogical matter as expected from in situ measurements near a comet. Systematic investigations of minerals by TOF-SIMS are rare as usually other spectroscopic or crystallographic methods are prefer- entially used to characterize minerals. 1–3 For instance, metallic oxides have been analyzed by TOF-SIMS, 4,5 and an extensive overview of TOF-SIMS in cosmochemistry has been published, 6 but TOF-SIMS—together with chemometric methods—were not used in this case to recognize minerals. Furthermore, ratios of elemental con- centrations—measured by laser ablation TOF-MS—have been used to characterize meteoritic material. 7 Comets are considered the least differentiated bodies in our solar system. They still contain volatile material intimately mixed with highly refractory grains, as shown by previous in situ mass spectroscopic measurements near the comets Halley, 8 Hale-Bopp, 9,10 and Wild-2. 11 These results lent strong support to the models of J. Mayo Greenberg 12 on how a comet is made. While the high relative speed for the Halley fly-by missions allowed only a gross characterization of the organic material, the next mission with a dust mass spectrometer, STARDUST, allowed a more detailed analysis and the identification of a few more substance classes. 13 The in situ analytical technique applicable with fly-by missions is handicapped by the high relative speeds of more than 5 km/s of impacting dust particles; under these conditions, the mass of a particle has a large effect on the shape of the mass spectrum. 14 For a more refined analysis of the physical structure and chemical composition of cometary material, a cold-sample return mission would be the best. In January 2006, the STARDUST cometary mission 15 returned a non-cooled sample of comet Wild 2 dust that will give us some insights on cometary matter. The ROSETTA mission is on its way to rendezvous with comet P67/Churyumov-Gerasimenko in the year 2014. A time-of-flight secondary ion mass spec- trometer—named COSIMA—has been selected for in situ analyses of cometary dust onboard ROSETTA. TOF-SIMS is an established laboratory technique, which gives access to the composition of the first few atomic layers of a sample. The method provides two advantageous features: (1) during ion formation, the information on the RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2006; 20: 1361–1368 Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rcm.2448 *Correspondence to: K. Varmuza, Vienna University of Technology, Institute of Chemical Engineering, Laboratory for Chemometrics, Getreidemarkt 9/166, A-1060 Vienna, Austria. E-mail: kvarmuza@email.tuwien.ac.at Contract/grant sponsor: CNES. Copyright # 2006 John Wiley & Sons, Ltd.