In past times, life might have emerged under Martian conditions milder than the present ones, and left some remnants at the surface. Even if this did not happen, prebiotic molecules may have been preserved in the soil, and they might be similar to those that prevailed on the Earth surface some 3.5 to 4 billion years ago. NASA's MSL2011 rover Curiosity will explore the surface and subsurface of Mars, seeking traces of prebiotic or biological activity. Organic signatures are among the main signatures of interest in this frame, and they will be among the main targets of the Gas Chromatograph Quadrupole Mass Spectrometer (GC-QMS) which constitutes the core of the Sample Analysis at Mars (SAM) analytical laboratory, developed by the NASA/GSFC in collaboration with the University of Paris (Fr) and the JPL. The main goal of this instrumentation is indeed to determine molecular abundances and isotopic ratios of organic molecules present in the collected samples, by analyzing gases either sampled from the atmosphere, or obtained from soil processing, either by physical heating or chemical reactions. In order to prepare for the interpretation of the data obtained in situ with the GCQMS of SAM, and due to the complexity of this instrumentation, a number of calibrations are required to determine the exact behaviour of each part of this instrumentation, that is required to correctly treat the signal and obtain a correct interpretation of it. In order to prepare the SAM-GC in situ results treatment and interpretation, it is necessary: (1) to determine the instrument ability to detect targets molecules under the instrument operating conditions and (2) to create data bases to help for the identification and quantification of the molecules that could be detected with SAM. With this aim we first selected molecules which might be analyzed with SAM-GC using the following criteria: (1) abundance at the Mars surface (2) astrobiological interest, (3) formation during the sample preparation. Then we characterized these target molecules with laboratory instrumentation using discrete spare components of the GC flight model ; in a second step, we used a SAM-GC spare model, in a vacuum chamber roughly reproducing the environmental conditions inside the Curiosity rover. A following step will be to carry out similar experiments with the whole SAM testbed located at the NASA/GSFC. This paper will present an overview of the analytical capabilities of the GC-QMS, with a focus on the GC part, relying on the calibration described previously. In addition, we will present analyses done on Atacama soil samples, Mars soil analogue, to get an evaluation of the SAM GC performances with a natural sample.